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diff --git a/.gitattributes b/.gitattributes new file mode 100644 index 0000000..d7b82bc --- /dev/null +++ b/.gitattributes @@ -0,0 +1,4 @@ +*.txt text eol=lf +*.htm text eol=lf +*.html text eol=lf +*.md text eol=lf diff --git a/LICENSE.txt b/LICENSE.txt new file mode 100644 index 0000000..6312041 --- /dev/null +++ b/LICENSE.txt @@ -0,0 +1,11 @@ +This eBook, including all associated images, markup, improvements, +metadata, and any other content or labor, has been confirmed to be +in the PUBLIC DOMAIN IN THE UNITED STATES. + +Procedures for determining public domain status are described in +the "Copyright How-To" at https://www.gutenberg.org. + +No investigation has been made concerning possible copyrights in +jurisdictions other than the United States. Anyone seeking to utilize +this eBook outside of the United States should confirm copyright +status under the laws that apply to them. diff --git a/README.md b/README.md new file mode 100644 index 0000000..a97424c --- /dev/null +++ b/README.md @@ -0,0 +1,2 @@ +Project Gutenberg (https://www.gutenberg.org) public repository for +eBook #60225 (https://www.gutenberg.org/ebooks/60225) diff --git a/old/60225-0.txt b/old/60225-0.txt deleted file mode 100644 index c7c8616..0000000 --- a/old/60225-0.txt +++ /dev/null @@ -1,6091 +0,0 @@ -The Project Gutenberg EBook of The Preparation & Mounting of Microscopic -Objects, by Thomas Davies - -This eBook is for the use of anyone anywhere in the United States and most -other parts of the world at no cost and with almost no restrictions -whatsoever. You may copy it, give it away or re-use it under the terms of -the Project Gutenberg License included with this eBook or online at -www.gutenberg.org. If you are not located in the United States, you'll have -to check the laws of the country where you are located before using this ebook. - -Title: The Preparation & Mounting of Microscopic Objects - -Author: Thomas Davies - -Release Date: September 2, 2019 [EBook #60225] - -Language: English - -Character set encoding: UTF-8 - -*** START OF THIS PROJECT GUTENBERG EBOOK PREPARATION OF MICROSCOPIC OBJECTS *** - - - - -Produced by deaurider, Charlie Howard, and the Online -Distributed Proofreading Team at http://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive) - - - - - - - - - - THE - PREPARATION & MOUNTING - OF - MICROSCOPIC OBJECTS. - - - BY - THOMAS DAVIES. - - - LONDON: - ROBERT HARDWICKE, 192, PICCADILLY. - AND ALL BOOKSELLERS. - - - - -_A New Edition, Revised and Enlarged._ - -_Price 2s. 6d. plain; 4s. coloured._ - -HALF-HOURS WITH THE MICROSCOPE. A Popular Guide to the Use of the -Microscope as a Means of Amusement and Instruction. With Drawings of -250 objects from Nature, by TUFFEN WEST. By E. LANKESTER, M.D., F.R.S. - - -CONTENTS: - - Half an hour on the Structure. - Half an hour in the Garden. - Half an hour in the Country. - Half an hour at the Pondside. - Half an hour at the Seaside. - Half an hour Indoors. - Appendix: the Preparation and Mounting of Objects. - - -_Fcp. 8vo., 6s. beautifully illustrated by hand-painting._ - -RUST, SMUT, MILDEW, AND MOULD under the MICROSCOPE: a Plain and Easy -Guide to the Study of Microscopic Fungi. By M. C. COOKE. Coloured -Plates of over 300 Figures. - - -London: ROBERT HARDWICKE, 192, Piccadilly; and all Booksellers. - - - - -PREFACE. - - -In bringing this Handbook before the public, the Author believes that -he is supplying a want which has been long felt. Much information -concerning the “Preparation and Mounting of Microscopic Objects” has -been already published; but mostly as supplementary chapters only, -in books written professedly upon the Microscope. From this it is -evident that it was necessary to consult a number of works in order -to obtain anything like a complete knowledge of the subject. These -pages, however, will be found to comprise all the most approved methods -of mounting, together with the results of the Author’s experience, -and that of many of his friends, in every department of microscopic -manipulation; and as it is intended to assist the beginner as well -as the advanced student, the very rudiments of the art have not been -omitted. - -As there is a diversity of opinion as to the best mode of proceeding in -certain cases, numerous quotations have been made. Wherever this has -been done, the Author believes that he has acknowledged the source from -which he has taken the information; and he here tenders his sincere -thanks to those friends who so freely allowed him to make use of their -works. Should, however, anyone find his own process in these pages -_unacknowledged_, the author can only plead oversight, and his regret -that such should have been the case. - - - - -CONTENTS - - PAGE - PREFACE iii - - - CHAPTER I. - - APPARATUS. 1 - - - CHAPTER II. - - TO PREPARE AND MOUNT OBJECTS “DRY.” 22 - - - CHAPTER III. - - MOUNTING IN CANADA BALSAM. 56 - - - CHAPTER IV. - - PRESERVATIVE LIQUIDS, ETC., PARTICULARLY WHERE CELLS ARE USED. 83 - - - CHAPTER V. - - SECTIONS AND HOW TO CUT THEM, WITH SOME REMARKS ON DISSECTION. 96 - - - CHAPTER VI. - - INJECTION. 122 - - - CHAPTER VII. - - MISCELLANEOUS. 140 - - - INDEX. 153 - - - - -THE - -PREPARATION AND MOUNTING - -OF - -MICROSCOPIC OBJECTS. - - - - -CHAPTER I. - -APPARATUS. - - -Before entering into the subject of the setting of Objects for -the Microscope, the student must be convinced of the necessity of -cleanliness in everything relating to the use of that instrument. In -no branch is this more apparent than in the _preparation_ of objects; -because a slide which would be considered perfectly clean when viewed -in the ordinary way is seen to be far otherwise when magnified some -hundreds of diameters; and those constant enemies, the floating -particles of dust, are everywhere present, and it is only by unpleasant -experience that we fully learn what _cleanliness is_. - -Any object which is to be viewed under the microscope must, of course, -be supported in some way--this is now usually done by placing it upon a -glass slide, which on account of the transparency has a great advantage -over other substances. These “slides” are almost always made of one -size, viz., three inches long by one broad, generally having the edges -ground so as to remove all danger of scratching or cutting any object -with which they may come in contact. The glass must be very good, -else the surface will always present the appearance of uncleanliness -and dust. This dusty look is very common amongst the cheaper kinds of -slides, because they are usually “sheet” glass; but is seldom found -in those of the quality known amongst dealers by the name of “patent -plate.” This latter is more expensive at first, but in the end there -is little difference in the cost, as so many of the cheaper slides -cannot be used for delicate work if the mounted object is to be seen in -perfection. These slides vary considerably in thickness; care should, -therefore, be taken to sort them, so that the more delicate objects -with which the higher powers are to be used maybe mounted upon the -_thinnest_, as the light employed in the illumination is then less -interfered with. To aid the microscopist in this work, a metal circle -may be procured, having a number of different sized openings on the -outer edge, by which the glass slides can be measured. These openings -are numbered, and the slides may be separated according to these -numbers; so that when mounting any object there will be no need of a -long search for that glass which is best suited to it. - -When fresh from the dealer’s hands, these slides are generally -covered with dust, &c., which may be removed by well washing in clean -rain-water; but if the impurity is obstinate, a little washing soda -may be added, care being taken, however, that every trace of this is -removed by subsequent waters, otherwise the crystals will afterwards -form upon the surface. A clean linen cloth should be used to dry the -slides, after which they may be laid by for use. Immediately, however, -before being used for the reception of objects by any of the following -processes, all dust must be removed by rubbing the surface with clean -wash-leather or a piece of cambric, and, _if needful_, breathing upon -it, and then using the leather or cambric until perfectly dry. Any -small particles left upon the surface may generally be removed by -blowing gently upon it, taking care to allow no damp to remain. - -We have before said, that any object to be viewed in the microscope -must have its support; but if this object is to be preserved, care -must be taken that it is defended from the dust and other impurities. -For this purpose it is necessary to use some transparent cover, the -most usual at one time being a plate of mica, on account of its -thinness; this substance is now, however, never used, thin glass being -substituted, which answers admirably. Sometimes it is required to -“_take up_” as little space as possible, owing to the shortness of -focus of the object-glasses. It can be procured of any thickness, from -one-fiftieth to one-two-hundred-and-fiftieth of an inch. On account -of its want of strength it is difficult to cut, as it is very liable -to “_fly_” from the point of the diamond. To overcome this tendency -as much as possible, it must be laid upon a thicker piece, previously -made wet with water, which causes the thin glass to adhere more firmly, -and consequently to bear the pressure required in cutting the covers. -The process of cutting being so difficult, especially with the thinner -kinds, little or nothing is gained by cutting those which can be got -from the dealers, as the loss and breakage is necessarily greater in -the hands of an amateur. It is convenient, however, to have on hand a -few larger pieces, from which unusual sizes may be cut when required. - -If the pieces required are _rectangular_, no other apparatus will be -required save a diamond and a flat rule; but if _circles_ are wanted, -a machine for that purpose should be used (of which no description -is necessary here). There are, however, other contrivances which -answer tolerably well. One method is, to cut out from a thick piece of -cardboard a circle rather larger than the size wanted. Dr. Carpenter -recommends metal rings with a piece of wire soldered on either side; -and this, perhaps, is the best, as cardboard is apt to become rough at -the edge when much used. A friend of mine uses thin brass plates with -circles of various sizes “turned” through them, and a small raised -handle placed at one end. The diamond must be passed round the inner -edge, and so managed as to meet again in the same line, in order that -the circle may be true, after which they may be readily disengaged. The -sizes usually kept in stock by the dealers are one-half, five-eighths, -and three-quarters inch diameter; but other sizes may be had to order. - -For the information of the beginner it may be mentioned here that the -price of the circles is a little more than of the squares; but this -is modified in some degree by the circle being rather lighter. If -appearance, however, is cared for at all, the circles look much neater -upon the slides when not covered with the ornamental papers; but if -these last are used (as will shortly be described) the squares are -equally serviceable. - -As before mentioned, the thin glass is made of various thicknesses, -and the beginner will wish to know which to use. For objects requiring -no higher power than the one-inch object-glass, the thicker kinds -serve well enough; for the half-inch the medium thickness will be -required; while, for higher powers, the thinnest covers must be used. -The “test-objects” for the highest powers require to be brought so -near to the object-glass that they admit of the very thinnest covering -only, and are usually mounted betwixt glasses which a beginner would -not be able to use without frequent breakage; but if these objects were -mounted with the common covers, they would be really worthless with the -powers which they require to show them satisfactorily. - -It may be desirable to know how such small differences as those betwixt -the various thin glass covers can be measured. For this purpose there -are two or three sorts of apparatus, all, however, depending upon the -same principle. The description of one, therefore, will be sufficient. -Upon a small stand is a short metal _lever_ (as it may be termed) which -returns by a spring to one certain position, where it is in contact -with a fixed piece of metal. At the other end this lever is connected -with a “finger,” which moves round a dial like that of a watch, -whereupon are figures at fixed distances. When the lever is separated -from the metal which is stationary, the other end being connected -with the “finger” of the dial, that “finger” is moved in proportion -to the distance of the separation. The thin glass is, therefore, -thrust betwixt the end of the lever and fixed metal, and each piece is -measured by the figures on the dial in stated and accurate degrees. -This kind of apparatus, however, is expensive, and when not at our -command, the thin glass may be placed edgewise in the stage forceps, -and measured very accurately with the micrometer. - -Cleanliness with the thin glass is, perhaps, more necessary than with -the slides, especially when covering objects which are to be used with -a high power; but it is far more difficult to attain, on account of -the liability to breakage. The usual method of cleaning these covers -is as follows:--Two discs of wood, about two inches in diameter, are -procured, one side of each being perfectly flat and covered with clean -wash-leather. To the other side of these a small knob is firmly affixed -as a handle, or where practicable the whole may be made out of a solid -piece. In cleaning thin glass, it should be placed betwixt the covered -sides of the discs, and may then be safely rubbed with a sufficient -pressure, and so cleaned on both sides by the leather. If, however, -the glass be greasy, as is sometimes the case, it must be first washed -with a strong solution of potash, infusion of nut-galls, or any of -the commonly used grease-removing liquids; and with _some_ impurities -water, with the addition of a few drops of strong acid, will be found -very useful, but this last is not often required. - -The above method of cleaning thin glass should always be used by -beginners; but after some experience the hand becomes so sensitive -that the above apparatus is often dispensed with, and the glasses, -however thin, may be safely cleaned betwixt the fingers and thumb with -a cambric handkerchief, having first slightly damped the ends of the -fingers employed to obtain firm hold. When the dirt is very obstinate, -breathing upon the glass greatly facilitates its removal, and the sense -of touch becomes so delicate that the breakage is inconsiderable; but -this method cannot be recommended to novices, as nothing but time spent -in delicate manipulation can give the sensitiveness required. - -It was before mentioned that the ordinary glass slides were sometimes -worthless, _especially for fine objects_, from having a rough surface, -which presented a dusty appearance under the microscope. This -imperfection exists in some _thin glass_ also, and it is irremediable; -so that it is useless to attempt to cleanse it; nevertheless, care -should be taken not to mistake dirty glass for this roughness, lest -good glass be laid aside for a fault which does not really belong to it. - -When any object which it is desired to mount is of considerable -thickness, or will not bear pressure, it is evident that a wall must -be raised around it to support the thin glass--this is usually termed -a “cell.” There are various descriptions of these, according to the -class of objects they are required to protect; and here may be given a -description of those which are most generally used in mounting “dry” -objects, leaving those required for the preservation of liquids until -we come to the consideration of that mode of mounting. Many have made -use of the following slides. Two pieces of hard wood of the usual size -(3 in. by 1 in.), not exceeding one-sixteenth of an inch in thickness, -are taken, and a hole is then drilled in the middle of one of these -of the size required. The two pieces are then united by glue or other -cement, and left under pressure until thoroughly dry, when the cell is -fit for use. Others substitute cardboard for the lower piece of wood, -which is less tedious, and is strong enough for every purpose. This -class of “cell” is, of course, fitted for opaque objects only where -no light is required from below; and as almost all such are better -seen when on a dark background, it is usual to fix a small piece of -black paper at the bottom of the cell upon which to place them. For -very small objects the “grain” which all such paper has when magnified -detracts a little from the merit of this background; and lately I -have used a small piece of thin glass covered on the back with black -varnish, and placed the object upon the smooth untouched side. - -Another method of making these cells is as follows:--Two “punches,” -similar to those used for cutting “gun-wads,” are procured, of such -sizes that with the smaller may be cut out the centre of the larger, -leaving a ring whose side is not less than one-eighth of an inch wide. -These rings may be readily made, the only difficulty being to keep the -sides parallel; but a little care will make this easy enough. For this -purpose close-grained cardboard may be conveniently used. It must have -a well-glazed surface, else the varnish or cement used in affixing the -thin glass cover sinks into the substance, and the adherence is very -imperfect. When this takes place it is easily remedied by brushing over -the surface of the cardboard a strong solution of gum or isinglass; and -this application, perhaps, closes also the pores of the card, and so -serves a double purpose. But, of course, the gum must be _perfectly_ -dried before the ring is used. - -For cardboard, gutta-percha has been substituted, but cannot be -recommended, as it always becomes brittle after a certain time, never -adheres to the glass with the required firmness, and its shape is -altered when worked with even a little heat. Leather is often used, and -is very convenient; it should be chosen, however, of a close texture, -and free from oil, grease, and all those substances which are laid upon -it by the “dressers.” - -Rings of cardboard, &c., have been rejected by persons of great -experience, because they are of such a nature that dampness can -penetrate them. This fault can be almost, if not totally, removed by -immersing them in some strong varnish, such as the asphalt varnish -hereinafter mentioned; but they must be left long enough when affixed -to the glass slide to become _perfectly dry_, and this will require a -much longer time than at first would be supposed. - -There has, however, been lately brought out what is termed the _ivory -cell_. This is a ring of ivory-like substance, which may be easily and -firmly fixed to the glass slide by any of the commonly-used cements, -and so forms a beautiful cell for any dry objects. They are made of -different sizes, and are not expensive. - -Sometimes slides are used which are made by taking a thin slip of wood -of the usual size (3 in. by 1 in.), in the centre of which is cut a -circular hole large enough to receive the object. A piece of thin -glass is fixed underneath the slide, forming a cell for the object, -which may then be covered and finished like an ordinary slide. This -has the advantage of serving for transparent objects for which the -before-mentioned wooden slides are unsuitable. A slight modification -of this plan is often used where the thickness of the objects is -inconsiderable, especially with some of the Diatomaceæ, often termed -“test-objects.” The wooden slide is cut with the central opening as -above, and two pieces of thin glass are laid upon it, betwixt which the -diatoms or other objects are placed, and kept in their proper position -by a paper cover. This arrangement is a good one, insomuch as the very -small portion of glass through which the light passes on its way to the -microscope from the reflector causes the refraction or interference to -be reduced to the lowest point. - -A novice would naturally think the appearance of some of the slides -above mentioned very slovenly and unfinished; but they are often -covered with ornamental papers, which may be procured at almost every -optician’s, at a cost little more than nominal, and of innumerable -patterns and colours. How to use these will be described in another -place. - -It is very probable that a beginner would ask his friend what kind of -slides he would advise him to use. Almost all those made of wood are -liable to warp more or less, even when the two pieces are separate or -of different kinds; those of cardboard and wood are generally free -from this fault, yet the slides, being opaque, prevent the employment -of the Lieberkuhn. To some extent glass slides, when covered with -ornamental papers, are liable to the same objection, as the light is -partly hindered. And sometimes the dampness from the paste, or other -substance used to affix the papers, penetrates to the object, and so -spoils it, though this may be rendered less frequent by first attaching -the _thin_ glass to the slide by some harder cement. Much time, -however, is taken up by the labour of covering the slides, which is a -matter of consideration with some. Certainly, the cost of the glass -slides was formerly great; but now they are reasonable enough in this -respect, so that this objection is removed. It is, therefore, well to -use glass slides, except where the thin glasses are employed for tests, -&c., as above. When the thin glass circles are placed upon the slides, -and the edge is varnished with black or coloured rings, the appearance -of finish is perfect. The trouble is much less than with most of -the other methods, and the illumination of the object very slightly -interfered with. - -To varnish the edges of these covers, make circles of any liquid upon -the glass slide, and perform any other “circular” work mentioned -hereafter, the little instrument known as “Shadbolt’s turntable” is -almost indispensable. It is made as follows:--At one end of a small -piece of hard wood is fixed an iron pivot about one-eighth inch thick, -projecting half an inch from the wood, which serves as a centre upon -which a round brass table three inches in diameter revolves. On the -surface of this are two springs, about one and a half inches apart, -under which the slide is forced and so kept in position, whilst the -central part is left open to be worked upon. The centre is marked, and -two circles half an inch and one inch in diameter are usually deeply -engraved upon the table to serve as guides in placing the slide, that -the ring may be drawn in the right position. When the slide is placed -upon the “table” underneath the springs, a camel-hair pencil is filled -with the varnish, or other medium used, and applied to the surface -of the glass; the table is then made to revolve, and a circle is -consequently produced, the diameter of which it is easy to regulate. - -Many objects for the microscope may be seriously injured by allowing -the fingers to touch them--many more are so minute that they cannot -be removed in this way at all, and often it is necessary to take -from a mass of small grains, as in sand, some particular particle. -To accomplish this, there are two or three contrivances recommended: -one by means of split bristles, many of which will readily be found -in any shaving brush when it has been well used. The bristles when -pressed upon any hard surface open, and when the pressure is removed -close again with a spring; but the use of these is limited. Camel-hair -pencils are of great service for this and many other purposes to the -microscopist. In _very_ fine work they are sometimes required so small -that all the hairs with the exception of one or two finer pointed ones -are removed. A few of various sizes should always be kept on hand. - -Equally necessary are fine pointed needles. They are very readily put -up for use by thrusting the “eye” end into a common penholder, so as to -be firm. The points may be readily renewed, when injured, on a common -whetstone; but when out of use they may be protected by being thrust -into a piece of cork. - -Knives of various kinds are required in some branches of microscopic -work, but these will be described where “dissection,” &c., is treated -at some length, as also various forms of scissors. In the most simple -objects, however, scissors of the usual kind are necessary. Two or -three sizes should always be kept at hand, sharp and in good order. - -A set of glass tubes, kept in a case of some sort to prevent breakage, -should form part of our “fittings” and be always cleaned immediately -after use. These are generally from six to ten inches long and from -one-eighth to a quarter of an inch in diameter. One of these should -be straight and equal in width at both ends; one should be drawn out -gradually to a fine point; another should be pointed as the last, but -be slightly curved at the compressed end, in order to reach points -otherwise unattainable. It is well to have these tubes of various -widths at the points, as in some waters the finer would be inevitably -stopped. For other purposes the fine ones are very useful, especially -in the transfer of “preservative liquids” which will come under notice -in another chapter. - -Forceps are required in almost all microscopic manipulations, and -consequently are scarcely ever omitted from the microscopic box, -even the most meagrely furnished; but of these there are various -modifications, which for certain purposes are more convenient than the -usual form. The ordinary metal ones are employed for taking up small -objects, thin glass, &c.; but when slides are to be held over a lamp, -or in any position where the fingers cannot conveniently be used, a -different instrument must be found. Of these there are many kinds; but -Mr. Page’s wooden forceps serve the purpose very well. Two pieces of -elastic wood are strongly bound together at one end, so that they may -be easily opened at the other, closing again by their own elasticity. -Through the first of these pieces is loosely passed a brass stud, -resembling a small screw, and fastened in the second, and through the -second a similar stud is taken and fixed in the first--so that on -pressure of the studs the two strips of wood are opened to admit a -slide or other object required to be held in position. The wood strips -are generally used three or four inches long, one inch wide, and about -one-eighth inch thick. - -Again, some objects when placed upon the glass slide are of such an -elastic nature that no cement will secure the thin glass covering until -it becomes hard. This difficulty may be overcome by various methods. -The following are as good and simple as any. Take two pieces of wood -about two inches long, three-quarters wide, and one-quarter thick; -and a small rounded piece one inch long and one-quarter in diameter; -place this latter betwixt the two larger pieces. Over one end of the -two combined pass an india-rubber band. This will give a continual -pressure, and may be opened by bringing the two pieces together at -the other end; the pressure may be readily made uniform by paring the -points at the inner sides, and may be regulated by the strength of the -india-rubber band. These bands may be made cheaply, and of any power, -by procuring a piece of india-rubber tubing of the width required, and -cutting off certain breadths. Another very simple method of getting -this pressure is mentioned in the “Micrographic Dictionary.” Two pieces -of whalebone of the length required are tied together firmly at each -end. It is evident that any object placed betwixt them will be subject -to continual pressure. The power of this may be regulated by the -thickness and length of the whalebone. This simple contrivance is very -useful. - -Common watch-glasses should always be kept at hand. They are certainly -the cheapest, and their transparency makes them very convenient -reservoirs in which objects may be steeped in any liquid; as it -saves much trouble to examine cursorily under the microscope, when -the air-bubbles are expelled from insects, &c., &c. They are readily -cleaned, and serve very well as covers, when turned upside down, -to protect any objects from the dust. For this latter purpose Dr. -Carpenter recommends the use of a number of bell-glasses, especially -when one object must be left for a time (which often happens) in order -that another may be proceeded with. Wine glasses, when the “legs” are -broken, may thus be rendered very useful. - -As heat is necessary in mounting many objects, a lamp will be required. -Where gas is used, the small lamp known as “Bunsen’s” is the most -convenient and inexpensive. It gives great heat, is free from smoke, -and is readily affixed to the common gas-burner by a few feet of -india-rubber tubing. The _light_ from these lamps is small, but this is -little or no drawback to their use. Where gas is not available, the -common spirit-lamps may be used, which are very clean and answer every -purpose. - -In applying the required heat to the slides, covers, &c., it is -necessary in many cases to ensure uniformity, otherwise there is danger -of the glass being broken. For this purpose a brass plate at least -three inches wide, somewhat longer, and one-eighth of an inch thick, -must be procured. It should then be affixed to a stand, so that it may -be readily moved higher or lower, in order that the distance from the -lamp may be changed at will, and thus the degree of heat more easily -regulated. This has also the advantage of enabling the operator to -allow his slides, &c., to cool more gradually, which, in some cases, is -absolutely necessary,--as in fusing some of the salts, &c. - -In order to get rid of air-bubbles, which are frequently disagreeable -enemies to the mounter of objects, an air-pump is often very useful. -This is made by covering a circular plate of metal with a bell-glass, -both of which are ground so finely at the edges that greasing the place -of contact renders it air-tight. The pump is then joined to the metal -plate underneath, and worked with a small handle like a common syringe. -By turning a small milled head the air may be allowed to re-enter when -it is required to remove the bell-glass and examine or perform any -operation upon the object. The mode of using this instrument will be -described hereafter, but it may be here stated that substitutes have -been devised for this useful apparatus; but as it is now to be obtained -at a low cost, it is hardly worth while to consider them. Much time is, -in many instances, certainly saved by its use, as a very long immersion -in the liquids would be required to expel the bubbles, where the -air-pump would remove them in an hour. - -The next thing to be considered is what may be termed CEMENTS, some -of which are necessary in every method of mounting objects for the -microscope. Of these will be given the composition where it is -probable the young student can make use of it; but many of them are -so universally kept as to be obtainable almost anywhere; and when -small quantities only are required, economy suffers more from home -manufacture than from paying the maker’s profit. - -Amongst these, CANADA BALSAM may, perhaps, be termed the most -necessary, as it is generally used for the preservation of many -transparent objects. It is a thick liquid resin of a light amber -colour, which on exposure to the atmosphere becomes dry and hard -even to brittleness. For this reason it is seldom used as a _cement_ -alone where the surface of contact is small, as it would be apt to be -displaced by any sudden shock, especially when old. In the ordinary -method of using, however, it serves the double purpose of preserving -the object and fixing the thin glass cover; whilst the comparatively -large space upon which it lies lessens the risk of displacement. By -keeping, this substance becomes thicker; but a very little warmth will -render it liquid enough to use even when to some extent this change has -taken place. When heated, however, for some time and allowed to cool, -it becomes hardened to any degree, which may be readily regulated by -the length of time it has been exposed, and the amount of heat to which -it has been subjected. On account of this property it is often used -with chloroform: the balsam is exposed to heat until, on cooling, it -assumes a glassy appearance; it is then dissolved in pure chloroform -until it becomes of the consistence of thick varnish. This liquid is -very convenient in some cases; as air-bubbles are much more easily -got rid of than when undiluted Canada balsam is used. It also dries -readily, as the chloroform evaporates very quickly, for which reason it -must be preserved in a closely-stoppered bottle. It has been said that -this mixture becomes _cloudy_ with long keeping, but I have not found -it so in any cases where I have used it. Should it, however, become so, -a little heat will readily dispel the opacity. The ordinary balsam, -if exposed much to the air whilst being used, becomes thicker, as has -been already stated. It may be reduced to the required consistency -with common turpentine, but I have often found this in some degree -injurious to the transparency of the balsam, and the amalgamation of -the two is by no means perfect. (See also Chapter III.) The cheapness -of the article renders it no extravagance to use it always undiluted; -and when preserved in a bottle with a hollow cover fitting tightly -around the neck, both surfaces being finely ground, it remains fit for -use much longer than in the ordinary jar. - -ASPHALTUM.--This substance is dissolved in linseed oil, turpentine, or -naphtha, and is often termed “Brunswick black.” It is easily worked, -but is not generally deemed a _trustworthy_ cement, as after a time it -is readily loosened from its ground. It is, however, very useful for -some purposes (such as “finishing” the slides), as it dries quickly. I -shall, however, mention a modification of this cement a little further -on. - -MARINE GLUE.--No cement is more useful or trustworthy for certain -purposes than this. It is made in various proportions; but one really -good mixture is--equal parts of india-rubber and gum shellac; these are -dissolved in mineral naphtha with heat. It is, however, much better to -get it from the opticians or others who keep it. It requires heat in -the application, as will be explained in Chapter IV.; but it is soluble -in few, if any, liquids used by the microscopist, and for that reason -is serviceable in the manufacture of cells, &c. Where two pieces of -glass are to be firmly cemented together, it is almost always employed; -and in all glass troughs, plates with ledges, &c., the beginner may -find examples of its use. - -GOLD SIZE.--This substance may always be procured at any colourman’s -shop. The process of its preparation is long and tedious. It is, -therefore, not necessary to describe it here. Dr. Carpenter says that -it is very durable, and may be used with almost any preservative -liquids, as it is acted upon by very few of them, turpentine being its -only true solvent. If too thin, it may be exposed for awhile to the -open air, which by evaporation gradually thickens it. Care must be -taken, however, not to render it too thick, as it will then be useless. -A small quantity should be kept on hand, as it is much more adhesive -when _old_. - -LIQUID GLUE is another of these cements, which is made by dissolving -gum shellac in naphtha in such quantity that it may be of the required -consistency. This cement appears to me almost worthless in ordinary -work, as its adherence can never be relied upon; but it is so often -used and recommended that an enumeration of cements might be deemed -incomplete without it. Even when employed simply for varnishing the -outside of the glass covers, for appearance’ sake alone, it invariably -chips. Where, however, oil is used as a preservative liquid, it serves -very well to attach the thin glass; but when this is accomplished, -another varnish less liable to “chip” must always be laid upon it. (See -Chapter IV.) - -BLACK JAPAN.--This is prepared from oil of turpentine, linseed oil, -amber, gum anime, and asphalt. It is troublesome to make, and therefore -it is much better to procure it at the shops. It is a really good -cement, and serves very well to make shallow cells for liquids, as will -be described in Chapter IV. The finished cell should be exposed for a -short time to the heat of what is usually termed a “cool oven.” This -renders it very durable, and many very careful manipulators make use of -it for their preparations. - -ELECTRICAL CEMENT.--This will be found very good for some purposes -hereinafter described. To make it, melt together-- - - 5 parts of resin. - 1 ” beeswax. - 1 ” red ochre.[A] - - [A] Dr. Griffiths says that the addition of 2 parts of Canada - balsam renders this cement much more adhesive to the glass. - -It must be used whilst hot, and as long as it retains even slight -warmth can be readily moulded into any form. It is often employed in -making shallow cells for liquids, as before mentioned. - -GUM-WATER is an article which nobody should ever be without; but -labels, or indeed any substance, affixed to glass with common gum, are -so liable to leave it spontaneously, especially when kept very dry, -that I have lately added five or six drops of glycerine to an ounce of -the gum solution. This addition has rendered it very trustworthy even -on glass, and now I never use it without. This solution cannot be kept -long without undergoing fermentation, to prevent which the addition -of a small quantity of any essential oil (as oil of cloves, &c.), -or one-fourth of its volume of alcohol, may be made, which will not -interfere in any way with its use. - -There is what is sometimes termed an _extra adhesive_ gum-water, which -is made with the addition of isinglass, thus:--Dissolve two drachms of -isinglass in four ounces of distilled vinegar; add as much gum arabic -as will give it the required consistency. This will keep very well, but -is apt to become thinner, when a little more gum may be added. - -All these, except one or two, are liquid, and must be kept in -_stoppered_ bottles, or, at least, as free from the action of the air -as possible. - -When any two substances are to be united firmly, I have termed the -medium employed “a cement;” but often the appearance of the slides is -thought to be improved by drawing a coloured ring upon them, extending -partly on the cover and partly on the slide, hiding the junction of the -two. The medium used in these cases I term A VARNISH, and hereinafter -mention one or two. Of course, the tenacity is not required to be so -perfect as in the _cements_. - -SEALING-WAX VARNISH is prepared by coarsely powdering sealing wax, -and adding spirits of wine; it is then digested at a gentle heat to -the required thickness. This is very frequently used to “finish” the -slides, as before mentioned, and can easily be made of any colour by -employing different kinds of sealing-wax; but is very liable to “chip” -and leave the glass. - -BLACK VARNISH is readily prepared by adding a small quantity of -lamp-black to gold-size and mixing intimately. Dr. Carpenter recommends -this as a good finishing varnish, drying quickly and being free from -that brittleness which renders some of the others almost worthless; but -it should not be used in the first process when mounting objects in -fluid. - -Amongst these different cements and varnishes I worked a long time -without coming to any decision as to their comparative qualities, -though making innumerable experiments. The harder kinds were -continually cracking, and the softer possessed but little adhesive -power. To find hardness and adhesiveness united was my object, and the -following possesses these qualities in a great degree:-- - - India-rubber ½ drachm. - Asphaltum 4 oz. - Mineral naphtha 10 ” - -Dissolve the india-rubber in the naphtha, then add the asphaltum--if -necessary heat must be employed. - -This is often used by photographers as a black varnish for glass, and -never cracks, whilst it is very adhesive. Dr. Carpenter, however, -states that his experience has not been favourable to it; but I have -used it in great quantities and have never found it to leave the glass -in a single instance when used in the above proportions. The objections -to it are, however, I think easily explained, when it is known that -there are many kinds of pitch, &c., from coal, sold by the name of -asphaltum, some of which are worthless in making a microscopic cement. -When used for this purpose, the asphaltum must be genuine and of the -best quality that can be bought. The above mixture serves a double -purpose--to unite the cell to the slide, and also as a “finishing” -varnish. But it is perhaps more convenient to have two bottles of this -cement, one of which is thicker than common varnish, to use for uniting -the cell, &c.; the other liquid enough to flow readily, which may be -employed as a surface varnish in finishing the slides. - -The brushes or camel-hair pencils should always be cleaned after use; -but with the asphalt varnish above mentioned it is sufficient to wipe -off as carefully as possible the superfluous quantity which adheres to -the pencil, as, when again made use of, the varnish will readily soften -it; but, of course, it will be necessary to keep separate brushes for -certain purposes. - -Here it may be observed that every object should be labelled with name -and any other descriptive item as soon as mounted. There are many -little differences in the methods of doing this. Some write with a -diamond upon the slide itself; but this has the disadvantage of being -not so easily seen. For this reason a small piece of paper is usually -affixed to one end of the slide, on which is written what is required. -These labels may be bought of different colours and designs; but the -most simple are quite as good, and very readily procured. Take a sheet -of thin writing paper and brush over one side a strong solution of gum, -with the addition of a few drops of glycerine as above recommended; -allow this to dry, and then with a common gun-punch stamp out the -circles, which may be affixed to the slides by simply damping the -gummed surface, taking care to write the required name, &c., upon it -before damping it, or else allowing it to become perfectly dry first. - -There is one difficulty which a beginner often experiences in -sorting and mounting certain specimens under the microscope, viz., -the _inversion_ of the objects; and it is often stated to be almost -impossible to work without an erector. But this difficulty soon -vanishes, the young student becoming used to working what at first -seems in contradiction to his sight. - -Let it be understood, that in giving the description of those articles -which are usually esteemed _necessary_ in the various parts of -microscopic manipulation, I do not mean to say that without many of -these no work of any value can be done. There are, as all will allow, -certain forms of apparatus which aid the operator considerably; but -the cost may be too great for him. A little thought, however, will -frequently overcome this difficulty, by enabling him to make, or -get made, for himself, at a comparatively light expense, something -which will accomplish all he desires. As an example of this, a friend -of mine made what he terms his “universal stand,” to carry various -condensers, &c., &c., in the following way:--Take a steel or brass -wire, three-sixteenths or one-quarter inch thick and six or eight -inches long; “tap” into a _solid_, or make rough and fasten with melted -lead into a _hollow_, ball. (The foot of a cabinet or work-box answers -the purpose very well.) In the centre of a round piece of tough board, -three inches in diameter, make a hemispherical cavity to fit half of -the ball, and bore a hole through from the middle of this cavity, to -allow the wire to pass. Take another piece of board, about four inches -in diameter, either round or square, and one-and-a-half or two inches -thick, make a similar cavity in its centre to receive the other half -of the ball, but only so deep as to allow the ball to fit tightly when -the two pieces of board are screwed together, which last operation -must be done with three or four screws. Let the hole for the wire in -the upper part be made conical (base upwards), and so large as only to -prevent the ball from escaping from its socket, in order that the shaft -may move about as freely as possible. Turn a cavity, or make holes, -in the bottom of the under piece, and fill with lead to give weight -and steadiness. This, painted green bronze and varnished, looks neat; -and by having pieces of gutta-percha tubing to fit the shaft, a great -variety of apparatus may be attached to it. - -Again, a “condenser” is often required for the illumination of opaque -objects. My ingenious friend uses an “engraver’s bottle” (price 6d.), -fills it with water, and suspends it betwixt the light and the object. -Where the light is very yellow, he tints the water with indigo, and so -removes the objectionable colour. - -I merely mention these as examples of what may be done by a little -thoughtful contrivance, and to remove the idea that nothing is of -much value save that which is the work of professional workmen, and -consequently expensive. - - - - -CHAPTER II. - -TO PREPARE AND MOUNT OBJECTS “DRY.” - - -The term “dry” is used when the object to be mounted is not immersed -in any liquid or medium, but preserved in its natural state, unless it -requires cleaning and drying. - -I have before stated that thorough cleanliness is necessary in the -mounting of all microscopic objects. I may here add that almost every -kind of substance used by the microscopist suffers from careless -handling. Many leaves with fine hairs are robbed of half their beauty, -or the hairs, perhaps, forced into totally different shapes and groups; -many insects lose their scales, which constitute their chief value to -the microscopist; even the glass itself distinctly shows the marks of -the fingers if left uncleaned. Every object must also be _thoroughly -dry_, otherwise dampness will arise and become condensed in small -drops upon the inner surface of the thin glass cover. This defect is -frequently met with in slides which have been mounted quickly; the -objects not being thoroughly dry when enclosed in the cell. Many of the -cheap slides are thus rendered worthless. Even with every care it is -not possible to get rid of this annoyance occasionally. - -For the purpose of mounting opaque objects “dry,” _discs_ were at one -time very commonly made use of. These are circular pieces of cork, -leather, or other soft substance, from one-quarter to half inch in -diameter, blackened with varnish or covered with black paper, on which -the object is fixed by gum or some other adhesive substance. They are -usually pierced longitudinally by a strong pin, which serves for the -forceps to lay hold of when being placed under the microscope for -examination. Sometimes objects are affixed to both sides of the disc, -which is readily turned when under the object-glass. The advantage of -this method of mounting is the ease with which the disc may be moved, -and so present every part of the object to the eye save that by which -it is fastened to the disc. On this account it is often made use of -when some particular subject is undergoing investigation, as a number -of specimens may be placed upon the discs with very little labour, -displaying all the parts. But where exposure to the atmosphere or small -particles of dust will injure an object, no advantage which the discs -may possess should be considered, and an ordinary covered cell should -be employed. Small pill-boxes have been used, to the bottom of which a -piece of cork has been glued to afford a ground for the pin or other -mode of attachment; but this is liable to _some_ of the same faults as -the disc, and it would be unwise to use these for permanent objects. - -Messrs. Smith and Beck have lately invented, and are now making, a -beautiful small apparatus, by means of which the disc supporting the -object can be worked with little or no trouble into any position that -may prove most convenient, whilst a perforated cylinder serves for the -reception of the discs when out of use, and fits into a case to protect -them from dust. A pair of forceps is made for the express purpose of -removing them from the case and placing them in the holder. - -All dry objects, however, which are to be preserved should be mounted -on glass slides in one of the cells (described in Chapter I.) best -suited to them. Where the object is to be free from pressure, care -must be taken that the cell is deep enough to ensure this. When the -depth required is but small, it is often sufficient to omit the card, -leather, or other circles, and with the “turn-table” before described, -by means of a thick varnish and camel-hair pencil, to form a ring -of the desired depth; but should the varnish not be of sufficient -substance to give such “walls” at once, the first application may be -allowed to dry, and a second made upon it. A number of these may be -prepared at the same time, and laid by for use. When liquids are used -(see Chapter IV.), Dr. Carpenter recommends gold-size as a good varnish -for the purpose, and this may be used in “dry” mountings also. I have -used the asphaltum and india-rubber (mentioned in Chapter I.), and -found it to be everything I could wish. The cells, however, must be -_thoroughly dry_, and when they will bear the heat they should be baked -for an hour at least in a tolerably cool oven, by which treatment the -latter becomes a first-rate medium. All dry objects which will not bear -pressure must be firmly fastened to the slide, otherwise the necessary -movements very often injure them, by destroying the fine hairs, &c. -For this purpose thin varnishes are often used, and will serve well -enough for large objects, but many smaller ones are lost by adopting -this plan, as for a time, which may be deemed long enough to harden -the varnish, they exhibit no defect, but in a while a “wall” of the -plastic gum gathers around them, which refracts the light, and thus -leads the student to false conclusions. In all _finer_ work, where it -is necessary to use any method of fixing them to the slide, a solution -of common gum, with the addition of a few drops of glycerine (Chapter -I.), will be found to serve the purpose perfectly. It must, however, -be carefully filtered through blotting paper, otherwise the minute -particles in the solution interfere with the object, giving the slide a -dusty appearance when under the microscope. - -When mounting an object in any of these cells, the glass must be -thoroughly cleaned, which may be done with a cambric handkerchief, -after the washing mentioned in Chapter I. _If the object be large_, -the point of a fine camel-hair pencil should be dipped into the gum -solution, and a minute quantity of the liquid deposited in the cell -where the object is to be placed, but not to cover a greater surface -than the object will totally hide from sight. This drop of gum must be -allowed to dry, which will take a few minutes. Breathe then upon it two -or three times, holding the slide not far from the mouth, which will -render the surface adhesive. Then draw a camel-hair pencil through the -lips, so as to moisten it slightly (when anything small will adhere to -it quite firmly enough), touch the object and place it upon the gum in -the desired position. This must be done immediately to ensure perfect -stability, otherwise the gum will become at least partially dry and -only retain the object imperfectly. - -When, however, the objects are so minute that it would be impossible to -deposit atoms of gum small enough for each one to cover, a different -method of proceeding must be adopted. In this case a small portion of -the same gum solution should be placed upon the slide, and by means -of any small instrument--a long needle will serve the purpose very -well--spread over the surface which will be required. The quantity thus -extended will be very small, but by breathing upon it may be prevented -drying whilst being dispersed. This, like the forementioned, should be -then allowed to dry; and whilst the objects are being placed on the -prepared surface, breathing upon it as before will restore the power of -adherence. - -When gum or other liquid cement has been used to fix the objects to -the glass, the thin covers must not be applied until the slide has -been _thoroughly dried_, and all fear of dampness arising from the use -of the solution done away with. Warmth may be safely applied for the -purpose, as objects fastened by this method are seldom, if ever, found -to be loosened by it. As objects are met with of every thickness, the -cells will be required of different depths. There is no difficulty in -accommodating ourselves in this--the deeper cells may be readily cut -out of thick leather, card, or other substance preferred (as mentioned -in Chapter I.). Cardboard is easily procured of almost any thickness; -but sometimes it is convenient to find a thinner substance even than -this. When thin glass is laid upon a drop of any liquid upon a slide, -every one must have observed how readily the liquid spreads betwixt -the two: just so when any thin varnish is used to surround an object -of little substance, excessive care is needed lest the varnish should -extend betwixt the cover and slide, and so render it worthless. The -slightest wall, however, prevents this from taking place, so that a -ring of common paper may be used, and serve a double purpose where the -objects require no deeper cell than this forms. - -Many objects, however, are of such tenuity--as the leaves of many -mosses, some of the Diatomaceæ, scales of insects, &c.--that no cell is -requisite excepting that which is necessarily formed by the medium used -to attach the thin glass cover to the slide; and where the slide is -covered by the ornamental papers mentioned in Chapter I., and pressure -does not injure the object, even this is omitted, the thin glass being -kept in position by the cover; but slides mounted in this manner are -frequently injured by dampness, which soon condenses upon the inner -surfaces and interferes both with the object and the clearness of its -appearance. - -The thin glass, then, is to be united to the slide, so as to form a -perfect protection from dust, dampness, or other injurious matter, -and yet allow a thoroughly distinct view of the object. This is to be -done by applying to the glass slide round the object some adhesive -substance, and with the forceps placing the thin glass cover (quite dry -and clean) upon it. A gentle pressure round the edge will then ensure -a perfect adhesion, and with ordinary care there will be little or no -danger of breakage. For this purpose gold-size is frequently used. The -asphalt and india-rubber varnish also will be found both durable and -serviceable. Whatever cement may be used, it is well to allow it to -become in some measure “fixed” and dried; but where no cell or “wall” -is upon the slide, this is _quite necessary_, otherwise the varnish -will be almost certain to extend, as before mentioned, and ruin the -object. It may be stated here that gold-size differs greatly in its -drying powers, according to its age, mode of preparation, &c. (Chapter -IV.) - -Should any object be enclosed which requires to be kept flat during -the drying of the cement, it will be necessary to use some of the -contrivances mentioned in Chapter I. - -When the slide is thus far advanced, there remains the “finishing” -only. Should the student, however, have no time to complete his work -at once, he may safely leave it at this stage until he has a number -of slides which he may finish at the same time. There are different -methods of doing this, some of which may be here described. - -If ornamental papers are preferred, a small circle must be cut out -from the centre a little less than the thin glass which covers the -object. Another piece of coloured paper is made of the same size, and -a similar circle taken from its centre also, or both may be cut at the -same time. The slide is then covered round the edges with paper of any -plain colour, so that it may extend about one-eighth of an inch over -the glass on every side. The ornamental paper is then pasted on the -“object” surface of the glass, so that the circle shows the object as -nearly in the centre as possible, and covers the edges of the thin -glass. The other coloured paper is then affixed underneath with the -circle coinciding with that above. And here I may observe, that when -this method is used there is no necessity for the edges of the slide to -be “ground,” as all danger of scratching, &c., is done away with by the -paper cover. - -Many now use paper covers, about one and a half inches long, on the -upper side of the slide only, with the centre cut out as before, with -no other purpose than that of hiding the edge of the thin glass where -it is united to the slide. - -The method of “finishing,” however, which is mostly used at the present -time, is to lay a coating of varnish upon the edge of the thin glass, -and extend it some little way on the slide. When a black circle is -required, nothing serves the purpose better than the gold-size and -lamp-black, or the asphalt and india-rubber varnish, neither of which -is liable to chip; but when used for this, the latter should be rather -thinner, as before advised. Some of these varnishes are preferred of -different colours, which may be made by using the different kinds of -sealing-wax, as described in Chapter I.; but they are always liable -to the defects there mentioned. This circle cannot be made in any -other way but by one of those contrivances which have now centred in -Shadbolt’s turntable. A very little practice will enable the young -student to place his slide so that the circle may be uniform with the -edge of the thin glass. - -The slide is now complete, except the addition of the name and any -other particulars which may be desirable. For this purpose one of the -methods described in Chapter I. must be employed. - -Amongst the various classes of microscopic objects now receiving -general attention, the Diatomaceæ may be placed in a prominent -position. They afford endless opportunities of research, and some -very elaborate works have already been issued concerning them. -Professor Smith’s may be mentioned as one containing, perhaps, the -best illustrations. The young student may wish to know what a diatom -is. The “Micrographic Dictionary” gives the following definition:--“A -family of confervoid Algæ, of very peculiar character, consisting of -microscopic brittle organisms.” They are now looked upon by almost all -of our scientific men as belonging to the _vegetable_ kingdom, though -some few still assign them to the animal. They are almost invariably -exceedingly small, so that the unaided eye can perceive nothing on -a prepared slide of these organisms but minute dust. Each separate -portion, which is usually seen when mounted, is termed a “frustule,” -or “testule:” this consists of two similar parts, composed of silica, -between and sometimes around which is a mass of viscid matter called -the “endochrome.” They are found in almost every description of water, -according to the variety: some prefer sea-water, others fresh, and -many are seen nowhere but in that which is a mixture of both, as the -mouths of rivers, &c. Ditches, ponds, cisterns, and indeed almost every -_reservoir_, yield abundance of these forms. They are not, however, -confined to “present” life; but, owing to the almost indestructible -nature of their siliceous covering, they are found in a fossil state -in certain earths in great abundance, and are often termed “fossil -Infusoria.” Upon these frustules are generally to be seen lines, -or “markings,” of different degrees of minuteness, the delicacy of -which often serves the purpose of testing the defining power of the -object-glasses. Some of the frustules are triangular, others circular, -and, indeed, of almost every conceivable shape, many of them presenting -us with exquisitely beautiful designs. - -The markings, however, are seldom seen well, if at all, until the -frustules are properly prepared, the different methods of accomplishing -which will be given a little further on. - -The _collection_ of the fresh diatoms is so closely connected with -their _preservation_, that a few notes may be given upon it before we -pass on. For this purpose a number of small bottles must be provided, -which may be placed in a tin box, with a separate apartment for each, -so that all chance of breakage may be done away with. The diatoms -are generally of a light brown colour; and where they are observed -in the water, the bottle may be so placed, with the mouth closed by -the finger, that when the finger is withdrawn the water will rush in, -carrying the diatoms also. If they are seen upon plants, stones, or -any other substance, they may generally be detached and placed in the -bottle. When there is a green covering upon the surface of the water, a -great quantity of diatoms is usually found amongst it; as also upon the -surface of the mud in those ponds where they abound. In these cases, a -broad flat spoon will be found very useful, and one is now made with a -covering upon the broader portion of it to protect the enclosed matter -from being so readily carried off whilst bringing it to the surface -again. Where there is any depth of water, and the spoon will not reach -the surface of the mud, the bottle must be united to a long rod, and -being then carried through the upper portion with the mouth downwards, -no water will be received into it; but on reaching the spot required, -the bottle-mouth may be turned up, and thus become filled with what is -nearest. - -From the stomachs of common fish--as the cod, sole, haddock, &c.--many -specimens of Diatomaceæ may be obtained, but especially from the crab, -oyster, mussel, and other shell-fish. Professor Smith states that from -these curious receptacles he has taken some with which he has not -elsewhere met. To remove them from any of the small shell-fish, it is -necessary to take the fish or stomach from the shell, and immerse it -in strong hot acid (nitric is the best) until the animal matter is -dissolved, when the residue must be washed and treated as the ordinary -Diatomaceæ hereinafter described. - -Many diatoms are seen best when mounted in a dry state, the minute -markings becoming much more indistinct if immersed in liquid or balsam; -and for this reason those which are used as test objects are usually -mounted _dry_. Many kinds also are now prepared in this way, as opaque -objects to be examined with the lieberkuhn, and are exquisitely -beautiful. Others, however, are almost invariably mounted in balsam; -but as these will be again referred to in Chapter III., and require -the same treatment to fit them for the slide, it will not be out of -place to describe the cleaning and preparation of them here. As before -stated, there is much matter surrounding them which must be got rid of -before the “_siliceous_ covering” can be shown perfectly. As, however, -we may first wish to become acquainted in some degree with what we have -to do, it is well to take a small piece of _talc_, and place a few of -the diatoms upon it. This may be held over the flame of the spirit-lamp -until all the surrounding matter is burnt away, and a tolerable idea -may be thus obtained as to the quality of our treasure. - -In some cases it is well to use this burning operation alone in -_mounting_ specimens of diatoms, when they may be placed in their -natural state upon the thin glass, burnt for awhile upon the platinum -plate, hereafter described, and mounted dry or in balsam. - -In the preparation and cleaning of Diatomaceæ, there is little -satisfaction unless these operations have been successfully performed, -as a very small portion of foreign matter seriously interferes with -the object. The mode of preparing them varies even amongst the most -experienced. It will be found, therefore, most satisfactory to examine -the principal of these separately, although it may be at the risk of -some little repetition. - -The method which is the most frequently made use of is the -following:--Place the “gathering” containing the Diatomaceæ in a small -glass or porcelain vessel, add strong nitric acid, and, by the aid -of Bunsen’s burner or spirit-lamp, boil for some minutes. From time -to time a drop of the mixture may be put upon a slide, and examined -under the microscope to see if all foreign matter be got rid of. When -the valves are clean, the vessel containing them must be filled with -water, and the whole left for an hour or two, so that all the diatoms -may settle perfectly. The liquid must then be poured off carefully, -or drained away by the aid of a syphon, so that none of the diatoms -are removed with it. Indeed, it is well to examine the liquid drained -off each time with the microscope, as the finer forms are frequently -lost in the washings. The vessel must then be refilled with pure -water, allowed to settle, and drained as before. This washing must be -repeated until a drop being placed upon a slide and evaporated leaves -no crystals. When it is desirable to preserve the diatoms in this state -before mounting (which process will be described in another place), -they may be placed in a small phial with a little distilled water. - -There are many cases in which the above method will not effect a -_perfect_ cleansing, as certain substances with which the diatoms are -frequently mixed are not soluble in _nitric acid_. For this reason -the following method is resorted to:--Take a quantity of the matter -containing the Diatomaceæ and wash first with pure water, to get rid of -all the impurities possible. Allow this to settle perfectly and decant -the water. Add hydrochloric acid gradually, and when all effervescence -has subsided, boil for some minutes by aid of the lamp. When cool and -the particles have subsided, decant the hydrochloric and add nitric -acid. The boiling must then be repeated until a drop of the liquid when -placed under the microscope shows the valves or “frustules” clean. -After allowing the diatoms to settle, the acid must be decanted, and -pure water substituted. The washing must be repeated as in the former -process until all the remains of crystals or acid are removed, when the -specimens may be preserved in small phials as stated above. - -Such are the usual modes of treating the Diatomaceæ, but there are -certain cases in which particular methods are required to give anything -like perfect results. Persons of great experience combine a variety of -treatments, and thus obtain better and more uniform specimens. Perhaps -it will be advantageous to give the young student the process adopted -by one of the most successful preparers of these objects; but I will -first state the different methods of mounting the cleaned diatoms dry: -how to employ Canada balsam and fluid in their preservation will be -elsewhere described. - -It was before stated that the diatoms when cleansed might be preserved -in small phials of distilled water. When required for mounting, shake -the phial, and with a thin glass tube or rod take up a drop of the -fluid and spread it upon the surface of the slide in the desired -position. This must then be allowed to dry gradually, or by the aid -of the lamp if necessary, without being shaken or interfered with, -otherwise uniformity of dispersion will be prevented. When _thoroughly_ -dry, a thin ring of one of the adhesive varnishes--gold-size will be -found as good as any--may be drawn round the diatoms, and allowed to -dry in a slight degree. The slide and thin glass cover should then be -warmed and the latter gently pressed upon the ring of varnish until the -adhesion all round is complete. - -As some of the diatoms require object-glasses of extremely high power, -and, consequently, short focus, to show them, they must be as close to -the outer surface of the cover as possible. For this reason they are -sometimes placed upon the under side of the thin glass, as follows. -Clean the surfaces of the slide and cover, and with the rod or pipe -place the liquid containing the diatoms upon the thin glass, and dry as -before. Trace the ring to receive the cover upon the slide, and when -almost dry, warm both and proceed as above. Whichever of these methods -is employed, the outer ring of coloured varnish may be applied as -elsewhere described and the slide finished. - -The diatoms are also sometimes mounted betwixt two thin glasses, as -described in Chapter I., so that the light by which they are examined -may receive as little interference as possible, and that an achromatic -condenser may be brought into focus under the slide. - -Of the various modes of cleaning and mounting the Diatomaceæ, I believe -that the following may be safely recommended as affording results of -the very best quality. My friend, Mr. T. G. Rylands, gave it to me as -that which he prefers, and I can safely say that his numerous slides -are at least equal to any I have ever seen. I will give it just as I -received it from him, though there may be some little repetition of -what has been said elsewhere, as he does not appropriate any part of it -as his own. He says:--In this branch of mounting, general rules alone -can be laid down, because the gatherings may contain iron, lime, fine -silt, or vegetable matter under conditions for special treatment, and -consequently the first step should be to experiment on various kinds. - -In gathering diatoms much labour is saved by judgment and care; -hence it is desirable to get acquainted with them in their growing -condition, so that when recognised upon the sands or other spots they -may be carefully removed by the aid of the spoon or small tin scoop -before described. When growing upon algæ or other plants, the plants -and diatoms together may be carried home, in which case they must be -simply drained and not washed or pressed, in order that the diatoms -be not lost. As it is always desirable to examine the gathering on -the ground, a “Gairdner’s hand microscope” with powers from 80 to 200 -diameters will be found very useful. The best gatherings are those -which represent one species abundantly. Those which are mixed may -be rejected, unless they are seen to contain something valuable or -important, as the object should be not so much to supply microscopical -curiosities as to collect material which is available for the study of -nature. - -The gathering when carried home should always be carefully examined -before anything is done with it; not only on account of the additional -information thus acquired, but also because it often happens that a -specimen should be mounted in fluid (see Chapter IV.) in the condition -in which it is gathered, as well as cleaned and mounted in balsam -(Chapter III.) and dry. - -Where the gathering is taken from sand, the whole may be shaken up -in water as a preliminary operation, when much of the sand will -be separated by its own weight. The lime test, however, should be -applied, viz.--a small portion of hydrochloric acid, and if there be -effervescence it must be dissolved out by this means. From Algæ and -other weeds diatoms may be detached by agitating the whole together in -a weak solution of nitric acid--about one of pure acid to twenty or -thirty of water, as it must be sufficiently weak to free the diatoms -without destroying the matter to which they adhere. The diatoms -may then be separated by sifting through coarse muslin, which will -retain the Algæ, &c. The process of cleaning will vary according to -circumstances. Some gatherings require to be boiled only a few minutes -in nitric acid; but the more general plan where they are mixed with -organic or other foreign matter, is to boil them in pure sulphuric -acid until they cease to grow darker in colour (usually from a half -to one minute), and then to add, drop by drop to avoid explosions, -a cold saturated solution of chlorate of potash until the colour is -discharged, or, in case the colour does not disappear, the quantity -of the solution used is at least equal to that of the acid. This -operation is best performed in a wide-mouthed ordinary beaker glass,[B] -a test-tube being too narrow. The mixture whilst boiling should be -poured into thirty times its bulk of cold water, and the whole allowed -to subside. The fluid must then be carefully decanted and the vessel -re-supplied once or twice with pure water, so as to get rid of all the -acid. The gathering may then be transferred to a small boiling glass -or test-tube, and--the water being carefully decanted--boiled in the -smallest available quantity of nitric acid, and washed as before. This -last process has been found necessary from the frequent appearance of -minute crystals, which cannot otherwise be readily disposed of without -the loss of a considerable proportion of diatoms. - - [B] These glasses are round, about six inches high, and usually - contain about eight ounces. They are rather wider at the - bottom, tapering gradually to the top, and may be generally - procured at the chemists, &c. - -I may here mention that the washing glasses used by Mr. Rylands are -stoppered conical bottles varying in capacity from two ounces to one -quart; the conical form being employed to prevent the adherence of -anything to the side; they are “stoppered” to render them available in -the shaking process about to be described. - -The gathering, freed from acid, is now put into two inches depth of -water, shaken vigorously for a minute or two, and allowed to subside -for half an hour, after which the turbid fluid must be carefully -decanted. This operation must be repeated until all the matter is -removed which will not settle in half an hour. The fluid removed should -be examined by a drop being put upon a slide, as in some cases very -light diatoms have been found to come off almost pure in one or more of -these earlier washings. The quantity of water and time of subsidence -given may be taken generally, but may require to be modified according -to circumstances and the judgment of the operator. By the repetition -and variation of this process--the _shaking_ being the most important -part--the gathering, if a _pure_ one, will be sufficiently clean. If, -however, it contains a variety of species and forms, it may require to -be divided into _different densities_. - -In some cases, however, it is best to divide the gathering as a -_preliminary_ operation, which may be done by agitating it in a -quantity of water and decanting what does not readily subside. The -heavier and the lighter portions are then to be treated as two -separate boilings. But when the cleansing has been carried to the -above stage and this division is required, the plan must be somewhat -as follows:--The gathering must be shaken in a test-tube with six -inches of water, and then allowed to subside until one inch at the top -remains pure. About three inches are then to be carefully withdrawn by -a pipette, when the tube may be filled up and the operation repeated. -The three lower inches also may then be decanted and examined. The -gathering is thus divided into three portions, viz.--that which was -withdrawn by the pipette, that which remained floating in the lower -three inches of water in the tube, and that which had settled at the -bottom. An examination of these will inform the operator how to obtain -that particular density of gathering which he desires, and how far it -is worth while to refine this process of elutriation; for in cases of -necessity any one, or all three, of these densities may be operated -upon in the same way to separate a particular diatom. - -As occasional aids, it may be remarked, that in some cases _liquor -ammoniæ_ may be used in place of water, as it often separates fine -dirt, which is not otherwise easily got rid of. Some fossil deposits -require to be treated with a boiling solution of carbonate of soda to -disintegrate them; but this operation requires great care, lest the -alkali should destroy the diatoms. Vegetable silicates also sometimes -require to be removed by a solution of carbonate of soda; but as the -frustules of the diatoms themselves are but _vegetable silica_, even -more care is required in this case. It may be well to mention, that -some diatoms are so imperfectly siliceous that they will not bear -_boiling_ in acid at all. Some of these may be allowed to stand in cold -nitric acid some time, whilst others of a smaller and more delicate -character should, when possible, be treated with distilled water alone. - -We will now consider the mode of mounting the prepared diatoms, which, -if used dry (as described in this chapter), should be carefully washed -two or three times with the purest distilled water. In this branch, -as in every other, each collector gives preference to that method in -which he is an adept. Thus the diatoms may be placed on the under side -of the cover, to be as near to the object-glass as possible, or upon -the slide itself; and each plan has its advocates. Whichsoever of these -is used, nothing seems more simple to the novice than a tolerably -equal dispersion of the objects upon the slide or cover; but this is -by no means so readily accomplished, consequently I give Mr. Rylands’ -method, as his slides are perfect in this respect also. He always -places the diatoms upon the thin glass cover. It is not sufficient, -as is frequently thought, to take a drop of liquid containing the -cleansed material and spread it upon the cover or slide, as without -some additional precaution that uniform and regular distribution of the -specimens is not obtained which is desirable. In order to effect this, -let a drop of the cleansed gathering be diluted sufficiently for the -purpose--how much must be determined in each case by experiment--and -let the covers to be mounted be cleaned and laid upon the brass plate. -(See Chapter I.) By means of a glass tube, about one-twelfth of an -inch in diameter, stopped by the wetted finger at the upper end, take -up as much of the diluted material as will form a moderately convex -drop extending over the whole cover. When all the covers required are -thus prepared, apply a lamp below the brass plate, and raise the -temperature to a point just short of boiling. By this means the covers -will be dried in a few minutes, and the specimens equally distributed -over the whole area. The spread of the fluid upon the covers is -facilitated by breathing upon them; and, to insure uniformity, care -must be taken to avoid shaking them whilst drying. The best plan is to -mount at least half a dozen at once. - -Before mounting, Mr. Rylands always burns the diatoms upon the glass -at a dull red heat, whether they are used with balsam or dry. This -burning, he says, is not only an additional cleaning process, but -it effectually fixes the diatoms, and prevents them floating out if -mounted with balsam. The thinnest covers may be burnt without damage -if they are placed upon a small piece of platinum foil of the size -required, which should be about one-hundredth of an inch thick, -perfectly flat, and having three of its edges slightly bent over, so as -to prevent its warping with the heat. The small flame of a spirit-lamp, -or, where there is gas, a Bunsen’s burner, may be employed. The cover -should be shaded from direct daylight, that the action of the flame -may be observed more perfectly. Care must then be taken to raise the -temperature only to the dull red heat before mentioned. The cover will -then be in a fit state for mounting as required. - -It has been stated in another place that it is assumed the operator is -not mounting diatoms simply as microscopic objects, but as instructive -specimens. It is not, therefore, sufficient to take a single slide as -all that is required, but to have the same diatom prepared in as many -ways as possible. The following are the principal:-- - - 1. Mounted crude in fluid (see Chapter IV.). - - 2. Burnt crude upon the cover, and mounted dry or in balsam (as - before mentioned). - - 3. Mounted dry or in balsam (see Chapter III.), after the - cleansing process already described. - -I will here give Mr. Rylands’ method of mounting them _dry_, the fluid -and balsam preparations being noticed in their respective chapters. -The slide with the ring of asphalt, or black varnish, should have been -prepared some weeks previously, in order to allow it to dry thoroughly. -When required, it must be held over the spirit-lamp or Bunsen’s burner -until the ring of varnish is softened. The burnt cover, having been -heated at the same time, must then be taken in the forceps and pressed -upon the softened varnish until it adheres all round. When cold, an -outer ring of asphalt completes the slide. - -Such is the method which my friend Mr. T. G. Rylands employs in -the preparation of diatoms for the microscope. I have said enough -concerning his results. It is to be feared, however, that to some these -several modes of operation may appear lengthy and complicated; but if -read carefully, and the experiments tried, they will be found simple -enough in practice, and to occupy much less time than an intelligible -description would lead the novice to believe necessary. - -One of the most fertile as well as the most curious magazines of -Diatomaceæ is _guano_. The siliceous forms contained therein have been -devoured by sea-birds and passed through the stomach uninjured, and -after lying for ages may be cleaned and classified. Many of these are -not elsewhere met with, so that the student who is desirous to enter -into the study of Diatomaceæ must be instructed as to the best mode -of obtaining them from this source. The particulars to be observed -so closely resemble those before mentioned in the treatment of the -ordinary diatoms, that it will be sufficiently explicit to give the -outlines of the process. The guano must be first washed in pure water, -allowed to subside perfectly, and the liquid then poured off. This must -be repeated until the top fluid is clear, and care taken not to decant -the liquid until perfect subsidence has taken place. The deposit must -then be treated with hydrochloric acid with a gentle heat for an hour -or two, adding a little fresh acid at intervals as long as it excites -any effervescence After this nitric acid must be substituted for the -hydrochloric, and the heat kept up to almost boiling-point for another -hour at least, adding a little fresh acid as before. When this ceases -to act, the deposit must be allowed to settle perfectly and the acid -poured off. All traces of the acid must now be washed away with pure -water, when the remains will be Diatomaceæ, the sand contained in the -guano, and a few other forms. Some of these may be mounted dry, as -before mentioned, but the greater portion should be put up in Canada -balsam as described in Chapter III. - -Such is the ordinary method for the treatment of guano; but Mr. -Rylands’ mode of proceeding with ordinary Diatomaceæ (before given) -will be found equally successful with these deposits. - -The fossil Infusoria (as they were formerly called) are now termed -Diatomaceæ, and are found in various parts of the world--“Bermuda -earth,” “Berg-mehl” from Norway, deposit from Mourne Mountain in -Ireland, &c. They are found in immense quantities, and afford the -microscopist innumerable objects. The same treatment as that usually -employed for the Diatomaceæ must be followed with these deposits, but -as they are sometimes obtained in hard masses, disintegration is first -necessary. To effect this, they are usually boiled for a short time in -diluted _liquor potassæ_, which will soon cause the mass to fall into a -mud-like deposit. Water must then be immediately added, in order that -all further action of the _liquor potassæ_ may be stopped, otherwise -the objects searched for will be dissolved. For this reason it is -necessary to understand what substance is being dealt with, because -some deposits are much finer and acted upon more readily than others. - -In mounting these objects, some are so delicate that they are almost -invisible when balsam is used with them; they are therefore usually -mounted _dry_. Others, however, are much coarser, and may be mounted in -balsam like the Diatomaceæ mentioned in Chapter III. - -The common Infusoria cannot be mounted dry with any great success, -though a few may be placed upon the glass slide and allowed to dry -naturally, when their characters will be very well shown. To obtain -anything like a natural appearance, they must be put up in fluid as in -Chapter IV. - -Next to the Diatomaceæ, no class of microscopic objects has been more -looked into of late than the Foraminifera. These animals are almost -all marine, having a jelly-like body enclosed in one or more chambers -of shell generally composed of carbonate of lime. The shells are made -with minute orifices, through which the pseudopodia (false feet) are -extended by which the animal is enabled to lay hold of anything and -draw itself along. From the possession of these orifices they derive -their name, as _foramen_ means a door or opening. They have been found -in every depth of sea hitherto sounded, each depth being abundant in -certain species; the lowest beds containing the greatest number of -specimens, though with less variation of kinds. In chalk they are found -in a fossil state, and may readily be shown (see Chapter III.); in -limestone and other hard stones they are abundant, and some mountains -are composed principally of these shells. - -The methods of obtaining Foraminifera are various. Many may be found -upon seaweeds, which should always be examined as soon as possible -after gathering. They are found in masses upon some coasts where the -waves have carried and left them; but they are to be found the most -abundantly in sand or mud dredged from the bottom of the sea. They -must, however, be cleansed and separated from the mass of impurity -with which they are usually mixed. This may be done in various ways, -according to the nature of the accompanying matter. If sand alone, as -is frequently the case, the whole mass must be _thoroughly_ dried, and -then stirred up in clean water. The sand will soon subside by its own -weight, but the chambers of the Foraminifera, being filled with air, -will float upon the surface, and may be skimmed off. There is, however, -one objection to this mode of proceeding--some of these objects are -so minute, the chambers containing comparatively so small a quantity -of air, that they sink and are cast away with the refuse sand. On this -account it is preferable to take the trouble of searching certain -soundings under the microscope, using the camel-hair pencil, or some -other contrivance before mentioned, to extract those objects which -are required. To clean the Foraminifera, Professor Williamson advises -to transfer the specimens to an evaporating dish containing a weak -solution of caustic potash. This must be boiled for “some moments,” -when the organic matter will be entirely dissolved, and the calcareous -shells left free from impurity. They must now be well washed in water, -so that all alkaline matter may be entirely got rid of. - -If the specimens are in _mud_, we must proceed in a different -way:--Stir up the whole mass in water, and allow it to stand until the -heavier portion has sunk to the bottom; the water may then be poured -off and examined to see if there are any objects contained in it. -This process must be repeated until the water comes off quite clear, -when (if the search is for Foraminifera only) the solution of caustic -potash may be used as before mentioned. However the soundings, &c., are -cleaned, it is necessary to assort them under the microscope with the -camel-hair pencil or other contrivance, as it is impossible to obtain -them fit for mounting without undergoing this process. - -The sea soundings taken by order of Government are drawn from the -bottom in a kind of apparatus ingeniously made for the purpose, and -the sand, mud, &c., are brought up in their original state. Common -soundings, however, are taken by lowering a heavy piece of lead coated -with tallow, which consequently brings up a small portion of the -matter from the bottom. Mr. George Mosley, the late Secretary of the -Manchester Microscopic Society, obtained numbers of the “scrapings” -from the sounding leads. To make any use of these it is, of course, -necessary to free them from all traces of the tallow. Mr. Dancer -places the sounding in a basin and pours boiling water upon it, which -causes the melted grease to rise to the surface. When cold, this may -be removed, and the water carefully decanted. The operation may be -repeated until no grease appears, when the water may be withdrawn -and _liquor ammoniæ_ used, which will form a soapy solution with any -remaining grease. This must be treated with hot water for the final -washing. Care must be taken lest the finer forms be carried away in -decanting the washing liquid. Should it be wished to make certain as -to this point, each washing should be examined under the microscope. -In some cases the process of Mr. Dancer will prove sufficient. Mr. -Dale, however, gives a method of accomplishing the same result, which -is much more readily completed; and as the results cannot be found -fault with, I will here give it in full:--It is now well known that one -of the products obtained from the naphtha of coal-tar is a volatile, -oily substance, termed _benzole_ (or, by French chemists, _benzine_), -whose boiling-point, when pure, is about 180° Fahrenheit, which is a -perfect solvent for fatty substances. In a capsule, previously warmed -on a sand-bath, Mr. Dale mixes with the tallow soundings benzole, -whose boiling-point may be about 200°, until sufficiently diluted so -as to run freely, pressing the lumps with a glass rod until thoroughly -mingled; the solution and its contents are then poured into a paper -filter, placed in a glass funnel; the capsule is again washed with -benzole, until the whole of the gritty particles are removed into -the filter. A washing-bottle is then supplied with benzole, and the -contents of the filter washed to the bottom until that liquid passes -off pure, which may be tested by placing a drop from the point of the -funnel on a warm slip of glass or bright platinum, when, if pure, -the benzole will evaporate without residue or tarnish; if grease be -present, the washings must be continued until they are free from it. -After rinsing through _weak_ acid, or alcohol, for final purification, -the calcareous forms will be ready for mounting. - -The filter and its contents may be left to dry spontaneously, when the -latter can be examined by the microscope. Should time be an object, -rapid drying may be effected by any of the usual methods; one of -which, recommended by Mr. Dale, is to blow a stream of hot air through -a glass tube held in the flame of a Bunsen’s burner. The lower the -boiling-point of the benzole, the more readily can the specimens be -freed from it. A commoner quality may be used, but it is more difficult -to dry afterwards. - -Pure benzole being costly, this may appear an expensive process; but, -with the exception of a trifling loss by evaporation, the whole may be -recovered by simple distillation. The mixture of tallow and benzole -being placed in a retort in a hot-water, a steam, or a sand bath, the -benzole will pass into the receiver, and the tallow or other impurities -will remain in the retort. When the whole of the benzole has distilled -over, which is ascertained by its ceasing to drop from the condenser, -the heat is withdrawn and the retort allowed to cool before the -addition of fresh material. Half a dozen to a dozen filters, each with -its specimen, can be in process at the same time; and the distillation -of the recovered benzole progresses as quickly as the filtration, which -was practically proved on the occasion named. Great caution in the use -of benzole is to be taken in the approach of lights to the inflammable -vapour. - -After the Foraminifera and calcareous forms have been removed, the -residue may be treated with acids and levigation in the usual manner, -to obtain siliceous forms and discs, if there are any present; but to -facilitate their deposition, and to avoid the loss of any minute atoms -suspended in the washings, I would suggest the use of filtration. The -conical filter is unsuitable, as the particles would spread over too -great a surface of paper; but glass tubes open at both ends (such as -broken test-tubes) will be found to answer, the broad end covered -with filtering paper, and over that a slip of muslin tied on with a -thread to facilitate the passage of the water and prevent the risk of -breaking the paper. Suspend the tube over a suitable vessel through a -hole cut in thin wood or cardboard, pour in the washings which can be -thus filtered and then dried. The cloth must be carefully removed, the -paper cut round the edges of the tube, and the diatoms on the paper -disc may be removed by a camel-hair pencil or otherwise, ready for -mounting. Thus many objects may be preserved which would be either -washed away or only be obtained by a more tedious process. - -Such is Mr. Dale’s method of cleaning the soundings from the tallow, -and as it thoroughly accomplishes its end, and is alike effective -and not injurious to Foraminifera and diatoms, it may be safely -recommended. The weak solution of caustic potash before advised for -Foraminifera, must not be used where it is desired to preserve the -diatoms, as they would certainly be injured, or destroyed altogether, -if this agent were employed. - -In fixing the Foraminifera upon the slide, no better plan can be -followed than the “dry cells” and gum recommended in the early parts -of this chapter. Owing to their thickness and composition, most of -them are opaque objects only; but they are exquisitely beautiful, -and require no particular care, except in allowing the cell, &c., to -be perfectly dry, when the cover is placed upon it, or the damp will -certainly become condensed upon the inner side, and the examination -seriously interfered with. - -Many of the Foraminifera require cutting into sections if it is -wished to examine the internal structure, &c.,--“decalcifying” is -also desirable in some cases;--both of these processes will be found -described at length in the chapter on Sections and Dissection. - -When more than one specimen of some particular shell is obtained, it is -better to place them upon the slide in different positions, so as to -show as much of the structure as possible. I will conclude this subject -by quoting a passage from T. Rymer Jones:--“It is, therefore, by no -means sufficient to treat these shells as ordinary objects by simply -laying them on a glass slide, so as to see them only from one or two -points of view; they must be carefully examined in every direction, -for such is the diversity of form that nothing short of this will be -at all satisfactory. For this purpose, they should be attached to the -point of a fine needle, so that they may be turned in any direction, -and examined by reflected light condensed upon them by means of a -lens or side reflector. In many of the thick-shelled species it will -be necessary to grind them down on a hone [see Chapter V.] before the -number and arrangement of the internal chambers is discernible; and in -order to investigate satisfactorily the minutiæ of their structure, a -variety of sections, made in various ways, is indispensable.” - -Plants afford an almost inexhaustible treasury for the microscope, -and many of them show their beauties best when mounted dry. When any -of these also are to be mounted, care must be taken that they are -thoroughly dry, otherwise the damp will certainly arise in the cell, -and injure the object; and it may be here mentioned that long after a -leaf has every appearance of dryness, the interior is still damp, and -no way can be recommended of getting rid of this by any quicker process -than that effected by keeping them in a warm room, as many leaves, -&c., are utterly spoiled by using a hot iron or other contrivance. The -safest way is to press them gently betwixt blotting-paper, which may -be removed and dried at short intervals; and though this may appear a -tedious operation, it is a _safe_ one. - -On the surface of the leaves, hairs and scales of various and very -beautiful forms are found, most of which display their beauties best -when removed from the leaf, and used with the polarizer. These will be -noticed in another place; but a portion of the leaf should always be -prepared in its natural form, to show the arrangement of the hair or -scales upon it; which must almost invariably be mounted dry when used -for this purpose. Many of them require very delicate handling. The -_epidermis_, or, as it is by some termed, the _cuticle_, is the outer -skin which lies upon the surface of the leaves and other parts of most -plants. This is composed of cells closely connected, often bearing -the appearance of a rude network. In many plants, by scraping up the -surface of the leaf, a thin coating is detached, which may be torn off -by taking hold of it with the forceps. The piece may then be washed and -floated upon a glass slide, where, on drying, it will be firmly fixed, -and may usually be mounted dry. Amongst the most beautiful and easily -prepared of these may be mentioned the petal of the geranium, the cells -of which are well defined and amongst the most interesting. - -Closely connected with the leaves are the ANTHERS and POLLEN, of -which a great number are beautiful and interesting subjects for the -microscopist. - -The mallow tribe will furnish some exquisite objects, bearing the -appearance of masses of costly jewels. These are usually dried with -pressure, but the natural form may be more accurately preserved by -allowing them to dry as they are taken from the flower, with no -interference except thoroughly protecting them from all dust. Sometimes -the anther is divided, so that the cell required to receive them may -be of as little depth as possible. The common mallow is a beautiful -object, but I think the lavatera is a better, as it shows the pollen -chambers well, when dried unpressed. The pollen is often set alone, and -is well worth the trouble, as it then admits of more close examination. -Often it is convenient to have the _anther and pollen_ as seen in -nature on one slide, and the _pollen_ alone upon another. The former -should be taken from the flowers before their full development is -attained, as if overgrown they lose much of their beauty. Some pollens -are naturally so dark that it is necessary to mount them in Canada -balsam or fluid, as described in other places; but they are better -mounted dry when they are not too opaque. - -Here, too, we may also mention the SEEDS of many plants as most -interesting, and some of them very beautiful, objects, requiring for -the greater part but a low power to show them. Most of these are to be -mounted dry, as opaque objects, in cells suited to them, but some are -best seen in balsam, and will be mentioned in Chapter III. - -The CORALLINES, many of which are found on almost every coast, afford -some very valuable objects for the microscope. They must be well washed -when first procured, to get rid of all the salts in the sea-water, -dried and mounted in cells deep enough to protect them from all danger -of pressure, as some of them are exceedingly fragile. The white ivory -appearance which some of them present is given to them by an even -covering of carbonate of lime; and should it be desired to examine the -structure of these more closely, it may be accomplished by keeping them -for some time in vinegar or dilute muriatic acid, which will remove the -lime and allow of the substance being sliced in the same way as other -Algæ. (“Micrographic Dictionary,” p. 183.) - -THE SCALES OF INSECTS.--The fine dust upon the wings of moths and -butterflies, which is so readily removed when handled carelessly, -is what is generally called _scales_. To these the wing owes the -magnificent colours which so often are seen upon it; every particle -being what may be termed a distinct flat feather. How these are placed -(somewhat like tiles upon a roof) may be easily seen in the wing of -any butterfly, a few being removed to aid the investigation. The form -of them is usually that of the “battledore” with which the common game -is played, but the handle or base of the scale is often short, and the -broad part varies in proportionate length and breadth in different -specimens. The markings upon these also vary, some being mostly -composed of lines running from the base to the apex, others reminding -us of network--bead-like spots only are seen in some--indeed, almost -endless changes are found amongst them. These scales are not confined -to butterflies and moths, nor indeed to the _wings_ of insects. The -different gnats supply some most beautiful specimens, not only from -the wings, but also from the proboscis, &c.; whilst from still more -minute insects, as the podura, scales are taken which were at one time -esteemed as a most delicate test. The gorgeous colours which the -diamond beetles also show when under the microscope are produced by -light reflected from minute scales with which the insects are covered. - -In mounting these objects for the microscope it is well to have the -part of the insect from which the scales are usually taken as a -separate slide, so that the natural arrangement of them may be seen. -This is easily accomplished with the wings of butterflies, gnats, &c.; -as they require no extraordinary care. In mounting the _scales_ they -may be placed upon slides, by passing the wings over the surface, or -by gently scraping the wing upon the slide, when they must be covered -with the thin glass. Of course, the extreme tenuity of these objects -does away with the necessity of any cell excepting that formed by the -gold-size or other cement used to attach the cover. The scales of the -podura should be placed upon the slide in a somewhat different manner. -This insect is without wings, and is no longer than the common flea. It -is often found amongst the sawdust in wine-cellars, continually leaping -about by the aid of its tail, which is bent underneath its body. Dr. -Carpenter says:--“Poduræ may be obtained by sprinkling a little oatmeal -on a piece of black paper near their haunts; and after leaving it there -for a few hours, removing it carefully to a large glazed basin, so -that, when they leap from the paper (as they will when brought to the -light), they may fall into the basin, and may thus separate themselves -from the meal. The best way of obtaining their scales, is to confine -several of them together beneath a wine glass inverted upon a piece of -fine smooth paper; for the scales will become detached by their leaps -against the glass, and will fall upon the paper.” These scales are -removed to the slide, and mounted as those from the gnats, &c. When the -podura has been caught without the aid of the meal, it may be placed -upon the slide, under a test-tube, or by any other mode of confinement, -and thus save the trouble of transfer from the paper before mentioned. -Another method is to seize the insect by the leg with the forceps and -drag it across the slide, when a sufficient quantity of scales will -probably be left upon it. - -These scales are usually mounted “dry;” but Hogg recommends the use of -Canada balsam (Chapter III.) as rendering their structure more definite -when illuminated with Wenham’s parabolic reflector. Some advise other -methods, which will be mentioned in Chapter IV. As most _insects_ -when undissected are mounted in Canada balsam, the different modes of -treatment which they require will be stated in another place. - -In mounting blood of any kind to show the corpuscles, or, as they are -often called, _globules_, which are round or oval discs, it is but -necessary to cover the slide on the spot required with a coating as -thin as possible and allow it to dry before covering with the thin -glass. There is a slight contraction in the globules when dried, but -not enough to injure them for the microscope. The shape of these varies -in different classes of animals, but the size varies much more, some -being many times as large as others.--Some of the _larvæ skins_ are -beautiful objects; but, like many sections of animal and other fragile -matter, are difficult to extend upon the slide. This difficulty is -easily overcome by floating the thin object in clear water, immersing -the slide and when the object is evenly spread gently lifting it. Allow -it then to dry by slightly raising one end of the slide to aid the -drainage, and cover with the thin glass as other objects. The tails and -fins of many small fish may be mounted in a similar manner, and are -well worth the trouble. - -A few objects which are best shown by mounting _dry_ may be here -mentioned as a slight guide to the beginner, though some of them have -been before noticed;--many of the Foraminifera as elsewhere described. -Some _crystals_ are soluble in almost any fluid or balsam, and should -be mounted _dry_; a few, however, deliquesce or effloresce, which -renders them worthless as microscopic objects. - -The wings of butterflies and gnats, as before noticed, afford many -specimens wherewith to supply the cabinet of the young student. A -great variety also may be found amongst the ferns; indeed, these alone -will afford the student occupation for a long time. On the under-side -of the leaves are the reservoirs for the “spores,” which in many -instances somewhat resemble green velvet, and are arranged in stripes, -round masses, and other forms. The spores are usually covered with a -thin skin termed the _indusium_, which is curiously marked in some -specimens, often very like pollen-grains. The manner in which these -spores with all their accompaniments are arranged, their changes and -developments afford almost endless subjects for study; different ferns -presenting us with many variations in this respect totally invisible -without the aid of the microscope. The hymenophyllums (of which two -only belong to England) are particularly interesting, and the structure -of the leaves when dried makes them beautiful objects, often requiring -no balsam to aid their transparency. Portions of the _fronds_ of ferns -should be mounted as opaque objects, after having been dried between -blotting paper, when they are not injured by pressure; but care must -be taken to gather them at the right time, as they do not show their -beauty before they are ripe, and if over-ripe the arrangement of the -spores, &c., is altered. The spores may be mounted as separate objects -in the same manner as pollen, before-mentioned, and are exquisitely -beautiful when viewed with a tolerably high power. The number of -foreign ferns now cultivated in this country has greatly widened the -field for research in this direction; and it may also be mentioned -that the under-sides of many are found to be covered with “scales” of -very beautiful forms. A small piece of the frond of one of these may -be mounted in its natural state, but the removal of the “scales” for -examination by polarized light will be described in another place. The -mosses also are quite a little world, requiring but a low power to show -their beauties. The leaves are of various forms, some of which resemble -beautiful net-work; the “urns” or reservoirs for the spores, however, -are perhaps the most interesting parts of these objects, as also of -the “liverworts” which are closely allied to the mosses. These “urns” -are generally covered by lids, which fall off when the fruit is ripe. -At this period they are well fitted for the microscope. The common -screw-moss may be found in great abundance, and shows this denudation -of the spores very perfectly. Many of these may be easily dried without -much injury, but they should also be examined in their natural state. - -The student should not omit from his cabinet a leaf of the nettle and -the allied foreign species, the mystery of which the microscope will -make plain. The hairs or stings may also be removed, and viewed with a -higher power than when on the leaf, being so transparent as to require -no balsam or other preservative. - -There are few more interesting objects than the _raphides_ or -_plant-crystals_. These are far from being rare, but in some plants -they are very minute, and consequently require care in the mounting, -as well as a high magnifying power to render them visible; in others -they are so large that about twenty-five of them placed point to point -would reach one inch. Some of these crystals are long and comparatively -very thin, which suggested the name (_raphis_, a needle); others are -star-like, with long and slender rays; while others again are of a -somewhat similar form, each ray being solid and short. If the stem -of rhubarb, or almost any of the hyacinth tribe, be bruised, so that -the “juice” may flow upon the slide, in all probability some of these -crystals will be found in the fluid. To obtain them clean, they must be -freed from all vegetable matter by maceration. After this they must be -thoroughly washed and mounted “dry.” They are also good _polarizing_ -objects, giving brilliant colours; but when used for this purpose -they must be mounted as described in Chapter III. A few plants which -contain them may be mentioned here. The Cactaceæ are very prolific; the -orchids, geraniums, tulips, and the outer coating of the onion, furnish -the more unusual forms. - -The Fungi are generally looked upon as a very difficult class of -objects to deal with, but amongst them some of the most available may -be found. The forms of many are very beautiful, but are so minute -as to require a high magnifying power to show them. The mould which -forms on many substances is a fungus, and in some cases may be dried -and preserved in its natural state. A friend of mine brought me a -rose-bush completely covered with a white blight. This was found to be -a fungus, which required a high magnifying power to show it. Being a -very interesting object, it was desirable to preserve it, and this was -perfectly effected without injury to the form by simply drying the leaf -in a room usually occupied. Amongst the fungi are many objects well -worth looking for, one of which is the _Diachæa elegans_. This, the -only species, says the “Micrographic Dictionary,” is found in England -upon the living leaves of the lily-of-the-valley, &c. These little -plants grow in masses, reminding one of mould, to a height of a quarter -of an inch, and each “stem” is covered with a sheath, in shape somewhat -like an elongated thimble. When ripe the sheath falls off and reveals -the same shaped column, made up of beautifully fine net-work, with the -spores lying here and there. This dries well, and is a good object for -the middle powers. Amongst the fungi the blights of wheat and of other -articles of food may be included. Many of them may be mounted “dry;” -others, however, cannot be well preserved except in liquids, and will -be referred to in Chapter IV. Amongst the zoophytes and sea-mats, -commonly called “sea-weeds,” may be found many very interesting objects -to be mounted “dry.” When this mode of preservation is used, it is -necessary that all the sea-salt be thoroughly washed from them. As they -are, however, most frequently mounted in balsam or liquid, they will be -more fully noticed in other places. - -The _scales of fishes_ are generally mounted “dry” when used as -ordinary objects; but for polarized light, balsam or liquid must be -used, as noticed in Chapter III. The variety and beauty of these are -quite surprising to the novice. It is also very interesting to procure -the skin of the fish when possible, and mount it on a separate slide to -show how the scales are arranged. The sole is one of the most unusual -forms, the projecting end of each scale being covered with spines, -which radiate from a common centre, while those at the extremity are -carried out somewhat resembling the rays of a star. One of the skates -has a spine projecting from the centre of each scale, which is a very -curious opaque object, especially when the skin is mounted in the -manner described. The perch, roach, minnow, and others of the common -fishes give the student good objects for his cabinet, and may be -procured without difficulty. - -Insects which are very transparent, or have the “metallic lustre” -with which any medium would interfere, are mounted “dry.” The -diamond-beetle, before mentioned, is a splendid example of this; -the back is generally used, but the legs, showing the curious feet, -are very interesting objects. Indeed, amongst the legs and feet of -insects there is a wide field of interest. When they are of a “horny” -nature, it is best to dry them in any form preferred, but to use no -pressure; when, however, they are wanted flat, so as to show the feet, -&c., extended, they must be dried with a gentle pressure betwixt -blotting-paper if possible. But this will be treated more fully in -Chapter III. - -The _eyes of insects_ are sometimes allowed to dry in their natural -shape, and mounted as opaque objects; but generally they are used as -transparencies in balsam or liquid, so the description of the treatment -which they require will be deferred to Chapter III. - -Hairs, when not too dark, are sometimes transparent enough when mounted -dry, but are usually mounted in balsam. These also will be more fully -noticed in another place. - -These are a few of the objects which are often mounted dry, but some -of them should be shown in balsam or liquid also, and there is much -difference of opinion as to the best way of preserving others. This, -however, is explained by the transparency which the balsam gives -interfering with one property of the object and yet developing another -which would have remained invisible if preserved dry. The only method -of overcoming this difficulty is to keep the object mounted in both -ways, which is comparatively little trouble. - -I may here mention that many prefer the lieberkuhn for the illumination -of opaque objects; and a good background is gained by putting upon the -under side of the slide, immediately beneath the object, a spot of -black varnish, which does not interfere materially with the light. - - - - -CHAPTER III. - -MOUNTING IN CANADA BALSAM. - - -The nature and use of this substance has been before spoken of, so the -method of working with it may be at once described. - -Perfect dryness of the objects is, if possible, more necessary in this -mode of mounting than any other, as dampness remaining in the object -will assuredly cause a cloudiness to make its appearance in a short -time after it is fixed. Where pressure does not injure the specimens, -they are most successfully treated when first dried betwixt the leaves -of a book, or in any other way which may prove most convenient, as -noticed in Chapter II. - -Before describing the methods of proceeding with any particular -objects, general rules may be given which should be observed in order -to succeed in this branch of mounting. - -As the object is to be thoroughly immersed in the balsam, it is evident -that when it has once been covered, so it must remain, unless we again -free it by a process hereafter mentioned, which is very troublesome; -and on this account there must be nothing whatever in the balsam except -the object. The inexperienced may think this an unnecessary caution; -but the greatest difficulty he will meet with is to get rid of minute -bubbles of air, perhaps invisible to the naked eye, which appear -like small globules when under the microscope, and render the slide -unsightly, or even worthless. Ten objects out of eleven contain air, or -at least are full of minute holes which are necessarily filled with it; -so that if they should be immersed in any liquid of thick consistency, -these cells of air would be imprisoned, and become _bubbles_. The air, -then, must be got rid of, and this is usually accomplished by soaking -for some time in turpentine, the period required differing according -to the nature of the object. In some cases, the turpentine acts upon -the colour, or even removes it altogether, so that it must be watched -carefully. Often, however, this is an advantage, as where the structure -alone is wanted, the removal of the colouring matter renders it more -transparent. There are objects, however, which retain the air with such -tenacity that soaking alone will not remove it. If these will bear heat -without being injured, they _may_ be boiled in turpentine, or even in -balsam, when the air will be partly or totally expelled. But where -heat is objectionable, they must be immersed in the turpentine, and so -submitted to the action of the air-pump. Even with this aid, sometimes -days are required to accomplish it perfectly, during which time the air -should be exhausted at intervals of five or six hours, if convenient, -and the objects turned over now and then. - -Sometimes the objects are so minute that it is impossible to submit -them to any soaking, and in this case they must be laid upon the slide -at once, and the turpentine applied to them there. But it must not be -forgotten that there are some few which are much better mounted in such -a way that the balsam may thoroughly surround, and yet not _penetrate_, -the substance more than necessary. Sections of teeth are amongst these, -which will be noticed in another place, and some insects (see Dr. -Carpenter) when required to show the “ramifications of the tracheæ.” - -Having freed the object, then, from these two enemies--dampness and -air--we must proceed to mount it. - -The slide must first be cleaned; then on the centre a quantity of -balsam must be placed with a bluntly-pointed glass rod, according to -the size of the object about to be mounted. To this a slight heat must -be applied, which will cause any bubbles to rise from the surface -of the slide, so that they may be readily removed with a needle. -The object should be freed from all air by steeping in turpentine, -as before described, and then from superfluous liquid by a short -drainage, and carefully laid _upon_, or where it is practicable thrust -_into_, the balsam, prepared on the slide as above. In the former -case, or where the balsam has not totally covered the object, a small -quantity must be taken, warmed, and dropped upon it, and any bubbles -removed by the needle as before. To cover this, the thin glass must be -warmed, and beginning at one side, allowed to fall upon the balsam, -driving a small “wave” before it, and thus expelling any bubbles which -may remain. This is quite as safely performed (if not more so) by -making a solution of balsam in turpentine of the consistency of thick -varnish. The thin glass cover may be slightly coated with this, and -will then be much less liable to imprison any air, which frequently -happens when the cover is dry. Bubbles, however, will sometimes -make their appearance in spite of all care; but when the object is -comparatively strong, they may be removed by keeping the slide rather -warm, and _working_ the cover a little, so as to press them to one -side, when they should be immediately removed with a needle point, -otherwise they are again drawn under. - -Where the slide requires keeping warm for any length of time, a -_hot-water bath_ is sometimes made use of, which is simply a flat -tin, or other metal case, with a mouth at the side, that when the hot -water is introduced it may be closed up, and so retain its warmth for -a long time. In working, the slide is laid upon it, and so admits of -longer operations, when required, without growing cold. Sometimes -a spirit-lamp is placed under it to keep up an equal heat through -excessively long processes. Where the time required, however, is but -short, a thick brass plate is sometimes used (see Chapter I.), which is -heated to any degree that is required, and the slide placed upon it. - -Some objects, which are so thin that they are usually _floated_ upon -the slide, as before stated, require no steeping in turpentine or other -liquid. These are best mounted by covering with a little _diluted_ -balsam, and after this has had time to penetrate the substance, -ordinary balsam is laid upon it, and the slide finished in the usual -manner. - -I have stated that the balsam is usually applied to the slide and -objects with a “bluntly-pointed glass rod;” but for the purpose of -drawing the balsam from the bottle, and conveying it to the desired -place, Dr. Carpenter uses a glass syringe with a _free_ opening. These -are his instructions:--“This (the syringe) is most readily filled with -balsam, in the first instance, by drawing out the piston, and pouring -in balsam previously rendered more liquid by gentle warmth; and nothing -else is required to enable the operator at any time to expel precisely -the amount of balsam he may require, than to warm the point of the -syringe, if the balsam should have hardened in it, and to apply a very -gentle heat to the syringe generally, if the piston should not then be -readily pressed down. When a number of balsam objects are being mounted -at one time, the advantage of this plan in regard to facility and -cleanliness (no superfluous balsam being deposited on the slide) will -make itself sensibly felt.” - -When the “mounting” is thus far accomplished, the outer “wall” of -balsam may be roughly removed after a few hours have elapsed; but -great care is necessary lest the cover be moved or interfered with in -any way. In this state it may be left for the final cleansing until -the balsam becomes hard, which takes place sooner or later, according -to the degree of warmth it has been subjected to. A mantel-piece, or -some place about equal to it in temperature, is the best suited to -this purpose; and when the requisite hardness is attained, it may be -proceeded with as follows:--With a pointed knife the balsam must be -scraped away, taking care that the thin glass be not cracked by the -point getting _under_ it. If used carefully, the knife will render the -slide almost clean; but any minute portions which still adhere to the -glass must be rubbed with linen dipped in turpentine or spirit. If the -balsam is not very hard, these small fragments are readily removed by -folding a piece of paper tightly in a triangular form with many folds, -and damping the point with which the glass is rubbed. As the paper -becomes worn with the friction, the balsam will be carried off with it. -In some cases I have found this simple expedient very useful. - -Sometimes the object to be mounted is of such a thickness as to -require a cell. For this purpose glass rings are used (as described in -Chapter IV.), and filled with balsam. The best mode of doing this is -thus described by Mr. T. S. Ralph in the _Microscopic Journal_:--“The -question was asked me when I was in England, if I knew how to fill a -cell with Canada balsam and leave behind no air-bubbles? I replied in -the negative; but now I can state how to accomplish this. Fill the cell -with clear spirit of turpentine, place the specimen in it, have ready -some balsam just fluid enough to flow out of the bottle when warmed by -the hand; pour this on the object at one end, and, gradually inclining -the slide, allow the spirit of turpentine to flow out on the opposite -side of the cell till it is full of balsam; then take up the cover, and -carefully place upon it a small streak of Canada balsam from one end -to the other. This, if laid on the cell with one edge first, and then -gradually lowered until it lies flat, will drive all the air before -it, and prevent any bubbles from being included in the cell. It can -be easily put on so neatly as to require no cleaning when dry. If the -cover is pressed down too rapidly, the balsam will flow over it, and -require to be cleaned off when hardened, for it cannot be done safely -while fluid at the edges.” - -Sometimes with every care bubbles are enclosed in the balsam, injuring -objects which are perhaps rare and valuable. The whole slide must then -be immersed in turpentine until the cover is removed by the solution of -the balsam; and the object must be cleansed by a similar steeping. It -may then be remounted as if new in the manner before described. - -The balsam and chloroform described in Chapter I. is thus used; and -where the object is thin, the mounting is very easily accomplished. -When the object is laid upon the slide with a piece of glass upon it, -and the balsam and chloroform placed at the edge of the cover, the -mixture will gradually flow into the space betwixt the glasses until -the object is surrounded by it, and the unoccupied portion filled. The -chloroform will evaporate so quickly that the outer edge will become -hard in a very short time, when it may be cleaned in the ordinary way. -Sometimes the balsam is dissolved in the chloroform without being first -hardened; but this is only to render it more fluid, and so give the -operator less chance of leaving bubbles in the finished slide, as the -thicker the medium is, the more difficult is it to get rid of these -intruders. - -It has been before mentioned that some have objected to chloroform -and balsam, believing that it became _clouded_ after a certain time. -Perhaps this may be accounted for in part by the fact that almost all -objects have a certain amount of dampness in them. Others are kept in -some preservative liquid until the time of mounting, and these liquids -generally contain certain salts (Chapter IV.). If this dampness, as -well as all traces of these salts, however small, are not totally -removed--the former by drying, the latter by repeated washings--the -addition of chloroform will render the balsam much more liable to the -cloudiness than when balsam alone was used, as before mentioned. - -This mode of employing the balsam, however, will not be always -applicable, as _chloroform_ acts upon some substances which balsam -_alone_ does not. Some salts are even soluble in it, the crystals -disappearing after a few days or weeks, whereas in the balsam alone -they are quite permanent. Experience is the only guide in some cases, -whilst in others a little forethought will be all that is required. - -The particular methods used for certain objects may be now entered -upon. Many of the Diatomaceæ and fossil Infusoria, as they are -sometimes termed, are mounted dry, and cleaned in the way described in -Chapter II. Others are almost always placed in balsam, except where -they are intended to be used with the lieberkuhn and dark background, -by which means some of them are rendered exquisitely beautiful. The -usual way of mounting them in balsam is as follows:--Take a drop of -the water containing them, place it upon the slide, and evaporate over -the lamp, whilst with a needle they may be dispersed over any space -desired. When they are thoroughly dry, drop a little balsam on one -side, and exclude the bubbles. The slide may then be warmed to such -a degree that the balsam, by lifting the glass at one end, will be -carried over the specimens, which may then be covered with thin glass, -made warm as before described. Where the objects are quite dry, and -loose upon the glass, it requires great care in placing the cover upon -them, otherwise they are forced to one edge, or altogether from under -it, in the wave of the balsam. For this reason, Professor Williamson -adds a few drops of gum-water to the last washing, which causes them to -adhere sufficiently to the glass to prevent any such mishap. - -Mr. T. G. Rylands’ method differs in some degree from the above, and -is, to use his own words, as follows:--Thick balsam is preferable, -and the burnt covers (see Chapter II.) to be mounted are laid in a -convenient position with the diatoms upwards. The slides required -having been carefully cleaned and marked on the under side with a ring -of ink, by the aid of a turntable about half an inch in diameter to -point out the centre, a drop of benzole is applied by a large pin to -the diatoms on the cover, so as to exclude the air from the valves -and frustules. The slide is then held over the lamp, and when warm, -a sufficiently large drop of balsam is put upon it, and heated until -it begins to steam. If small bubbles appear, a puff of breath removes -them. The slide being held slightly inclined from the operator, and the -drop of balsam becoming convex at its lower edge, the cover is brought -in contact with it at that point, gradually laid down, pressed with the -forceps, and brought to its central position. When cool the superfluous -balsam (if any) is removed with a heated knife-blade, the slide cleaned -with a little turpentine, and finished by washing in a hand-basin with -soap and water. In this process there is no delay if the balsam be -sufficiently thick, as the slide may be cleaned off almost before it is -cold. - -It is now well known that from common chalk it is an easy matter to -obtain interesting specimens of Foraminifera. Scrape a small quantity -of chalk from the mass and shake it in water; leave this a few minutes, -pour the water away and add a fresh quantity, shake up as before, and -repeat two or three times. Take a little of the residue, and spread it -upon the slide, and when quite dry add a little turpentine. When viewed -with a power of two hundred and fifty diameters this will generally -show the organisms very well. If it is desired to preserve the slides, -they may be then mounted in Canada balsam. Mr. Guyon, in “Recreative -Science,” observes that the accumulation of the powder, by the action -of the rain or exposure to the atmospheric action, at the foot or any -projection of the chalk cliffs, will afford us better specimens than -that which is “scraped,” as the organisms are less broken in the former. - -When the Foraminifera are of a larger size, though transparent enough -to be mounted in balsam, the air must be first expelled from the -interior, otherwise the objects will be altogether unsatisfactory. To -accomplish this they must be immersed in turpentine and submitted to -the action of the air-pump. So difficult is it to get rid of this enemy -that it is often necessary to employ three or four exhaustions, leaving -them for some time under each. When all air has given place to the -turpentine, they must be mounted in the ordinary way. - -Of all objects which are commonly met with, few are such general -favourites as the POLYCYSTINÆ, and deservedly so. Their forms are -most beautiful, and often peculiar--stars varying in design, others -closely resembling crowns; the _Astromma Aristotelis_ like a cross, -and many whose shapes no words could describe. The greater part, -perhaps, of those which are usually sold, is from the rocky parts of -Bermuda; but they are also found in Sicily, some parts of Africa and -America. They are usually mounted in balsam, but are equally beautiful -mounted “dry” and used with the lieberkuhn. They require as much care -in cleaning as the Diatomaceæ, but the process is a different one. -Sometimes this is effected by simply washing until they are freed from -all extraneous matter, but this is seldom as effectual as it should be. -In the _Microscopic Journal_ Mr. Furlong gives the following method of -treatment as the best he knew:-- - -Procure-- - - A large glass vessel with 3 or 4 quarts of water. - - New tin saucepan holding 1 pint. - - 2 thin precipitating glasses holding 10 oz. each. - -Take 3 oz. of dry “Barbadoes earth” (lumps are best), and break into -rather small fragments. Put 3 or 4 oz. of common washing soda into the -tin and half fill it with water. Boil strongly, and having thrown in -the earth, boil it for half an hour. Pour nine-tenths of this into the -large glass vessel, and gently crush the remaining lumps with a soft -bristle brush. Add soda and water as before, and boil again; then pour -off the liquid into the large vessel, and repeat until nothing of value -remains. Stir the large vessel with an ivory spatula, let it stand for -three minutes, and pour gently off nine-tenths of the contents, when -the shells will be left, partially freed only, like sand. - -2ND PROCESS.--Put common washing soda and water into the tin as before, -and having placed the shells therein, boil for an hour. Transfer to the -large vessel as before, and after allowing it to stand for one minute -pour off. Each washing brings off a kind of “flock,” which seems to be -skins. - -3RD PROCESS.--Put the shells in precipitating glass and drain off the -water until not more than ½ oz. remains. Add half a teaspoonful of -bicarbonate of soda, dissolve, and then pour in gently 1 oz. of strong -sulphuric acid. This liberates the “flock,” &c., and leaves the shells -beautifully transparent. Wash well now with water to get rid of all -salts and other soluble matter. - -Some of the large shells are destroyed by this method, but none that -are fit for microscopic use. An oblique light shows these objects best. - -These are sometimes treated in the manner described in Chapter II. -where the diatoms are spoken of, but many forms are liable to be -injured by this severe process. - -It has been before stated that some of the zoophytes may be mounted -dry, and others examined as opaque or transparent objects according to -their substance. They are very interesting when examined in the trough -whilst living, but to preserve many of them for future examination they -must be mounted in some preservative medium. Sometimes this may be one -of the liquids mentioned in Chapter IV., but if possible they should -be kept in balsam, as there is less danger of injury by accident to -this kind of slide. This method of mounting presents some difficulties, -but I think that all agree as to the trustworthiness of Dr. Golding -Bird’s information on the subject, which appeared in the _Microscopic -Journal_. Of this, space forbids me to give more than a condensed -account, but I hope to omit nothing of moment to the reader for whom -these pages are written. - -After stating that there are few who are not familiar with these -exquisite forms, and have not regretted the great loss of beauty -they sustain in dying, he informs us that from their so obstinately -retaining air in the cells and tubes when dried, it is hardly -practicable to get rid of it; and they also shrivel up very seriously -in the process of drying. The following plan, however, he has found -almost faultless in their preparation. - -To preserve them with extended tentacles, they should be plunged in -cold fresh water, which kills them so quickly that these are not often -retracted. The specimens should be preserved in spirit until there is -leisure to prepare them; if, however, they have been _dried_, they -should be soaked in cold water for a day or two before being submitted -to the following processes:-- - -1. After selecting perfect specimens of suitable size, immerse them -in water heated to about 120° and place them under the receiver of an -air-pump. Slowly exhaust the air, when bubbles will rise and the water -appear to be in a state of active ebullition. After a few minutes -re-admit the air and again exhaust, repeating the process three or four -times. This will displace the air from most, if not all, of the class. - -2. Remove the specimens and allow them to drain upon blotting-paper -for a few seconds; then place them in an earthen vessel fitted with a -cover, and previously heated to about 200°. This heat may be easily -got by placing the vessel for a short time in boiling water, wiping -it immediately before use with a thick cloth. The specimens are then -dropped into this, covered with the lid, and immediately placed under -the receiver of the air-pump, and the air rapidly exhausted. By this -means they are dried completely, and so quickly that the cells have no -time to wrinkle. - -3. In an hour or two remove them from the air-pump and drop them into -a vessel of perfectly transparent camphine. This may be quite cold -when the horny, tubular polypidoms, as those of the Sertulariæ, are -used; but should be previously heated to 100° when the calcareous, -cellular Polyzoa are the objects to be preserved. The vessel should be -covered with a watch-glass and placed under the receiver, the air being -exhausted and re-admitted two or three times. - -4. The slide which is to receive the specimen should be well cleaned -and warmed so as to allow the balsam to flow freely over it. This -must be applied in good quantity, and air-bubbles removed with the -needle-point. Take the polypidom from the camphine, drain it a little, -and with the forceps immerse it fully in the balsam. The glass to be -laid upon it should be warmed and its surface covered with a thin -layer of balsam, and then lowered gradually upon it, when no bubbles -should be imprisoned. A narrow piece of card-board at each end of the -object for the cover to rest upon, prevents any danger of crushing the -specimen. - -This mode of mounting polypidoms, &c., seems to give almost the -complete beauty of the fresh specimens. They are very beautiful objects -when viewed with common light, but much more so when the polarizer is -used (in the manner described a little farther on). - -To the above instructions there can be little to add; but I may here -mention that some young students may not be possessed of the air-pump, -and on this account put aside all search for those specimens which need -little looking for at the seaside. Many of these, however, though they -lose some beauty by the ordinary mode of drying, will by steeping for -some time in turpentine not only be freed from the air-bubbles, but -suffer so little contraction that they are a worthy addition to the -cabinet. - -Another class of objects is the _spicula_ met with in sponges, &c. -These are often glass-like in appearance and of various shapes; many -are found resembling needles (whence their name); some from the synapta -are anchor-like, whilst others are star-like and of complex and almost -indescribable combinations. As some of these are composed of silex and -are consequently not injured by the use of nitric acid, the animal -substance may be got rid of by boiling them in it. Those, however, -which are calcareous must be treated with a strong solution of potash -instead; but whichever way is used, of course they must afterwards be -freed from every trace of residue by careful washing. - -These spicules may be often found amongst the sand which generally -accumulates at the bottom of the jars in which sponges are kept by -those who deal in them, and must be picked out with a camel-hair -pencil. The specimens obtained by this means will seldom if ever -require any cleaning process, as they are quite free from animal -matter, &c. - -In the former chapter was noticed those insects or parts of them which -are usually mounted dry. When they are large and too opaque to admit of -the dry treatment, they must be preserved in Canada balsam or fluid. -The first of these may now be considered. - -It may be here mentioned, that with these objects much heat must not be -employed, as it would in some instances give rise to a cloudiness, and -almost invariably injure them. - -In killing the insect it is necessary not to rub or break any part of -it. This may be performed by placing it in a small box half filled with -fragments of fresh laurel leaves, by immersion in turpentine or strong -spirit, as also in solutions of various poisonous salts. After which -it may be preserved for sometime in turpentine or other preservative -liquid (Chapter IV.) until required. As an assistance to the student, -I believe that I can do no better than give him the plan pursued by my -friend Mr. Hepworth, whose specimens are in every way satisfactory; -but when his method is used, the insects must not have been placed in -turpentine for preservation:-- - -“After destroying the insects in chloroform or sulphuric ether -(methylated being cheaper), wash them thoroughly in a wide-necked -bottle, half-filled, with two or three waters; the delicate ones -requiring great care. Then immerse them in liquid potash (or Brandish’s -solution, which is stronger than the usual preparation), and let them -remain a longer or shorter time according to their texture. When ready -to remove, put one by one into a small saucer of clear water, and with -a camel-hair pencil in each hand press them flat to the bottom, holding -the head and thorax with the left-hand brush, and apply pressure with -the other from above, downwards, giving the brush a rolling motion, -which generally expels the contents of the abdomen from the thorax. -A minute roller of pith or cork might be used instead of the brush. -In larger objects, use the end of the finger to flatten them. Large -objects require more frequent washing, as it is desirable to remove the -potash thoroughly, or crystals are apt to form after mounting. Having -placed them on the slides with thin glass covers, tied down with -thread,[C] dry and immerse them in rectified spirits of turpentine; -place the vessel under the receiver of an air-pump, and keep it -exhausted until the turpentine has taken the place of the air-bubbles: -they are then ready for the application of the balsam. Larger objects -may often with advantage be transferred to a clean slide, as during the -drying there is considerable contraction, and an outline often remains -beyond the margin showing this. When closely corked they may remain in -the spirits two or three months. As you take them from the bottle, wipe -as much turpentine off as possible before removing the thread, and when -untied carefully wipe again, placing the finger on one end of the cover -whilst you wipe the other, and vice versâ. By this means you remove -as much turpentine from under the cover as is necessary; then drop -the balsam, thinned with chloroform (see Chapter I.), upon the slide, -letting the fluid touch the cover, when it will be taken in between the -surfaces by capillary attraction; and after pressing the cover down it -may be left to dry, or you may hold the slide over a spirit-lamp for -a few seconds before pressing down the cover. If heat is not applied, -they are much longer in drying but are more transparent. If made too -hot the boiling disarranges the objects, and if carried too far will -leave only the resin of the balsam, rendering it so brittle that the -cover is apt to fly off by a fall or any jar producing sufficient -percussion. Never lift the cover up, if possible, during the operation, -as there is danger of admitting air. A few bubbles may appear -immediately after mounting, but generally subside after a few hours, -being only the chloroform or turpentine in a state of vapour, which -becomes condensed.” - - [C] This applies to the more delicate ones, which will not bear - transferring after being once spread out and dried. - -This method of preparing and mounting insects I can strongly recommend -as giving first-rate results; but where the specimens are small they -seldom need the soaking in caustic potash which larger ones must have. -It is only necessary to leave them awhile in turpentine, especially -when they have been first dried with gentle pressure between two -glasses, and then mount with balsam in the ordinary way. - -Amongst the insect tribes there is abundant employment, especially -for the lower powers of the microscope. But if the deeper wonders and -beauties of the animal economy are to be sought out and studied, it is -desirable that the various parts should be set separately, in order -that they may receive a more undivided attention, as well as to render -them capable of being dealt with under the higher powers. We will, -therefore, briefly consider the treatment which the different portions -require. - -The eyes of the butterflies, and indeed of almost all insects, afford -materials for a study which is complete in itself. When examined with -a tolerably high power, instead of finding each eye with an unbroken -spherical surface, it is seen that many are composed of thousands of -hexagonal divisions, each being the outer surface of a separate portion -termed the _ocellus_. In others these divisions are square; but in -all there is a layer of dark pigment surrounding their lower parts. -The ocelli may be partly removed from the eye, which will show how -their tapering forms are arranged. But here we have to consider how to -place them in balsam for preservation. The eye being removed from the -insect, and the dark pigment removed by the use of a camel-hair pencil, -must be allowed to remain in turpentine at least for some days. The -turpentine should then be renewed and the eye well washed in it just -before it is to be mounted. It may then be set in balsam in the same -way as any other object;--but here a difficulty is met with. The eye -being spherical upon the surface required, must necessarily be “folded” -or broken in attempting to flatten it. This difficulty may be often -overcome by cutting a number of slits round the edges; but some object -to this mode of treatment, and where it is practicable it is much more -satisfactory to mount one in the natural rounded form and another -flat. Instead, however, of mounting the organ _whole_, four or five -slides may be procured from each of the larger ones, as those of the -dragon-fly, &c. - -The _antennæ_ also are often mounted on separate slides, as being -better suited for higher powers and more minute examination than when -connected with the insect. These two projecting organs, issuing from -the head, are jointed, and moveable at will. They differ very much in -form amongst the various species, and are well worth the attention of -the microscopist. They are usually mounted with the head attached, and -perhaps they are more interesting when thus seen. Some few are very -opaque, to prepare which the following method has been advised:-- - -Bleach the antennæ by soaking in the following solution for a day or -two:-- - - Hydrochloric acid, 10 drops. - Chlorate of potash, ½ drachm. - Water, 1 oz. - -This will render them transparent. Wash well, dry, and mount in Canada -balsam. Instead of the above, a weak solution of chloride of lime may -be used, by which means the nerves will be well shown. Many, however, -are rendered transparent enough by simply soaking in turpentine for -a longer or shorter time. Where the antennæ, however, are “plumose,” -or feather-like, extreme care is required in mounting, though the -difficulty is not so great as some seem to think. If they are first -dried with gentle pressure, and then subjected to the action of the -air-pump in a small quantity of turpentine until the air is thoroughly -expelled, they can be easily finished upon the slide, especially when -balsam and chloroform are used. - -Insects supply us with another series of beautiful objects, viz., -the _feet_.[D] These are sometimes simply dried and mounted without -any medium, as before mentioned; but most of them are rendered much -more fit for examination by using balsam in their preservation, as it -greatly increases their transparency. The smaller kinds may be dried -with gentle pressure betwixt blotting-paper, and then immersed for -some days in turpentine, without requiring the treatment with liquor -potassæ. This immersion will render them beautifully transparent, when -they may be mounted in balsam in the usual manner. - - [D] See Mr. Hepworth’s interesting articles on the fly’s - foot in the second and third volumes of the _Microscopic - Journal_. - -It is, however, sometimes found difficult to fix the feet when -_expanded_, in which state the interest of the object is greatly -increased. Mr. Ralph recommends the following mode:--“First wash -the feet, while the insect is yet alive, with spirits of wine; then -holding it by a pair of forceps close to the edge of a clean piece of -glass, the insect will lay hold of the upper surface by its foot, then -suddenly drop another small piece of glass over it, so as to retain -the foot expanded, and cut it off with a pair of scissors, tie up and -soak to get rid of air.” Mr. Hepworth says that he never found any -difficulty in expanding the foot on a drop of water or well-wetted -slide, and laying a thin glass cover over it, tying with thread, -drying, and immersing in turpentine. - -The mouth, also, with its organs, is an interesting object in -many insects. That of the common fly is often made use of, and is -comparatively easy to prepare. By pressing the head, the tongue (as it -is commonly termed) will be forced to protrude, when it must be secured -by the same means as the foot, and may be subjected to the soaking -in turpentine, and mounted as usual. The honey-bee is, however, very -different in formation, and is well worth another slide; indeed, even -in insects of the same class, the differences are many and interesting. - -Another worthy object of study is the _respiration_ of insects, which -is effected by tracheæ or hollow tubes, which generally run through the -body in one or more large trunks, branching out on every side. These -terminate at the surface in openings, which are termed _spiracles_, or -breathing organs. The _tracheæ_ often present the appearance of tubes -constructed by a twisted thread, somewhat resembling the spiral fibres -of some plants. These are very beautiful objects, and are generally -mounted in balsam, for which reason they are mentioned here; but as -they evidently belong to the “dissecting portion,” they will be fully -treated of in another place. - -Amongst the parasitic insects a great variety of microscopic subjects -will be found. As these are usually small, they may be killed by -immersion in spirits of turpentine; and if at all opaque, may be -allowed to remain in the liquid until transparent enough, and then -mounted in Canada balsam. - -The acarida, or _mites_ and _ticks_, are well known; none, perhaps, -better than those which are so often found upon cheese. Flour, -sugar, figs, and other eatables, are much infested by them; whilst -the diseases called the _itch_ in man, and the _mange_ in animals, -are produced by creatures belonging to this tribe. These animals -are sometimes mounted by simply steeping them in turpentine, and -proceeding as with other insects. The “Micrographic Dictionary” gives -the following directions as to mounting _parts_ of these:--“The parts -of the mouth and the legs, upon which the characters are usually -founded, may be best made out by crushing the animals upon a slide with -a thin glass cover, and washing away the exuding substance with water; -sometimes hot solution of potash is requisite, with the subsequent -addition of acetic acid, and further washing. When afterwards dried -and immersed in Canada balsam, the various parts become beautifully -distinct, and may be permanently preserved.” - -Feathers of different kinds of birds are usually mounted in balsam -when required to show much of the structure. This is particularly -interesting when the feathers are small, as they then show the -inner substance, or _pith_, as it may be termed, with the cells, -&c. The “pinnæ,” or soft branches of the feathers, will be found -of various constructions; some possessing hooks along one side, -whereby they fasten themselves to their neighbours; others branching -out, with straight points somewhat resembling the hairs from certain -caterpillars. But, of course, when the metallic-looking gorgeous -colours are all that is required to be shown, and reflected light used -(as with the feathers of the hummingbird, peacock, &c.), it is much -better that they should be mounted dry, as in Chapter II. - -The _seeds_ and _pollen_ of plants are most frequently mounted dry, -as mentioned in Chapter II.; but the more transparent of the former, -and the darker kinds of the latter, are perhaps better seen in Canada -balsam. There is nothing particular to be observed in the manipulation, -except that the glass cover must be applied lightly, otherwise the -grains may be crushed. There are some objects which cannot be shown -in a perfect manner when mounted _dry_, but when immersed in balsam -become so very transparent that they are almost useless. To avoid this, -it has been recommended to stain the objects any colour that may be -convenient, and afterwards mount in balsam in the ordinary manner. - -Most objects intended for the polariscope may be mounted in Canada -balsam; but there are some exceptions to this. Many of the salts are -soluble in this medium, or their forms so injured by it, that glycerine -or oil has to be used (see Chapter IV.); others must be left in the dry -form, as before mentioned; and some few it is impossible to preserve -unchanged for any length of time. _Crystals_, however, are amongst the -most beautiful and interesting subjects for polarisation; and it is -very probable that, by the aid of the polariscope, new and valuable -facts are yet to be made known. For one who finds pleasure in form -and colour, there is a field here which will only open wider upon him -as he advances; and instead of being in anywise a merely mechanical -occupation, it requires deep and careful study. The little here said on -the subject will show this in some degree. - -With almost every salt the method of _crystallization_ must be modified -to obtain the best forms; I may even go further than this, and say that -it is possible to change these forms to such a degree that the eye -can perceive no relationship to exist betwixt them. If a solution of -sulphate of iron is made, a small quantity spread evenly upon a slide, -and then suffered to dry whilst in a flat position, the crystals often -resemble the fronds of the common fern in shape. But if, whilst the -liquid is evaporating, it is kept in motion by stirring with a thin -glass rod, the crystals form separately, each rhombic prism having its -angles well defined, and giving beautiful colours with the polarized -light. Again, pyro-gallic acid, when allowed to flow evenly over the -slide in a saturated solution, covers the surface in long “needles,” -which are richly coloured by polarized light; but if any small portion -of dust or other matter should form a nucleus around which these -“needles” may gather, the beauty is wonderfully increased. A form very -closely resembling the “eye” of the peacock’s tail, both in form and -colour, is then produced, which to one uninitiated in crystallography -bears very little resemblance to the original crystal. From these -simple facts it will be clearly seen that in this, as in every other -department, study and experience are needful to give the best results. - -To obtain anything like uniformity in the formation of crystals upon -the glass slide, every trace of grease must be removed by cleaning with -liquor potassæ or ammonia immediately before using, care also being -taken that none of the agent is left upon the slide, otherwise it may -interrupt and change their relative position, and even their form. - -Amongst those which are generally esteemed, the most beautiful are the -crystals of oxalurate of ammonia. The preparation of this salt from -uric acid and ammonia is a rather difficult process, and will not on -that account be described here; but when possessed, a small quantity -of a strong solution in water must be made, and a little placed -on the slide, and evaporated slowly. Part of the salt will then be -deposited in circles with the needle-like crystals extending from -common centres. They should then be mounted in pure Canada balsam; -and, when the best colours are wanted, used with the selenite plate. -Of this class of crystal salicine is a universal favourite, and can be -easily procured of most chemists. The crystals may be produced in two -ways:--A small portion of the salt must be placed upon the slide, and a -strong heat applied underneath until fusion ensues; the matter should -then be evenly and thinly spread over the surface. In a short time -the crystals will form, and are generally larger than those procured -by the following process; but the uncertainty is increased a little -when fusion is used, which, however, is desirable with many salts. -Secondly, make a saturated solution of salicine, which in cold water -is effected by adding one part of the salt to eighteen parts of water. -Lay a little upon the slide, and allow it to evaporate spontaneously, -or with the aid of gentle heat. The crystals are generally uniform, and -with ordinary powers quite large enough to afford a beautiful object. -The circular shape and gorgeous colours of this crystal have made it so -great a favourite that there are few cabinets without it. - -Many new forms may be procured by uniting two totally different salts -in solution in certain proportions. This is a field affording new -facts and beauties; but requires some chemical knowledge and much -perseverance to obtain very valuable results. One of the most beautiful -I have met with has been composed of sulphate of copper and sulphate of -magnesia. The flower-like forms and uniformity of crystallization when -successful make it well worth a few failures at first; and as I became -acquainted with some new facts in my frequent trials, I will give the -preparation of the double salt from the beginning. - -Make a saturated solution of the two sulphates, combined in the -proportion of three parts copper to one part magnesia, and then add -to the solution one-tenth of pure water. Dust or other impurities -should be guarded against, and the slide made free from all trace -of grease by cleaning immediately before use with liquor potassæ or -ammonia. A drop of the solution should then be placed upon the slide, -and by a thin glass rod spread evenly upon the surface. Heat this -whilst in a horizontal position until the salt remains as a viscous -transparent substance, which will not be effected until it is raised -to a high degree. The slide may now be allowed to cool, and when this -is accomplished, the flower-like crystals will be perceived forming -here and there upon the plate. When these are at any stage in which it -is wished to preserve them, a few seconds’ exposure to the fire, as -warm as the hand can comfortably bear, will stop the expansion, when -the portion which we wish to mount should be cut off from the mass of -salt by simply scratching the film around, and pure Canada balsam with -the thin glass used. Breathing upon the film, or allowing the slide to -become cold and attract the moisture from the atmosphere, will cause -the crystallization to extend, and sometimes greatly rob the effect; so -it is necessary to mount quickly when the desired forms are obtained. -As the crystals are very uncertain as to the place of their formation, -I may here mention that they may be got in _any_ part of the slide -by piercing the film with a needle-point; but in some degree this -necessarily interferes with the centre. As the cause of this has no -need to be entered into here, and has been elsewhere discussed, I shall -only give the above directions, and say that there is a great field in -this branch of study which the microscope alone has opened. - -It would be useless to enter into particulars respecting the various -salts and treatment they require, as a great difference is effected -even by the strength of the solution. There are some crystals, also, -which are called forth in insulated portions, showing no formation -upon the ground; but even when mounted in any preserving fluid, and -unchanged for a year, a new action seems to arise, and a groundwork -is produced which bears little resemblance to the original crystal. -Sometimes this new formation adds to the beauty of the slide; in other -cases the reverse is the result, the slide being rendered almost -worthless. This action, I believe, frequently arises from some liquid -being contained in the balsam or other mounting medium used; and this -is rendered the more probable by the crystallization being called -forth in an hour after the balsam diluted with chloroform is employed, -whereas no change would have taken place for months (if at all) had -pure balsam been used. - -Sections of some of the salts are very interesting objects, but the -method of procuring these and their nature will be described in Chapter -V. - -The scales of various fish have been before mentioned as mounted “dry;” -when, however, they are required for polarising objects they are -generally mounted in balsam, and some few in liquid. The former method -will be considered here. - -The eel affords a beautiful object for this purpose. The scales are -covered by a thin “_skin_,” which may be slightly raised with a knife -and then torn off, in the same manner as the covering of the geranium -and other petals, described in Chapter II. The required portion may -then be removed; or if a piece of skin can be procured as stripped off -in cooking, the scales may be easily taken from the inner surface. They -must then be washed and thoroughly cleaned. After drying, soak for a -day in turpentine, and mount in the ordinary manner with balsam. This -is a good polarising object; but the interest, and I think the beauty, -is increased by procuring a piece of eel’s skin with the scales _in -sitû_, washing and drying under pressure, and mounting in balsam as -before. The arrangement of the scales produces beautiful “waves” of -colour, which are quite soothing to the eye after examining some of the -very gorgeous salts, &c. - -There are many scales of fish which are good subjects for the -polariscope when mounted in balsam; but as they require no particular -treatment, they need no mention by name. - -Among hairs we find some which are beautiful when mounted in balsam -and examined by polarized light. Some, when wanted as common objects, -are always used dry, as before mentioned; but if they are intended to -be shown as _polarizing_ objects, they must be placed in some medium. -The “Micrographic Dictionary” mentions a mode of making an interesting -object by plaiting two series of white horse-hairs at an angle, -mounting in balsam, and using with the polariscope. All hairs, however, -must be steeped in turpentine for a short time before mounting, as they -will thus be rendered cleaner and more transparent. When this is done, -there is no difficulty in mounting them. - -Many of the “tongues” of fresh-water and marine mollusca are deeply -interesting and most beautiful objects when examined by polarized -light. As these are usually mounted in balsam, I mention them in this -place; but as they must be removed from the animals by dissection, -particulars respecting them will not be entered into until we come to -the part in which that operation is described (Chapter V.). - -The manner of preparing and mounting many of the Polyzoa and Zoophytes -has been before described; but any notice of _polarizing_ objects would -be incomplete without some allusion to them. A small piece of the -_Flustra avicularis_, well prepared, is beautiful when examined in this -manner. No selenite is needed, and yet the colours are truly gorgeous. -It is often met with upon shells and zoophytes of a large size, and -will well repay the trouble of searching for. Many of the Sertularidæ -are very beautiful with polarized light, and, indeed, no ramble upon -the seaside need be fruitless in this direction. - -The different _starches_ are quite a study in themselves, and -are peculiarly connected with polarized light. They are found in -the cellular tissue of almost every plant in small white grains -which vary considerably in size; that from the potato averages -one-three-hundredth of an inch in diameter, and that from arrow-root -about one-six-hundredth. To procure starch from any plant, the texture -must first be broken up or ground coarsely; the mass of matter must be -then well washed in gently-flowing water, and, as all starch is totally -insoluble in cold water, the grains are carried off by the current -and deposited where this is stayed. In procuring it from the potato, -as well as many other vegetables, it is but necessary to reduce the -substance to a coarse pulp by the aid of a culinary “grater;” the pulp -should then be well agitated in water, and allowed to rest a short -time, when the starch will be found at the bottom, its lighter colour -rendering it easily distinguishable from the pulp. It should, however, -be washed through two or three waters to render it perfectly clean. - -These grains have no crystalline structure, but present a very peculiar -appearance when examined with polarized light. Each grain shows a dark -cross whose lines meet at the point where it was attached to the plant, -called the _hilum_. Round the grain, also, a series of lines are seen, -as though it were put together in plates. This is more distinctly -visible in some kinds than others. - -As to the mounting of these starches there is little to be said. If the -grains are laid upon the slide, and as small a portion as possible of -the balsam diluted with turpentine, as before mentioned, be applied, -they will cling to the glass and allow the pure balsam to flow readily -over them without being so liable to imprison air-bubbles when the thin -glass is put upon them. - -The raphides, which were fully described in Chapter II., when required -for use with polarized light, must be mounted in balsam, and many are -found which give beautiful colours. They require no peculiar treatment, -but must be washed quite clean before putting up. - -There is one class of objects for the polariscope which differs in -preparation from any we have yet considered, and affords very beautiful -specimens. Some of the plants, including many of the grasses and -the Equisetaceæ (_i. e._ horsetails), contain so large a quantity -of silica, that when the vegetable and other perishable parts are -removed, a skeleton of wonderful perfection remains. This skeleton -must be mounted in balsam, the method of performing which will now be -considered. - -Sometimes the cuticle of the equisetum is removed from the plant, -others dry the stem under pressure, whilst the grasses, of course, -require no preparation. The vegetable should be immersed in strong -nitric acid and boiled for a short time; an effervescence will go on -as the alkalies are being removed, and when this has ceased more acid -should be added. At this point the modes of treatment differ; some -remove the object from the acid and wash, and having dried, burn it -upon thin glass until all appears _white_, when it must be carefully -mounted in balsam. I think, however, it is better to leave it in strong -acid until all the substance, except the required portion, is removed; -but this will take a length of time, varying according to the mass, -&c., of the plant. Of course, when this latter method is used, the -skeleton must be washed from the acid, &c., before being mounted in -balsam. - -These _siliceous cuticles_ are readily found. The _straws_ of most of -the cereals, wheat, oat, &c.; the _husks_, also, of some of these; many -_canes_; the equisetum, as before described; and some of the grasses. -Many of these are everywhere procurable, so that the student can never -want material for a splendid object for the polariscope. - -In Chapter II. the _scales_ (or hairs) which are often found upon the -leaves of plants were mentioned as beautiful objects when mounted dry; -but some of these when detached from the leaf--which is easily done -by gently scraping it, when dried, with a knife--present brilliant -starlike and other forms, if mounted in balsam and used with the -polariscope. There is a little danger, when placing the thin glass -upon the balsam, of forcing out the scales in the wave of matter which -is always ejected; this may be overcome by applying to the slide, -previously to placing the objects upon it, an extremely thin covering -of the balsam diluted with turpentine as before mentioned, and thus -giving them every chance of adherence; or by using the balsam with -chloroform, as before noticed. These scales are much more abundant than -was formerly supposed, and daily new specimens are discovered; so that -the student should always be on the lookout for them in his researches -in the vegetable world. - -Most classes of objects, and the treatment they require when mounting -them in balsam, have now been considered. The next chapter will be -devoted to the preservative liquids, and the best methods of using -them. - - - - -CHAPTER IV. - -PRESERVATIVE LIQUIDS, ETC., PARTICULARLY WHERE CELLS ARE USED. - - -There are many objects which would lose all their distinctive -peculiarities if allowed to become dry, especially those belonging -to the fresh-water Algæ, many animal tissues, and most of the very -delicate animal and vegetable substances in which structure is to be -shown. These must be preserved by immersion in some fluid; but it is -evident that the fluid must be suited to the kind of matter which it -is intended to preserve. As it often requires much study and trouble -to _obtain_ microscopic objects of this class, it is well that their -_preservation_ should be rendered as perfect as possible; and for this -reason the CELLS, or receptacles of the fluids, should be so closed -that all possibility of escape should be prevented. The accomplishment -of this is not so easy a matter as it might appear to the inexperienced. - -Before giving any directions as to the manipulation required in -mounting the objects, we must consider the different _liquids_ and -_cells_ which are requisite for their preservation. Of the former there -are a great number, of which the principal may be mentioned. - -DISTILLED WATER is strongly recommended by many for Diatomaceæ and -other Protophytes. It has been, however, stated that confervoid growths -often disturb the clearness of the liquid, and on this account various -additions are made to it. A lump of camphor is often left in the -bottle, so that the water may dissolve as much as possible. One grain -of bay-salt and one of alum are added to each ounce of water; or a drop -or two of creosote shaken up with the ounce of water, which should be -afterwards filtered. These additions are often made; perhaps each of -them good for certain objects. - -GLYCERINE.--Some affirm this to be one of the best preservative -liquids, especially for vegetable objects; but others think that it is -much better when diluted with two parts of camphor-water, prepared as -above.[E] - - [E] Dr. Carpenter says:--“Glycerine has a solvent power for - carbonate of lime, and should not be employed when the - object contains any calcareous structure. In ignorance - of this fact, the author (Dr. C.) employed glycerine to - preserve a number of remarkably fine specimens of the - pentacrinoid larva of the Comatula, whose colours he was - anxious to retain; and was extremely vexed to find, when - about to mount them, that their calcareous skeletons had so - entirely disappeared, that the specimens were completely - ruined.” - -GLYCERINE AND GUM.--This is also believed to be a very good liquid for -vegetable tissues, and is thus prepared:-- - - Pure gum-arabic 1 oz. - Glycerine 1 ” - Water (distilled) 1 ” - Arsenious acid 1½ grains. - -Dissolve the arsenious acid in the cold water, then the gum, add the -glycerine, and mix without bubbles. - -DEANE’S COMPOUND.--This is usually deemed about the best medium for -preserving Algæ, mosses, &c., and is thus prepared:--Soak 1 oz. of best -gelatine in 4 oz. of water until the gelatine becomes soft, when 5 oz. -of honey heated to boiling-point are added; boil the mixture, and when -it has cooled, but not enough to become stiff, add ½ oz. rectified -spirit with which 5 or 6 drops of creosote have been well mixed, and -filter the whole through fine flannel. This compound when cold forms a -stiff jelly, the use of which will be described elsewhere. - -GLYCERINE JELLY.--This mixture closely resembles the above, but as the -composition differs a little it may be mentioned here. It is strongly -recommended by Mr. Lawrance in the _Microscopic Journal_, where he -states “that the beautiful green of some mosses mounted two years -ago, is still as fresh as the day they were gathered;” and that this -is the only medium he knows which will preserve the natural colour of -vegetable substances. He takes a quantity of Nelson’s gelatine, soaks -it for two or three hours in cold water, pours off the superfluous -water, and heats the soaked gelatine until melted. To each fluid ounce -of the gelatine, _whilst it is fluid but cool_, he adds a fluid drachm -of the white of an egg. He then boils this until the albumen coagulates -and the gelatine is quite clear, when it is to be filtered through fine -flannel, and to each ounce of the clarified solution add 6 drachms of a -mixture composed one part of glycerine to two parts of camphor-water. - -GOADBY’S FLUID.--This is much used in the preservation of animal -objects; and seldom, if ever, acts upon the colours. It is thus -prepared--Bay salt, 4 oz.; alum, 2 oz.; corrosive-sublimate, 4 grains. -Dissolve these in two quarts of boiling water and filter. For delicate -preparations some recommend that this mixture be reduced by the -addition of an equal quantity of water; but where there is bone or -shell in the object the above acts injuriously upon it, in which case -this fluid may be used:--Bay-salt 8 oz., corrosive sublimate 2 grains, -water 1 quart. - -THWAITES’ LIQUID.--This is recommended for the preservation of -Algæ, &c., as having little or no action on the colour, and is thus -prepared:--Take one part of rectified spirit, add drops of creosote -enough to saturate it; to this add sixteen parts of distilled water and -a little prepared chalk, and filter. When filtered, mix with an equal -quantity of camphor-water (as before mentioned), and strain through -fine muslin before using. - -CHLORIDE OF ZINC SOLUTION.--In the “Micrographic Dictionary” this is -stated to be “perhaps the best preservative known for animal tissues.” -Persons of great experience, however, have given a very different -opinion; but it is certainly very useful in many cases where a small -degree of coagulating action is not injurious. It is used of strengths -varying according to the softness of the parts to be preserved; the -average being 20 grains of the fused chloride to 1 oz. of distilled -water. To keep this liquid a lump of camphor may be left floating in -the bottle. I have heard complaints that this mixture becomes turbid -with keeping, but I think this must only be the case when some impurity -has got into the bottle. - -CARBOLIC ACID.--This substance has not been known long enough to -warrant any decided opinion upon its merits. A solution of 1 part of -acid to 20 of water has been recommended on account of its antiseptic -properties. - -CASTOR OIL.--This is a very useful preservative for crystals and -other objects. Many salts are quite destroyed when Canada balsam is -used with them; but very few are acted upon by this oil. To use it, -it must be dropped in a sufficient quantity to cover the crystal or -object to be preserved with a thin coating of oil. It may be necessary -sometimes to spread it with a needle or other instrument. The thin -glass should then be carefully placed upon it, so that all air may -be excluded; and should any oil be forced out, owing to the quantity -used being too great, it must be removed with blotting paper. When -the edge of the thin glass cover and the surrounding parts of the -slide are as clean as possible, a coating of sealing-wax varnish or -liquid glue must be applied and allowed to dry. A second or even a -third coating may be required, but not before the previous cover is -quite dry. These varnishes, however, are very brittle, and it is much -safer, as a finish, to use one of the tougher cements--gold-size, for -instance--which will render it doubly secure. - -The above are the principal liquids, &c., used for preserving objects -in cells. The different cells may be here mentioned; and it is -recommended that these should always be kept some time before use in -order that the cement may become perfectly dry; and care must be taken -that no cement be used on which the preservative liquid employed has -any action whatever. - -CEMENT CELLS.--Where the object is not very thick, this kind of cell -is generally used. They are easily made with the turntable before -described; but when the objects to be preserved are _very_ minute, -these cells need not be much deeper than the _ordinary_ circle of -cement on the slide. When, however, a comparatively great depth is -required, it is sometimes necessary to make the wall of the cell as -deep as possible, then allow it to dry and make another addition. Of -these cements gold-size is one of the most trustworthy, and may be -readily used for the shallow cells. The asphaltum and india-rubber, -before noticed, I have found very durable when well baked, and -exceedingly pleasant to work with. It may be used of such a thickness -as to give space for tolerably large objects. Black japan also is much -used. Many cements, however, which are recommended by some writers, -are worse than useless, owing to the brittleness which renders their -durability uncertain, as sealing-wax varnish, liquid-glue, &c. - -The student may feel himself at a loss in choosing the cement which -will give him the _safest_ cells, many of them becoming partially -or wholly dry in a year or two, as stated in another place. I can -only give him a few general directions, and he must then use his own -judgment. Of course it would be lost labour to employ any cement upon -which the preservative liquid has _any action whatever_. It is also a -good rule to avoid those in whose composition there are any particles -which do not become a thorough and intimate portion, as these unreduced -fragments will almost certainly, sooner or later, prepare a road by -which the liquid will escape; and, lastly, whatever cement he uses, the -cells are always better when they have been kept a short time before -use, as already stated. - -GUTTA-PERCHA RINGS have been recommended by some, as affording every -facility for the manufacture of cells for liquids; but they cannot be -recommended, as, after a certain length of time, they become so brittle -as to afford no safeguard against ordinary accidents. - -Often the cells must necessarily be of a large size, and for this -reason are made by taking four strips of glass of the thickness and -depth required, and grinding the places where these are to meet with -emery, so as to form a slightly roughened but flat edge. The glass -strip must also be ground on the side where it meets the plate, and -each piece cemented with the marine glue mentioned in Chapter I. in the -following manner:--On that part of the glass to which another piece -is to be attached should be laid thin strips of the glue; both pieces -must then be heated upon a small brass table, with the aid of the -spirit-lamp, until the strips become melted; the small piece is then -to be taken up and placed upon the spot to which it is to be attached, -and so on until the cell is completed. It will be found necessary to -spread the glue over the surface required with a needle or some other -instrument, so that an unbroken line may be presented to the wall of -the cell, and no bubbles formed. Too great a heat will “burn” the -marine-glue, and render it brittle; care must be therefore taken to -avoid this. - -When shallow cells are required, those which are made by grinding -a concavity in the middle of an ordinary slide will be found very -convenient. The concavities are cut both circular and oblong; and the -surface being flat, the cover is easily fastened upon it. These are now -cheap, and are very safe as to leakage. - -Circular cells with a flat bottom used to be made by drilling a hole -through glass of the required thickness, and fixing this upon an -ordinary slide with marine-glue; but the danger of breakage and the -labour were so great that this method is seldom used now, and, indeed, -the rings about to be mentioned do away with all necessity of it. - -GLASS RINGS.--Where any depth is required, no method of making a cell -for liquids is so convenient as the use of glass rings, which are now -easily and cheaply procurable. They are made of almost every size and -depth, and, except in very extraordinary cases, the necessity for -building cells is completely done away with. These rings have both -edges left roughened, and consequently adhere very well to the slide, -this adherence being generally accomplished by the aid of marine glue, -as before noticed with the glass cells. Gold-size has been occasionally -used for this purpose; and the adherence, even with liquid in the -cell, I have always found to be perfect. This method has the advantage -of requiring no heat, but the gold-size must be perfectly dry, and -the ring must have been fixed upon the slide some time before use. -Canada balsam has also been used for the same purpose, but cannot be -recommended, as when it is perfectly dry it becomes so brittle as to -bear no shock to which the slide may be ordinarily exposed. - -These are the cells which are mostly used in this branch of microscopic -mounting. The mode of using them, and the different treatment -which certain objects require when intended to be preserved in the -before-mentioned liquids, may now be inquired into. - -I may mention, however, that this class of objects is looked upon by -many with great mistrust, owing to the danger there is of bubbles -arising in the cells after the mounting has been completed, even for -years. I know some excellent microscopists who exclude all objects -in cells and preservative liquids from their cabinets, because they -say that eventually almost all become dry and worthless; and this is -no matter of surprise, for many of them do really become so. Perhaps -this is owing to the slides being sold before they could possibly be -thoroughly dry. As to the air-bubbles, I shall have something to say -presently. - -We will now suppose the cell employed is made by placing a glass -ring upon the slide with marine glue or gold-size, and is quite dry. -Around the edge of the cleaned thin glass which is to cover it, I -trace with a camel-hair pencil a ring of gold-size, and also around -the edge of the cell to which it is to adhere. Dr. Carpenter objects -to this, as rendering the later applications of the gold-size liable -to “run in.” All danger of this, however, is completely done away with -by leaving the slide and cover for awhile until the cement becomes -partially “fixed,” but still adhesive enough to perform its function -(Chapter II.). With many slides this is not accomplished in less than -twenty-four hours, even if left two or three days no injury whatever -ensues; but with other kinds an hour is too long to leave the exposed -cement, so that the operator must use his own discretion. The liquid -required may be drawn up by the mouth into the pointed tube mentioned -in Chapter I., and then transferred to the cell. In the various books -of instruction, the object is now to be placed in the cell; this, -however, I think a great mistake, as another process is absolutely -necessary before we advance so far. The cell, full of liquid, must -be placed under the receiver of an air-pump, and the air withdrawn. -Almost immediately it will be perceived that the bottom and sides of -the cell are covered with minute bubbles, which are formed by the air -that is held in suspension by the liquid. The slide may now be removed, -and the bubbles may require the aid of a needle or other point to -displace them, so obstinately do they adhere to the surface of the -glass. This process may be then repeated, and one cause, at least, of -the appearance of bubbles in cells of liquid will be got rid of. The -object to be mounted should also be soaked in one or two changes of the -preservative liquid employed, and, during the soaking, be placed under -the air-pump and exhausted. It may then be transferred to the cell, -which will probably cause the liquid to overflow a little. The cover -with the gold size applied to the edge must then be carefully laid upon -the cell, and slightly pressed down, so that all air-bubbles may be -displaced. The two portions of gold-size will now be found to adhere -wherever the liquid does not remain, although the whole ring may have -been previously wet. The outer edge of the thin glass and cell must -now be perfectly dried, and a coating of gold-size applied. When this -is dry, the process must be repeated until the cement has body enough -to protect the cell from all danger of leakage. When some preservative -liquids are used, a scum is frequently found upon the surface when -placed in the cell, which must be removed immediately before the cover -is laid upon it. - -I believe this method to be perfectly secure against leakage when -carefully performed; and some of my friends have told me that their -experience (some years) has been equally satisfactory. - -In using some of the particular kinds of preservative liquids, it will -be found necessary to make slight change in the manipulation. This will -be best explained by mentioning a few objects, and the treatment they -require. - -For the preservation of the Mosses, Algæ, &c., Deane’s compound is -much used, and considered one of the best media. The specimen to be -mounted should be immersed in the compound, which must be kept fluid -by the vessel containing it being placed in hot water. In this state -the whole should be submitted to the action of the air-pump, as it is -not an easy matter to get rid of the bubbles which form in and around -the objects. The cell and slide must be warmed; and heat will also -be necessary to render the gelatine, &c., fluid enough to flow from -the stock-bottle. The cell may then be filled with the compound, and -the specimen immersed in it. A thin glass cover must then be warmed, -or gently breathed upon, and gradually lowered upon the cell, taking -care, as with all liquids, that no bubbles are formed by the operation. -The cover may be fixed by the aid of gold-size, Japan, or any of the -usual varnishes, care being taken, as before, that all the compound is -removed from the parts to which the varnish is intended to adhere. - -The glycerine jelly of Mr. Lawrance, before mentioned, requires almost -a similar treatment. “The objects to be mounted in this medium should -be immersed for some time in a mixture of equal parts of glycerine -and dilute alcohol (six of water to one of alcohol). The bottle of -glycerine jelly must be placed in a cup of hot water until liquefied, -when it must be used like Canada balsam, except that it requires less -heat. A ring of asphaltum varnish round the thin glass cover completes -the mounting.” - -The Infusoria (see Chapter III.) are sometimes preserved in liquid; -but present many difficulties to the student. Different kinds require -different treatment, and consequently it is well, when practicable, to -mount similar objects in two or more liquids. Some are best preserved -in a strong solution of chloride of calcium, others in Thwaites’ -liquid, whilst a few keep their colour most perfectly when in glycerine -alone. Many of them, however, are so very transparent that they present -but faint objects for ordinary observance. The Desmidiaceæ require -somewhat similar treatment, and may be mentioned here. The solution of -chloride of calcium has been strongly recommended; but no preservative -liquid seems to be without some action upon them. Both of the above -classes of objects should be mounted in shallow cells, so as to allow -as high a microscopic power as possible to be used with them. - -Many of the ZOOPHYTES which are obtained on our sea-coasts are well -preserved by mounting in cells, in the manner before mentioned, with -Goadby’s fluid, or distilled water with one of the additions noticed -amongst the preservative liquids. For examination by polarized light, -however, they are usually mounted in balsam (see Chapter III.), whilst -those in cells present a more natural appearance as to position, &c., -for common study. - -As to the use of preservative liquids with the Diatomaceæ there are -various opinions. Some experienced microscopists say that there is -little or no satisfaction in mounting them in this way. Dr. Carpenter, -however, explains this difference by his instructions as to what method -should be used when certain ends are desired. He says: “If they can -be obtained quite fresh, and it be desired that they should exhibit -as closely as possible the appearance presented by the living plants, -they should be put up in distilled water within cement-cells; but if -they are not thus mounted within a short time after they have been -gathered, about a sixth part of alcohol should be added to the water. -If it be desired to exhibit the stipitate forms in their natural -parasitism upon other aquatic plants, the entire mass may be mounted -in Deane’s gelatine in a deeper cell; and such a preparation is a very -beautiful object for the black-ground illumination. If, on the other -hand, the minute structure of the siliceous envelopes is the feature -to be brought into view, the fresh diatoms must be boiled in nitric or -hydrochloric acid” (which process is fully described in Chapter II.). -It is very convenient to have many of these objects mounted by two -or more of the above methods; and if they are to be studied, this is -indispensable. Mr. Hepworth once showed me about one hundred slides -which he had mounted in various ways, for no other purpose than the -study of the fly’s foot. - -My friend, Mr. Rylands, successfully mounts the diatoms in the state -in which he finds them, and gave me the following method as that which -he always employs. He says that he has had no failures, and hitherto -has found his specimens unchanged. Take a shallow ring cell of asphalt -or black varnish (which must be at least three weeks old), and on the -cell, whilst revolving, add a ring of benzole and gold-size mixed in -equal proportions. In a minute or two pure distilled water is put in -the cell until the surface is slightly convex. The object having been -already floated on to the cover (the vessel used for this purpose being -an ordinary indian-ink palette), is now inverted and laid carefully -upon the water in the cell. By these means the object may be laid down -without being removed. The superfluous moisture must not be ejected by -pressure, but a wetted camel-hair pencil, the size made in an ordinary -quill, being partially dried by drawing through the lips, must be -used repeatedly to absorb it, which the pencil will draw by capillary -attraction as it is very slowly turned round. When the cover comes in -contact with the benzole and gold-size ring, there is no longer any -fear of the object being removed, and a slight pressure with the end -of the cedar stick of the pencil will render the adhesion complete, -and cement the cover closely and firmly to the cell. When dry, an outer -ring of asphalt makes the mounting neat and complete. - -The _Fungi_ have been before mentioned; but it may be here stated that -some few of the minute forms are best preserved in a very shallow cell -of liquid. For this purpose creosote-water may be advantageously used. - -The _antennæ_ of insects have been before noticed as being very -beautiful when mounted in balsam. This is readily accomplished when -they are large; but those of the most minute insects are much more -difficult to deal with, and are less liable to injury when put up in -fluid. _Goadby’s Fluid_ serves this purpose very well; but, of course, -the object must be thoroughly steeped in the liquid before it is -mounted, for a longer or shorter time according to the thickness. - -The _eggs of insects_ afford some worthy objects for the microscope, -amongst which may be mentioned those of the common cabbage butterflies -(small and great), the meadow-brown, the puss-moth, the tortoiseshell -butterfly, the bug, the cow-dung fly, &c. These, however, shrivel up on -becoming dry, and must, therefore, be preserved in some of the fluids -before mentioned. To accomplish this no particular directions are -required; but the soaking in the liquid about to be employed, &c., must -be attended to as with other objects. - -_Glycerine_ may be advantageously used for the preservation of various -insects. These should first be cleaned with alcohol to get rid of all -extraneous matter, and then, after soaking in glycerine, be mounted -with it like other objects. This liquid may also be used for the -Entomostraca, which offer a wide field for study. They are to be -found abundantly in ponds of stagnant water, &c. Some insects, such -as May-flies, &c., are, however, often preserved by immersion in a -solution of one part of chloride of calcium in three or four parts of -water; but this has not been recommended amongst the “preservative -liquids,” as the colour, which is often an attractive quality of this -class of objects, is thereby destroyed. - -We have now noticed the treatment which must be applied to those -objects which are to be preserved in liquids and cells. We may here -state that all slides of this kind should be examined at short -intervals, as they will be found now and then to require another -coating of varnish round the edge of the thin glass cover to prevent -all danger of leakage. The use of the air-pump, in the first instance -(as before recommended), and this precaution as to the varnish, will -render the slides less liable to leakage and air-bubbles, which so very -frequently render them almost worthless. - - - - -CHAPTER V. - -SECTIONS AND HOW TO CUT THEM, WITH SOME REMARKS ON DISSECTION. - - -Many objects are almost worthless to the microscopist until the -extraneous matter is removed from them; and this is frequently -difficult in the extreme to perform satisfactorily. As an instance, -certain Foraminifera may be mentioned in which the cells are placed -one upon another, consequently the object must be reduced to a certain -degree of _thinness_ before a single uniform layer of these cells can -be obtained to show something of the internal arrangements. - -Most animal and vegetable forms require an examination of the separate -parts before much can be known about them. The mass must be divided -into separate portions, each part intended to be preserved being -cleaned from the useless matter with which it is surrounded. It will -frequently be found necessary to make thin sections, which from a very -tender substance is no easy matter; and much patience will be necessary -to attain anything like proficiency. - -This making of sections was not until very recently entered into by -many except those belonging to the medical profession, but I do not see -why this should be so, as much may be accomplished by a persevering -and interested mind where there is time for entering into the subject. -I will therefore make an attempt to give some instructions on this -subject also. We will first consider the cutting of sections from hard -substances, in which the ordinary knife, chisel, &c., are of no avail. -Most of these require no particular care in mounting, but are placed in -balsam like the other objects noticed in Chapter III.: where, however, -any special treatment is necessary it will be commented upon as we -proceed. - -SHELLS, &C.--It is seldom, if ever, necessary to possess apparatus -for this process except a small thin saw made with a steel blade, for -which a piece of watch-spring serves very well; a fine stone such as -is used for sharpening pen-knives; and two smooth leather strops, -one of which is to be used with putty-powder to polish the section -after grinding, and the other dry, to give the final surface. It is, -however, very convenient to have three or four files of different -degrees of fineness. The shell, if very thick, may be divided by -using the watch-spring saw; and this section may then with ordinary -care be rubbed down with water on the stone until one side of it is -perfectly flat. When this is accomplished it must be again rubbed with -putty-powder upon the strop, and finally upon the other strop without -the powder. This surface will then be finished and must be firmly -united to the slide in the position it is intended to occupy. To do -this a small quantity of Canada balsam may be dropped upon the middle -of the slide and heated over the lamp until on cooling it becomes hard; -but this must be stopped before it is rendered brittle. Upon this the -polished surface must be laid, and sufficient heat applied to allow -the object to fall closely upon the slide, when slight pressure may be -used to force aside all bubbles, &c. On cooling, the adherence will be -complete enough to allow the same grinding and polishing upon the upper -surface which the lower received. Whilst undergoing this, the section -must be examined from time to time to ascertain whether the necessary -degree of thinness has been reached. When this is the case the section -should be washed thoroughly and dried. It must then be covered, which -is best done by using the ordinary Canada balsam, as recommended in -Chapter III. - -Sections of some exquisitely beautiful objects are cut with much less -trouble than the above. The Orbitolite, for instance, may be prepared -in this manner. Take the object and by pressure with the finger rub -the side upon a flat and smooth sharpening stone with water until the -portion is reached which it is wished to show. The strength of the -object will easily allow this to be accomplished with ordinary care. -This side may then be attached to the glass slide with heated balsam, -as above described, and the object may then be gently rubbed down to -the degree of thinness required to show it to the best advantage. -After removing all disengaged matter from the object by washing and -thoroughly drying, it may be mounted in balsam in the usual manner, -when it is equally beautiful as a transparent or opaque object. From -this it will be seen that in many instances where a smooth stone is -found sufficient for the work (which is often the case when the section -is mounted in balsam) the final process of polishing advised above -may be dispensed with, as in the Orbitolite, Nummulite, &c., &c. It -is quite necessary that the stones on which the objects are rubbed -be _perfectly flat_, otherwise one side must be acted upon before -the other, and it will be found impossible to attain anything like -uniformity. Where it is not practicable to cut a section and the object -is very thick, a coarse stone may be first used to reduce it and the -smoother afterwards. - -The consideration of the cutting of sections from shells would scarcely -be deemed complete without some mention of what Dr. Carpenter terms the -decalcifying process. Muriatic acid is diluted with twenty times its -volume of water, and in this the shell is immersed. After a period, -differing according to the thickness of the shell, the carbonate of -lime will be dissolved away, and a peculiar membrane left, showing -the structure of the shell very perfectly. This may be mounted dry, -in balsam, or sometimes in liquid, according to the appearance of -the object; but no rule can be given. The discretion of the student, -however, will enable him to choose the most suitable method. - -From some shells it is easy to divide thin plates, or “laminæ,” which -require nothing but mounting in Canada balsam to show the texture very -well. In working, however, with those which are “pearly,” it will -be found that experience and patience are needed, as they are very -brittle and peculiarly hard; but a little practice will overcome these -difficulties. - -Amongst the Echinodermata, which include the star-fishes, -sea-hedgehogs, &c., there are many whose outer surface is covered with -“spines,” or thin projections. Some of these are sharp and thorn-like, -others blunt, longer or shorter, and, indeed, of endless variety. In -many of these, when a section is made, rings are seen which have a -common centre, with radiating supports, resembling sections of some of -the woods. These are very beautiful objects, and methods of procuring -them may now be considered. It is the best to cut as thin a section -as can safely be got with the watch-spring saw first, when the smooth -“sharpening stone” may be used to polish one side, which is easily -accomplished with water only. When this is effected, it must be washed -clean, and _thoroughly_ dried, and then may be united to the slide in -the same manner as before recommended for the Orbitolite, &c. If it is -ever necessary to displace it on account of inequalities, bubbles, or -other remediable fault, this may be done by warming the slide; though -too much heat must be avoided, otherwise fresh bubbles will certainly -be produced. The covering with thin glass, balsam, &c., will present no -difficulty to the student; but he must remember that the transparency -is somewhat increased by this last operation. - -_Corals_ are often treated in this way, in order to reveal their -structure. Except, however, the student has had much practice, he will -often find this a most difficult task, as many of them are exceedingly -brittle. He will find the method before described equally applicable -here, and should take both horizontal and vertical sections. - -COAL.--This substance is one of the most interesting objects to the -microscopist. It is, of course, of a vegetable origin; and though this -is in many cases of such minute separate portions as to have lost -all appearance of vegetation, yet it is very frequently met with -in masses, bearing the form, even to the minute markings, of wood, -in various directions. To see this and prepare it for microscopic -research, a suitable piece of coal must be obtained; but in every case -the cutting and preparation of these sections require great care and -skill. Sometimes the coal is first made smooth on one side, fastened to -the glass, reduced to the requisite degree of thinness, and finished -in the method before described. This mode of treating it is sometimes, -however, very tantalizing, as, at the last moment, when the section -is about thin enough, it often breaks up, and so renders the trouble -bestowed upon it fruitless. The dark colour and opacity of coal render -an extraordinary thinness necessary, and so increase the liability to -this accident. - -Perhaps the best method which can be pursued is that recommended in the -“Micrographic Dictionary,” which is as follows:--“The coal is macerated -for about a week in a solution of carbonate of potash; at the end of -that time it is possible to cut tolerably thin slices with a razor. -These slices are then placed in a watch-glass with strong nitric acid, -covered and gently heated; they soon turn brownish, then yellow, when -the process must be arrested by dropping the whole into a saucer of -cold water, else the coal would be dissolved. The slices thus treated -appear of a darkish amber colour, very transparent, and exhibit the -structure, when existing, most clearly. We have obtained longitudinal -and transverse sections of coniferous wood from various coals in this -way. The specimens are best preserved in _glycerine_ in cells; we find -that spirit renders them opaque, and even Canada balsam has the same -defect. Schulz states that he has brought out the cellulose reaction -with iodine, in coal treated with nitric acid and chlorate of potash.” - -_Cannel-coal_ is so close and firm in its structure as to be much used -instead of jet in the manufacture of ornaments: it takes a beautiful -polish, and consequently presents the student with none but ordinary -difficulties in getting sections of it. Its formation is somewhat -different from that of coal, sometimes showing the transition very -clearly. - -In _flint_ there are often found remains of sponges, shells, -Diatomaceæ, &c.; but to show these well, sections must be cut and -polished by the lathe and wheel of the lapidary, which the microscopic -student seldom possesses. Thin chippings may, however, be made, which -when steeped in turpentine and mounted in balsam, will frequently show -these remains very well. - -_Teeth_ are very interesting objects to all microscopists, more -especially to those who give much study to them; as the class of animal -may very frequently be known from one solitary remaining tooth. To -examine them thoroughly, it is necessary to cut sections of them; but -this is rather difficult to perform well, and needs some experience. -Some instructions, however, will at least lessen these difficulties, -and we will now endeavour to give them. - -It is generally thought that Canada balsam injures the finer markings -of these sections, consequently, they are almost invariably mounted -_dry_. A thin piece is first cut from the tooth with the saw of -watch-spring before mentioned, if possible; but should the substance be -too hard for this, the wheel and lathe must be used with diamond dust. -If this cannot be procured, there is no alternative but to rub down the -whole substance as thin as practicable on some coarse stone or file. -The surface will then be rough; but this may be much reduced by rubbing -upon a flat sharpening stone with the finger, or a small piece of -gutta-percha, upon the object to keep it in contact. The scratches may -be much lessened by this, but not so thoroughly removed as microscopic -examination requires in dry sections. It must, therefore, be polished -with the putty-powder and dry strop, as recommended in the working of -the shell-sections. The other side of the section of the tooth may then -be rubbed down to the requisite thinness, and polished in the same -manner, when the dust and other impurities must be removed by washing, -after which the section must be carefully dried and mounted. Some of -these sections are equally interesting as opaque or transparent objects. - -The dentine of the teeth may be decalcified by submersion of the -section in dilute muriatic acid; after drying and mounting in Canada -balsam it presents a new and interesting appearance, showing the enamel -fibres very beautifully when magnified about three hundred diameters. A -friend tells me that after submersion of the _whole tooth_ in the acid -he has been able to cut sections with a razor. - -SECTIONS OF BONE.--With the aid of the microscope few fragmentary -remains have proved so useful to the geologist and students of the -fossil kingdom as these. From a single specimen many of our naturalists -can tell with certainty to what _class_ of animal it has once belonged. -To arrive at this point of knowledge much study is necessary, and -sections of various kinds should be cut in such a manner as will best -exhibit the peculiarities of formation. The methods of accomplishing -this will now be considered. It may, however, be first mentioned that -the chippings of some bones will be found useful now and then, as -before stated with flint, though this is by no means a satisfactory -way of proceeding. Sometimes the bones may be procured naturally so -thin that they may be examined without any cutting; and only require -mounting _dry_, or in _fluid_, as may be found the best. - -When commencing operations we must provide the same apparatus as is -needed in cutting sections of teeth, before described. A fine saw, like -those used for cutting brass, &c.; two or three flat files of different -degrees of coarseness; two flat “sharpening” stones; and a leather -strop with putty-powder for polishing. As thin a section as possible -should first be cut from the part required by the aid of the fine saw; -and it is better when in this state to soak it for some short time -in camphine, ether, or some other spirit to free it from all grease. -With the aid of a file we may now reduce it almost to the necessary -degree of thinness, and proceed as before recommended with teeth. The -“sharpening” stone will remove all scratches and marks sufficiently -to allow it to be examined with the microscope to see if it is ground -thin enough; and if it is to be mounted _dry_ we must polish it with -putty-powder and water upon the strop to as high a degree as possible, -and having washed all remains of polishing powder, &c., from the -section we must place it upon the slide and finish it as described in -Chapter II. - -If the bone is not sufficiently hard in its nature to bear the above -method of handling whilst grinding and polishing--as some are far more -brittle than others--as thin a section as possible must first be cut -with the saw, and one surface ground and polished. The piece must then -be dried and united to the glass by heated balsam in the same manner as -shells, &c. After which the superabundance of balsam must be removed -from the glass; then rub down upon the stone and strop as before. -When the polishing is completed the whole slide must be immersed in -chloroform, ether, or some other spirit, to release and cleanse the -section, when it may be mounted as the one above mentioned. - -Some have recommended a strong solution of isinglass to affix the -half-ground teeth or bones to the glass as causing them to adhere very -firmly and requiring no heat, and also being readily detached when -finished. - -The reason why the sections of bone are usually mounted _dry_ is -that the “_lacunæ_,” bone cells, and _canaliculi_ (resembling minute -canals) show their forms, &c., very perfectly in this state, as -they are hollow and contain air, whereas if they become filled with -liquid or balsam--which does sometimes occur--they become almost -indistinguishable. There are some dark specimens, however, where the -cells are already filled with other matter, and it is well to mount -these with balsam and so gain a greater degree of transparency. - -To gain a true knowledge of the structure of bone, sections must be cut -as in wood, both transversely and longitudinally; but with _fossil_ -bones, without the lapidary’s wheel, &c., it is a laborious task, and -indeed can seldom be properly accomplished. In this place, also, it may -be mentioned that by submitting bone to the action of muriatic acid -diluted ten or fifteen times with water, the lime, &c., is dissolved -away and the cartilage is left, which may be cut into sections: in -_caustic potash_ the animal matter is got rid of. Both of these -preparations may be mounted in fluid. - -The method of cutting thin sections of bone may be also employed with -the stones of fruit, vegetable ivory and such like substances; many of -which show a most interesting arrangement of cells, especially when -the sections are transverse. Most of these objects present a different -appearance when mounted _dry_ to that which they bear when _in balsam_, -owing to the cells becoming filled; and to arrive at a true knowledge -of them we must have a specimen mounted in both ways. - -To those who study polarized light, few objects are more beautiful than -the sections of the different kinds of horn. We will briefly inquire -into the best method of cutting these. There are three kinds of horn, -the first of which is hard, as the stag’s, and must be cut in the same -manner as bone. The second is somewhat softer, as the cow’s. The third -is another and still softer formation, as the “horn” (as it is termed) -of the rhinoceros. In cutting sections of the two last we should -succeed best by using the machine invented for these purposes which I -shall shortly describe when the method of cutting wood is considered. -To aid us in this when the horn is hard it must be boiled for a short -time in water, when the cutting will be more easily accomplished. The -sections should be both transverse and longitudinal, those of the -former often showing cells with beautiful crosses, the colours with -the selenite plate being truly splendid. Of this class the rhinoceros -horn is one of the best; but the buffalo also affords a very handsome -object. The cow’s, and indeed almost every different kind of horn, well -deserves the trouble of mounting. Whalebone, when cut transversely, -strongly resembles those of the third and softer formation. All these -are best seen when mounted in Canada balsam, but care must be taken -that they have been thoroughly dried after cutting, and then steeped in -turpentine. - -An interesting object may also be procured from whalebone by cutting -long sections of the hairs of which it is composed. Down the centre -of each hair we shall find a line of cells divided from one another -very distinctly. And (as recommended in the “Micrographic Dictionary”) -if whalebone be macerated twenty-four hours in a solution of caustic -potash it will be softened, and by afterwards digesting in water, the -outer part will be resolved into numerous transparent cells, which will -show more plainly the structure of this curious substance. - -In a former chapter, hairs were mentioned, their many and interesting -forms, and their beauty when used with polarized light. The sections of -them, however, are no less a matter of study, as this mode of treatment -opens to sight the outer “casing,” and the inner substance somewhat -resembling the pith of plants. - -It would be out of place to enter into the description of the different -forms met with; but the ways in which sections are to be procured -may be glanced at. If transverse sections are required, some place a -quantity of hairs betwixt two flat pieces of cork, which by pressure -hold them firmly enough together to allow the required portions to be -cut with a razor. Others take a bundle of the hairs and dip it into gum -or glue, which gives it when dry a solidity equal to wood. Sections of -this are then cut with the machine mentioned a little further on, and -these may be mounted in balsam. The human hair is easily procured in -the desired sections by shaving as closely as possible a second time -and cleansing from the lather, &c., by carefully washing. Most hairs, -however, should be examined both transversely and longitudinally. It -is not difficult to procure the latter, as we may generally split them -with the aid of a sharp razor. In a great number of hairs there is a -quantity of greasy matter which must be got rid of by soaking in ether -or some other solvent before mounting. - -We may next consider the best method of procuring _sections of wood_, -which must be cut of such a degree of thinness as to form transparent -objects, and so display all the secrets of their structure. There -is no monotony in this study, as the forms are so various, and the -arrangement of the cells and woody fibre so different, that the -microscopist may find endless amusement or study in it. From a single -section the _class_ of trees to which it has belonged may be known, -often even when the wood is _fossil_. The apparatus best adapted for -cutting these sections is made as follows:--A flat piece of hard wood, -about six inches long, four wide, and one thick, is chosen, to which -another of the same size is firmly fixed, so as to form, in a side -view, the letter =T=. On one end of the upper surface is fastened a -brass plate, perfectly flat, in the centre of which a circular opening -is cut about half an inch in diameter. Coinciding with this opening -is a brass tube, fixed in the under side of the table (if it may be -termed so). This tube is so cut at the bottom as to take a fine screw. -Another screw is also placed at the same end of the “table,” which -works at right angles to this, so that any substance in the tube may be -wedged firmly by working this last screw. To use this instrument, the -piece of wood or other object of which a section is required must be -placed in the tube, when, by turning the screw underneath, the wood is -raised above the brass plate more or less as wished, and by using the -screw at the end, it is held firmly in the same position. With a flat -chisel the portion of the object which projects above the surface of -the brass plate may now be cut off, and by means of the bottom screw -another portion may be raised and treated in the same manner. As to -the thickness of which objects should be cut, no proper directions can -be given, as this differs so greatly that nothing but experience can -be any guide. The same thickness can be obtained by working the screw -underneath in uniform degrees, the head being marked for this purpose; -and when the substance to be cut is _very_ much smaller than the hole -in the brass plate, it may be wedged with cork. - -As this instrument is peculiarly adapted for cutting wood (though -used for other substances, as before mentioned), I shall notice a -few particulars concerning this branch of sections. It may here be -remarked, that to obtain anything like a true knowledge of the nature -of wood, it should be cut and examined in at least two directions, -_across_ and _along_. The piece of wood is often placed in spirits -for a day or two, so that all resinous matter may be dissolved out of -it; it must then be soaked in water for the same length of time, so -as to soften and render it easy to cut. Sections are obtained in the -manner described above, but often curl to such a degree as to make it -necessary to immerse them in water, from which they may be taken and -dried under slight pressure. They are often mounted _dry_, and require -no care beyond other objects, as in Chapter II. Some, however, are -best mounted in balsam, particularly the long sections when used for -the polariscope; these must be soaked in turpentine, and the greatest -care taken that all air bubbles are got rid of. Others are thought -to be most useful when mounted in shallow cells with some of the -_preservative liquids_ mentioned in Chapter IV.--weak spirit and water, -chloride of calcium solution of the strength of one part of the salt to -three parts of distilled water, &c. - -The above “_section-cutter_” may not be within the reach of every -student, nor is it absolutely necessary; though where any _great -number_ of specimens is required it is very useful, and insures greater -uniformity in the thickness. Many employ a razor for the purpose, which -must always be kept sharp by frequent stropping. Sections of leaves -also may be procured by the same means, though, as before mentioned, -they are sometimes easily divided by stripping the coatings off with -the fingers. The cells which come to sight by cutting some of the -orchideous plants are most interesting. To cut these leaves they -may be laid upon a flat piece of cork, thus exposing the razor to no -danger of injury by coming in contact with the support. It may be -mentioned here that the _razor_ may also be used in cutting sections -of the rush, than which a more beautiful object can scarcely be found -when viewed transversely, as it shows the stellate arrangements of the -ducts to convey the liquids to the different parts of the plant very -clearly. This should be mounted _dry_. In the same way sections of the -leaf-stalks of ferns may also be cut, some of which, as Dr. Carpenter -states, show the curious ducts very beautifully, especially when cut -rather obliquely. - -When sections of the softer substances are required, no instrument -can be compared with “Valentin’s knife,” which consists of two steel -blades lying parallel with one another and attached at the lower end. -The distance of separation may be regulated at will by a small screw -near the handle. When, therefore, a section is wanted, the substance -must be cut through, and betwixt the blades a thin strip will be found, -which may be made of any thickness, according to the distance of their -separation. By loosening the screw the blades may be extended, and the -section may be floated out in water if the damp will not injure it. -The knife cuts much better if dipped in water immediately before use -and also when the substance to be operated upon is wet, or even under -water altogether; but care must be taken, after use, to clean the -blades thoroughly and oil them before laying by, if the place is at all -damp. This instrument is most useful in such subjects as anatomical -preparations where the sections are required to show the position of -the different vessels, &c.; but, as before stated, is very valuable for -all soft substances. As an instance of this, it may be mentioned, that -it is frequently used in cutting sections of sponges; but as these are -often very full of spicula, &c., it is much better to press the sponge -flat until dry, and then cut off thin shavings with a very sharp knife; -these shavings will expand when placed in water. After this they may -be laid betwixt two flat surfaces and dried, when they may be mounted -as other dry objects, or, when desirable, in balsam. - -_Valentin’s knife_ is very much used in taking sections of skin, which -are afterwards treated with potash solution, acids, &c., to bring out -in the best way the different portions. Dr. Lister’s mode, however, -of getting these is thus given in the _Microscopic Journal_:--“But -I afterwards found that much better sections could be obtained from -dried specimens. A portion of shaved scalp being placed between two -thin slips of deal, a piece of string is tied round them so as to -exercise a slight degree of compression; the preparation is now laid -aside for twenty-four hours, when it is found to be dried to an almost -horny condition. It then adheres firmly by its lower surface to one -of the slips, and thus it can be held securely, while extremely thin -and equable sections are cut with great facility in any plane that may -be desired. These sections, when moistened with a drop of water and -treated with acetic acid, are as well suited for the investigation of -the muscular tissue as if they had not been dried.” - -There are many who almost confine their attention to polarized light -and its beautiful effects. Such would not deem these efforts to aid -the student in cutting sections complete without some notice of those -which are taken from various crystals, in order to display that curious -and beautiful phenomenon, _the rings with a cross_. The arrangement of -these is somewhat changed by the crystal which affords the section; but -nitrate of potash gives two sets of rings with a cross, the long line -of which passes through both, the short line dividing it in the middle. - -The process of cutting these sections is rather difficult, but a -little care and perseverance will conquer all this. The following is -extracted from the _Encyclopædia Metropolitana_:--“Nitre crystallizes -in long six-sided prisms whose section, perpendicular to their sides, -is the regular hexagon. They are generally very much interrupted in -their structure; but by turning over a considerable quantity of the -ordinary saltpetre[F] of the shops specimens are readily found which -have perfectly transparent portions of some extent. Selecting one -of these, cut it with a knife into a plate _above_ a quarter of an -inch thick, directly across the axis of the prism, and then grind it -down on a broad wet file till it is reduced to about one quarter or a -sixth of an inch thick, smooth the surface on a wet piece of emeried -glass, and polish on a piece of silk strained very tight over a strip -of plate-glass, and rubbed with a mixture of tallow and colcothar -of vitriol. This operation requires practice. It cannot be effected -unless the nitre be applied wet and rubbed till quite dry, increasing -the rapidity of the friction as the moisture evaporates. It must be -performed in gloves, as the vapour from the fingers, as well as the -slightest breath, dims the polished surface effectually. With these -precautions a perfect vitreous polish is easily obtained. We may here -remark, that hardly any two salts can be polished by the same process. -Thus, Rochelle-salt must be finished wet on the silk, and instantly -transferred to soft bibulous linen and rapidly rubbed dry. Experience -alone can teach these peculiarities, and it is necessary to resort to -contrivances (sometimes very strange ones) for the purpose of obtaining -good polished sections of soft crystals, especially of those easily -soluble in water. - -“The nitre is thus polished on both its surfaces, which should be -brought as near as possible to parallelism.” - - [F] Sometimes the saltpetre of the shops is nitrate of _soda_, - and as this is slightly deliquescent, it is well to be - certain that we have the nitrate of _potash_, which is free - from this defect. - -Some sections of the naturally formed crystals also show the “rings” -very well,--as Iceland Spar, which gives a single ring and cross; but -the difficulty of cutting and polishing them is almost too great for -the amateur, and must be left to the lapidary. This curious phenomenon, -however, may be seen by using a plate of ice uninterruptedly formed of -about one inch in thickness. - -Before concluding these remarks on sections, I must mention a few -difficulties which may be met with, and their remedies. The foremost of -these is the softness of some objects, which have not resistance enough -in themselves to bear cutting even with the sharpest instruments. -This may often be removed by soaking in a solution of gum, and then -drying, which will render the substance firm enough to be cut, when the -sections must be steeped in water, and the gum thus got rid of. Small -seeds, &c., may be placed in wax when warmed, and will be held firmly -enough when it is again cold to allow of them being cut into sections, -&c. And, lastly, where a substitute for a microscopist’s hand-vice is -required, a cork which fits any tube large enough may be taken and -split, the object being then placed between the two parts, and the cork -thrust into the tube, a sufficient degree of firmness will be obtained -to resist any necessary cutting, &c. - -DISSECTION.--As I stated at the commencement of this chapter, no -written instructions can enable any student to become an adept in this -branch without much experience and no little study. I will, however, -describe the necessary apparatus, and afterwards mention the mode of -treatment which certain objects require. - -A different microscope is manufactured for the purpose of dissection, -most first-rate makers having their own model. The object-glasses of -many of these are simple, and consequently not expensive; but one of -the great requisites is a stage large enough to hold the trough, in -which the operation is often performed. Where this is the case it would -scarcely be worth the expense of getting a dissecting microscope if the -student were pursuing no particular study, but merely made use of the -instrument when an object to be operated upon turned up accidentally. -The ordinary form is much improved for this purpose, by having two -wooden rests placed at the sides of the microscope, upon which the -hands may be supported when working upon the stage. These should be -weighty enough to be free from danger of moving. These supports will -also be found to be a remedy against much of the weariness which -inevitably arises from having to sustain the hands as well as work -with them. The erector, as I before observed, is necessary to a young -student; but with a little practice he may work very well without it. - -We will now notice some of the instruments which are most useful in -dissection. Two or three different sizes of ordinary scissors should -be possessed, but the shapes must be modified in others for many -purposes, as those used by surgeons; a pair with the cutting parts -bent in a horizontal direction, and another pair slightly curved in -a perpendicular; so that parts of the substance operated upon may be -reached, which it would be impossible to touch with straight scissors. -One point of these is sometimes blunt, and the other acute, being -thus made very useful in opening tubular formations. Another form of -these is made, where the blades of the scissors are kept open by a -spring, the handles being pressed together by the fingers. Where it is -desirable, one or both of these handles may be lengthened to any degree -by the addition of small pieces of wood. - -THE KNIVES which are most useful are those of the smallest kind which -surgeons employ in very delicate operations. These are made about the -length of an ordinary pen-knife, and are fixed in rather long flattish -handles; some are curved inwards, like the blade of a scythe, others -backwards; some taper to a point, whilst others again are broad and -very much rounded. Complete boxes are now fitted up by the cutlers, of -excellent quality and surprisingly cheap. - -NEEDLES.--These are very useful and should be firmly fixed in handles -as recommended in Chapter I. It is convenient to have them of various -lengths and thicknesses. If curved by heating and bending to any -required shape they may be re-hardened by putting them whilst hot into -cold water. Dr. Carpenter also makes edged instruments by rubbing down -needles upon a hone. They are more pleasant to work with when _short_, -as the spring they have whilst _long_ robs them of much of their -firmness. - -A _glass syringe_ is also useful in many operations, serving not -only to cleanse the objects but to add or withdraw liquids from the -_dissecting-trough_. This trough will now be described, as many -substances are so changed by becoming dry that it is impossible to -dissect them unless they are immersed in water during the operation. -If the object is opaque and must be worked by reflected light, a small -square trough may be made to the required size of gutta-percha, which -substance will not injure the edge of the knives, &c.; but where -transparency is necessary, a piece of thin plate-glass must be taken, -and by the aid of marine glue (as explained in Chapter IV.) the sides -affixed of the required depth. As pins, &c., cannot be used with the -glass troughs and the substance must be kept extended, a thin sheet of -cork loaded with lead in order to keep it under water may be used; but -this, of course, renders the bottom opaque. When working with many thin -substances, a plate of glass three or four inches long and two wide -will serve every purpose, and be more pleasant to use than the trough. -A drop or two of water will be as much liquid as is needed, and this -will lie very well upon the flat surface. As these are the principal -apparatus and arrangements which are requisite in dissection, the -method of proceeding in a few cases may now be noticed. - -VEGETABLES.--The dissection of vegetable matter is much less -complicated than that of animal; maceration in water being a great -assistant, and in many cases removing all necessity for the use of the -knife. This maceration may be assisted by needles, and portions of -the matter which are not required may be removed by them. When, for -instance, the spiral vessels which are found in rhubarb are wanted, -some parts containing these are chosen and left in a small quantity of -water until the mass becomes soft, and this is more quickly effected -when the water is not changed. The mass must be then placed upon a -glass plate when practicable, or in the trough when large, and with -the aid of two needles the matter may be removed from the spiral -vessels, which are plainly seen with a comparatively low power; and by -conveying these to a clean slip of glass, repeating the process, and -at last washing well, good specimens may be procured. Most of these -should be mounted in some of the preservative liquids in the manner -described in Chapter IV. Many, however, may be dried on the slide, -immersed in turpentine, and then mounted in balsam; but liquid is -preferable, as it best preserves the natural appearance. Certain kinds -of vegetables require a different treatment to separate these spiral -vessels. Asparagus is composed of very hard vegetable matter, and some -have recommended the stems to be first boiled, which will soften them -to such a degree that they may easily be separated. Dilute acids are -also occasionally used to effect this; and in some instances to obtain -the _raphides_ caustic potash may be employed; but after _any_ of these -agents have been made use of, the objects must be thoroughly cleansed -with water, else the dissecting instruments (and perhaps the cell) will -be injured by the action of the remaining portion of the softening -agent. - -For the dissection of _animal tissues_ it is necessary that the -instruments be in the best order as to sharpness, &c.; and as the rules -to be observed must necessarily be somewhat alike in many instances, -the treatment required by some of the objects most frequently mounted -will now be described. We may here remark that _cartilage_ can be best -examined by taking sections, which will show the arrangement of the -cells very perfectly. This, however, is plainly seen in the mouse’s -ear without any section being necessary. Glycerine, the preservative -liquids before mentioned, and Canada balsam are all used to mount it; -but perhaps the first named may be preferred in many cases. - -MUSCLE.--This is what is commonly called the “flesh” of animals. If a -piece be laid upon the slide under the microscope, bundles of “fibres” -will be perceived, which with needles and a little patience may be -separated into portions, some of these being “striated,” or marked -with alternate spaces of dark and light. Some of the _non-striated_ -or _smooth_ class of muscle, such as is found in intestines, may be -prepared for the microscope by immersing for a day or two in nitric -acid diluted with three or four parts of water, and then separating -with needles and mounting as soon as possible. Sometimes _boiling_ is -resorted to to facilitate the separation, and occasions little or no -alteration in the material. Specimens are often taken from the _frog_ -and the _pig_, as being amongst the best, _Goadby’s solution_ being -generally used in mounting them. The muscle of insects also shows the -striæ very perfectly. - -NERVE-TISSUE.--This is seldom mounted; as Dr. Carpenter observes, “no -method of preserving the nerve-tissue has been devised which makes it -worth while to mount preparations for the sake of displaying its minute -characters,” but we will mention a few particulars to be observed in -its treatment. The nerve should be taken from the animal as soon as -possible after death, and laid upon a glass slide, with a drop or two -of serum if possible. The needles may be used to clean it, but extreme -delicacy is necessary. It will be found that the nerve is tubular -and filled with a substance which is readily ejected by very slight -pressure. When the nerve is submitted to the action of acetic acid, -the outer covering, which is very thin, is considerably contracted, -whilst the inner tube is left projecting; and thus is most distinctly -shown the nature of the arrangement. Mr. Lockhart Clarke, who has made -great researches into the structure of the spinal cord, gives a part -of his experience as follows:--He takes a perfectly fresh spinal cord -and submits it to the action of strong spirits of wine. This gives the -substance such a degree of hardness that thin sections may be readily -cut from it, which should be placed upon a glass in a liquid consisting -of three parts of spirit and one of acetic acid, which renders them -very distinct. To mount these sections, they must now be steeped in -pure spirit for two hours and afterwards in oil of turpentine, and -lastly must be mounted in Canada balsam. - -TRACHEÆ OF INSECTS, &C.--The nature of these was described in Chapter -III., but the method of procuring them was not explained, as this -clearly belongs to “dissection.” The larger tubes are readily separated -by placing the insect in water, and fixing as firmly as possible, -when the body must be opened and the viscera removed. The tracheæ may -then be cleaned by the aid of a camel-hair pencil, and floated upon a -glass, where they must first be allowed to dry, and then be mounted -in balsam. Mr. Quekett gives the following method of removing the -tracheæ from the larva of an insect:--“Make a small opening in its -body, and then place it in strong acetic acid. This will soften or -decompose all the viscera, and the tracheæ may then be well washed with -the syringe, and removed from the body with the greatest facility, -by cutting away the connections of the main tubes with the spiracles -by means of fine-pointed scissors. In order to get them upon the -slide, it must be put into the fluid, and the tracheæ floated upon -it; after which they may be laid out in their proper position, then -dried and mounted in balsam.” If we wish them to bear their _natural_ -appearance, they must be mounted in a cell with Goadby’s fluid; but -the structure is _sometimes_ well shown in specimens mounted dry. As -before mentioned, these tracheæ terminate on the outside in openings -termed spiracles, which are round, oblong, and of various shapes. Over -these are generally a quantity of minute hairs, forming a guard against -the entrance of dust, &c. The forms of these are seldom alike in two -different kinds of insects, so that there is here a wide field for the -student. The dissection, moreover, is very easy, as they may be cut -from the body with a sharp knife or scissors, and mounted in balsam or -fluid. Many of the larvæ afford good specimens, as do also some of the -common Coleopterous insects. - -TONGUES, OR PALATES, OF MOLLUSCS.--Of the nature of these, Dr. -Carpenter gives the following description:--“The organ which is -commonly known under this designation is one of a very singular nature; -and we should be altogether wrong in conceiving of it as having any -likeness to that on which our ordinary ideas of such an organ are -founded. For, instead of being a projecting body, lying in the cavity -of the mouth, it is a tube that passes backwards and downwards beneath -the mouth, its higher end being closed, whilst in front it opens -obliquely upon the floor of the mouth, being, as it were, slit up and -spread out so as to form a nearly flat surface. On the interior of -the tube, as well as on the flat expansion of it, we find numerous -transverse rows of minute teeth, which are set upon flattened plates; -each principal tooth sometimes having a basal plate of its own, whilst -in other instances one plate carries several teeth.” These palates, or -tongues, differ much amongst the Gasteropods in form and size, some -of them being comparatively of an immense length. Many are amongst -the most beautiful objects when examined with polarized light. They -must, however, be procured by dissection, which is usually performed -as follows:--The animal is placed on the cork in the dissecting-trough -before mentioned, and the head and forepart cut open, spread out, -and firmly pinned down. With the aid of fine scissors or knife, the -tongue must be then detached from its fastenings, and placed in water -for a day or two, when all foreign matter may with a little care be -removed. In what way it should be mounted will depend on the purpose -for which it is intended. If for examination as an ordinary object, it -may be laid upon the slide and allowed to dry, which arrangement will -show the teeth very well. If we wish to see it as it is naturally, it -must be mounted in a cell with Goadby’s fluid; but if it is wanted as -a polarizing object, it must be floated upon a slide, allowed to dry -thoroughly, and then Canada balsam added in the usual manner. - -In the stomach, also, of some of these molluscs teeth are found, which -are very interesting objects to examine, and must be dissected out in -the same manner as the “tongues.” - -Since writing the above. Dr. Alcock (whose very beautiful specimens -prove him to be a great authority in this branch) has published some -of his experience in the second volume of the third series of “Memoirs -of the Literary and Philosophical Society of Manchester.” By his -permission I make the following extract:-- - -“This closes my present communication on the tongues of mollusca; but -as some members may possibly feel inclined to enter upon the inquiry -themselves, I think it will not be amiss to add a few remarks on the -manner in which they are to be obtained. - -“First, as to the kinds best worth the trouble of preparation. Whelks, -Limpets, and Trochuses should be taken first. Land and fresh-water -snails can scarcely be recommended, except as a special study,--their -tongues being rather more difficult to find, and the teeth so small -that they require a high power to show them properly. It would appear, -from Spallanzani’s description of the anatomy of the head of the snail, -that even he did not make out this part, although, in his curious -observations on the reproduction of lost parts, he must have carefully -dissected more snails than any other man. - -“As to preserving the animals till wanted, they should simply be -dropped alive into glycerine or alcohol. Glycerine is perhaps best -where only the tongues are wanted; but it leaves the animals very soft; -and as it does not harden their mucus at all, they are very slippery -and difficult to work upon when so preserved. - -“Then as to the apparatus required for dissection. In the first -place, all the work is to be done under water, and a common saucer is -generally the most convenient vessel to use. No kind of fastening down -or pinning out of the animal is needed; and, in fact, it is much better -to have it quite free, that you may turn it about any way you wish. -The necessary instruments are a needle-point, a pair of fine-pointed -scissors, and small forceps; the forceps should have their points -slightly turned in towards each other. - -“A word or two on the lingual apparatus generally, and on its special -characters in a few different animals, will conclude what I have to say. - -“The mode of using the tongue can be easily seen in any of the common -water-snails, when they are crawling on the glass sides of an aquarium; -it may then be observed that from between the fleshy lips a thick -mass is protruded, with a motion forwards and upwards, and afterwards -withdrawn, these movements being almost continually repeated. The -action has the appearance of licking; but when the light falls suitably -on the protruded structure, it is seen to be armed with a number of -bright points, which are the lingual teeth, so arranged as to give the -organ the character and action of a rasp. - -“If you proceed to dissection, and open the head of one of these -mollusca (say, for instance, a common limpet), you will find the cavity -of the mouth almost filled with the thick fleshy mass, the front of -which is protruded in the act of feeding; and on its upper surface, -extending along the middle line from back to front, is seen the strong -membranous band upon which the teeth are set. The mass itself consists -of a cartilaginous frame, surrounded by strong muscles; and these -structures constitute the whole of the active part of the lingual -apparatus.... - -“But the peculiarity of the toothed membrane, which makes its name of -‘_ribbon_’ so appropriate, is, that there is always a considerable -length of it behind the mouth, perfectly formed, and ready to come -forward and supply the place of that at the front, which is continually -wearing away by use. - -“In the limpet this reserve-ribbon is of great length, being nearly -twice as long as the body, and the whole of it is exposed to view on -simply removing the foot of the animal; nothing, then, can be easier -than to extract the tongue of the common limpet. But, unfortunately, -what you find in one kind of mollusc is not at all what you find in -another. In the Acmæas, for instance, which are very closely related -to the limpets, and have shells which cannot be distinguished, the -reserve portion of the ribbon has to be dug out from the substance -of the liver, in which it is imbedded, that organ being, as it were, -stitched completely through by a long loop of it.... It might be -thought a comfortable reflection that, at all events, one end of the -ribbon can always be found in the mouth; but in many cases this is -about the worst place to look for it. Perhaps it may appear strange -that in some of the smaller species, with a retractile trunk, a -beginner may very likely fail altogether in his attempt to find the -mouth; if, however, the skin of the back is removed, commencing just -behind the tentacles, there will be very little difficulty in making -out the trunk, which either contains the whole of the ribbon, as in -the whelk, or the front part of it, as in _Purpura_ and _Murex_, where -a free coil is also seen to hang from its hinder extremity.... In the -periwinkles the same plan of proceeding, by at once opening the back of -the animal, is best; and on doing so, the long ribbon, coiled up like a -watch-spring, cannot fail to be found. - -“In the Trochuses, and indeed in all the _Scutibranchiata_, one point -of the scissors should be introduced into the mouth of the animal, and -an incision made directly backwards in the middle line above to some -distance behind the tentacles; the tongue is then immediately brought -into view, lying along the floor of the mouth.” - -Dr. Alcock’s method of dissection will be found to differ in some -degree from the general rules before given; and when the tongue is -dissected out he washes it for one hour (shaking it now and then) in a -weak solution of potash. After cleaning thoroughly in water, it must be -mounted by one of the methods before mentioned. - -Amongst insects, especially the grasshopper tribe, are found many which -possess a gizzard, armed with strong teeth, somewhat similar to those -of the molluscs. It requires great nicety of manipulation to obtain -these for the microscope; but it would be useless to attempt any -description of the process here, as the strident can only be successful -by experience in dissecting objects less difficult to manage, and by -using the most delicate instruments. - -We have now considered most of those objects which require any -_peculiar_ treatment in section-cutting, &c.; but in no branch of -microscopic manipulation is experience more necessary than in this. - - - - -CHAPTER VI. - -INJECTION. - - -1. Injection is the filling of the arteries, veins, or other vessels -of animals with some coloured substance, in order that their natural -arrangement may be made visible. This is, of course, a delicate -operation, and needs special apparatus, which I will now attempt to -describe. - -2. _Syringe._--This is usually made to contain about two ounces. -On each side of the part next to the handle is a ring, so that the -finger may be thrust through it, and the thumb may work the piston -as in an ordinary syringe. The plug of the piston must be “packed” -with wash-leather, and fit so closely as to be perfectly air-tight; -and if, when it has been used awhile, it is found that some of the -liquid escapes past the plug into the back part of the body, it must -be _repacked_, which operation will be best understood by examining -the part. These syringes are made of various sizes, but in ordinary -operations the above will be all that is needed. The _nozzle_ is about -an inch long, and polished so accurately that there is no escape when -the _pipes_ are tightly placed upon it _dry_. - -3. The _pipes_ are usually about an inch long, to the end of which are -affixed thicker tubes so as to fit the nozzle, as before mentioned, -whilst a short arm projects from each side of these, so that the silk -or thread which is used to tie this artery, &c., upon the thin pipe may -be carried round these arms, and all danger of slipping off prevented. -The _pipes_ are made of different sizes, from that which will admit -only a very fine needle (and this will need now and then to be cleaned, -or to be freed from any chance obstruction), to that which will take a -large pin. These sizes must always be at hand, as the vessels of some -subjects are exceedingly minute. - -4. _Stopcock._--This is a short pipe like a small _straight_ tap, -which fits accurately upon the end of the syringe like the pipes, and -also takes the pipes in the same manner. The use of this is absolutely -necessary when the object is so large that one syringe full of liquid -will not fill it. If no preventive were used, some part of the liquid -would return whilst the syringe was being replenished, but the -stopcock is then turned as in an ordinary tap, and all danger of this -effectually removed. - -5. _Curved needles._--These are easily made by heating common needles -at the end where the eye is situated, and bending them with a small -pair of “pliers” into a segment of a circle half an inch in diameter. -They are, perhaps, more convenient when the bent part is thrown -slightly back where it commences. The pointed end is then thrust into -a common penholder, and the needle needs no re-tempering, as the work -for which it is wanted is simply to convey the thread or silk _under_ -any artery or vessel where it would be impossible to reach with the -unassisted fingers. - -6. A kind of _forceps_, commonly know by the name of “bullnose -forceps,” will be constantly required during the process of injecting. -These are short, usually very strong, but not heavy, and close very -tightly by their own spring, which may be easily overcome and so -released by the pressure of the fingers. When any vessel has not been -tied by the operator, and he finds the injected fluid escaping, one -of these “bulldogs” may be taken up and closed upon the opening. This -will cause very little interruption, and the stoppage will be almost as -effectual as if it were tied. - -7. When the ordinary mode of injection is employed, it is necessary -that the preparations be kept warm during the time they are used, -otherwise the gelatine or size which they contain becomes stiff, and -will not allow of being worked by the syringe. For this purpose we -must procure small earthenware or tin pots of the size required, which -will differ according to the kind of work to be done; and to each of -these a loose lid should be adapted to protect it from dust, &c. These -pots must be allowed to stand in a tin bath of water, under which a -lamp or gas flame may be placed to keep the temperature sufficiently -high to insure the perfect fluidity of the mixture. The tin bath is, -perhaps, most convenient when made like a small shallow cistern; but -some close it on the top to place the pots upon it, and alter the shape -to their own convenience. - -8. We will now inquire into some of the materials which are needed in -this operation; the first of which is _size_. This substance is often -used in the form of _glue_, but it must be of the very best and most -transparent kind. To make the liquid which is to receive the colours -for the usual mode of injecting, take of this glue seven ounces, and -pour upon it one quart of clean water; allow this to stand a few hours, -and then boil gently until it is thoroughly dissolved, stirring with a -wooden or glass rod during the process. Take all impurities from the -surface, and strain through flannel or other fine medium. The weather -affects this a little as to its stiffness when cold, but this must be -counteracted by adding a little more glue if found too liquid. - -9. Instead of glue, gelatine is generally used, especially when the -work to be accomplished is of the finer kind. The proportions are very -different in this case, one ounce of gelatine to about fourteen ounces -of water being sufficient. This, like glue, must be soaked a few hours -in a small part of the cold water, the remainder being boiled and -added, when it must be stirred until dissolved. A good size may be made -by boiling clean strips of parchment for awhile, and then straining -the liquid whilst hot through flannel; but when the injections are -to be _transparent_, it is of the greatest importance that the size -be as colourless as possible. For this purpose good gelatine must be -employed, as Nelson’s or Cox’s: some persons of experience prefer the -latter. - -10. _Colours._--The size-solution above mentioned will need some -colouring matter to render it visible when injected into the vessels -of any animal, and different colours are used when two or more kinds -of vessels are so treated, in order that each “set” may be easily -distinguished by sight. The proportion in which these colours are added -to the size-solution may be given as follows:-- - -11. For-- - - Red 8 parts of size-solution - (by weight) to 1 part of vermilion. - Yellow 6 ” ” 1 ” chrome yellow. - White 5 ” ” 1 ” flake-white. - Blue 3 ” ” 1 ” blue-smalt, fine. - Black 12 ” ” 1 ” lamp-black. - -Whichever of these colours is made use of must be levigated in a mortar -with the addition of a very small quantity of water until every lump -of colour or foreign matter is reduced to the finest state possible, -otherwise in the process of injecting it will most likely be found -that some of the small channels have been closed and the progress -of the liquid stopped. When this fineness of particles is attained, -warmth sufficient to render the size quite fluid must be used, and the -colour added gradually, stirring all the time with a rod. It may be -here mentioned that where one colour only is required, vermilion is, -perhaps, the best; and blue is seldom used for opaque objects, as it -reflects very little more light than black. - -12. When it is wished to fill the capillaries (the minute vessels -connecting the arteries with the veins), the “Micrographic Dictionary” -recommends the colouring matter to be made by double decomposition. As -a professed handbook would be, perhaps, deemed incomplete without some -directions as to the mode of getting these colours, I will here make -use of those given in that work. For red, however, vermilion, as above -stated, may be used; but it must be carefully examined by reflected -light to see whether it be free from all colourless crystals or not. -It must first be worked in a mortar, and then the whole thrown into a -quantity of water and stirred about; after leaving it not longer than -a quarter of a minute, the larger portions will settle to the bottom, -and the liquid being poured off will contain the finer powder. This may -then be dried slowly, or added to the size whilst wet in the manner -before advised. - -13. _Yellow injection._--To prepare this, take-- - - Acetate (sugar) of lead 380 grains. - Bichromate of potash 152 ” - Size 8 ounces. - -Dissolve the lead salt in the warm size, then add the bichromate of -potash finely powdered. - -Some of the chromic acid remains free, and is wasted in this solution, -so the following is given:-- - - Acetate of lead 190 grains. - Chromate of potash (neutral) 100 ” - Size 4 ounces. - -The first of these has the deepest colour, and is the most generally -used. - -14. _White injection._--This is a carbonate of lead:-- - - Acetate of lead 190 grains. - Carbonate of potash 83 ” - Size 4 ounces. - -Dissolve the acetate of lead in the warm size, and filter through -flannel; dissolve the carbonate of potash in the smallest quantity of -water, and add to the size: 143 grains of carbonate of soda may be -substituted for the carbonate of potash. - -15. For blue injection, which is not, however, much used with reflected -light, as before stated, take-- - - Prussian blue 73 grains. - Oxalic acid 73 ” - Size 4 ounces. - -The oxalic acid is first finely powdered in a mortar, the Prussian blue -and a little water added, and the whole then thoroughly mixed with the -size. - -16. It may here be repeated, that it is only when the capillaries are -to be filled that there is any need to be at the trouble to prepare -the colours by this double decomposition; and, indeed, colours ground -so finely may be procured that the above instructions would have been -omitted, had it not been supposed that some students might find a -double pleasure in performing as much of the work as possible by their -own unaided labours. - -17. The process of injection may now be considered; but it is -impossible for written instructions to supply the place of experience. -I will do my best, however, to set the novice at least in the right -way. There are two kinds of injection--one where the object and colours -are opaque, and consequently fit for examination by _reflected_ light -only; the other, where the vessels are filled with transparent colours, -and must be viewed by _transmitted_ light. The first of these is most -frequently employed, so we will begin with it. In the object which -is to be injected a vessel of the kind which we wish to be filled -must be found; an opening must then be made in it to allow one of the -small pipes before mentioned to be thrust some distance within it. -When this is accomplished, thread the curved needle with a piece of -silk thread, or very fine string, which some operators rub well with -beeswax. This thread must not be too thin, else there is danger of -cutting the vessel. The cord is then carried under the inserted pipe, -and the vessel bound tightly upon it, the ends being brought up round -the transverse arms, and there tied; so that all danger of accidentally -withdrawing the pipe is obviated. Care must now be used in closing -all the vessels which communicate with that where the pipe is placed -lest the injecting fluid escape; and this must be done by tieing them -with silk. Should, however, any of these be left open by accident, the -bullnose forceps must be made use of, as before recommended. - -18. The part to be injected must now be immersed in warm water, -not, however, above 100° Fahrenheit, and be left until the whole is -thoroughly warmed. Whilst this is being done, the coloured size must -be made ready by the pot being placed in the tin bath of warm water, -which must be of sufficient temperature (about 110° Fahrenheit) to -keep it perfectly liquid. For the same purpose, the syringe is often -tightly covered with two or three folds of flannel; and, indeed, -there is no part of the process which requires more attention. If the -substance to be injected is too hot, it is injured; whilst, if any of -the articles are too cold, the gelatine, or size, loses a part of its -fluidity, and consequently cannot enter the minute parts. When all is -prepared, the syringe, with the stopcock attached, should be warmed, -and then filled and emptied with the injecting fluid two or three -times, care being taken that the end of the syringe be kept beneath any -bubbles which form upon the surface. The syringe may then be filled, -and closely attached to the pipe which is tied in the vessel. With a -firm and steady pressure the piston must be forced downwards, when the -substance will be perceived to swell, and the colour show itself in -places where the covering is thin. When the syringe is _almost_ emptied -of its contents, the stopcock must be turned to prevent any escape -of the injection from the subject. It must then be refilled, as in -the first instance, and the process repeated. I say _almost emptied_, -because it is well not to force the piston of the syringe quite to the -bottom, lest the small quantity of air which frequently remains be -driven into some of the vessels, and the object be injured or quite -ruined. As the injection is proceeded with, it will be found that the -force required grows greater, yet care must be taken not to use too -much, or the vessels will burst, and render all the labour fruitless. -The movement of the piston must be occasionally so slow as to be almost -imperceptible, and for this reason it is sometimes marked with lines -about one-eighth of an inch apart. - -19. Of course, during the whole process the injecting fluid and subject -must be kept at a temperature high enough to allow the liquid to flow -freely; and the escape of a little of it need cause no fears to the -student, as it is almost impossible to fill any subject without some -loss. When the injected object has received sufficient fluid, it should -have a plump appearance, owing to all the vessels being well filled. -The vessel must then be tied up where the pipe was inserted, and the -whole left in cold water two or three hours, after which time it may be -mounted; but it may be well to notice a few things which the beginner -ought to know before entering into that part of the process; and he -may be here informed that it is not necessary to mount the objects -immediately, otherwise it would be impossible for one person to make -use of half of any large subject, as it would be in a state of decay -long before each part could have been examined and separated. Large -pieces should be therefore immersed in equal parts of spirits of wine -and water, or glycerine, which some think better still, and thus -preserved in bottles until time can be given to a closer examination. - -20. In operating upon large subjects, entire animals, &c., the constant -pressure required by the piston of the syringe grows wearisome, besides -occupying both hands, which is sometimes inconvenient when working -without assistance. To obviate this, another way of driving the syringe -was published in the “Micrographic Dictionary” which I will quote -here:--“We have therefore contrived a very simple piece of apparatus, -which any one can prepare for himself, and which effects the object -by mechanical means. It consists of a rectangular piece of board, two -feet long and ten inches wide, to one end of which is fastened an -inclined piece of wood (equal in width to the long board, and one foot -high). The inclined portion is pierced with three holes, one above the -other, into either of which the syringe may be placed--the uppermost -being used for the larger, the lowermost for the smaller syringe; and -these holes are of such size as freely to admit the syringe covered -with flannel, but not to allow the rings to pass through them. The -lower part of the syringe is supported upon a semiannular piece of -wood, fastened to the upper end of an upright rod, which slides in -a hollow cylinder fixed at its base to a small rectangular piece of -wood; and by means of a horizontal wooden screw, the rod may be made to -support the syringe at any height required. The handle of the syringe -is let into a groove in a stout wooden rod connected by means of two -catgut strings with a smaller rod, to the middle of which is fastened -a string playing over a pulley, and at the end of which is a hook for -supporting weights, the catgut strings passing through a longitudinal -slit in the inclined piece of wood.” When in use the syringe is filled -with injecting fluid, and passed through one of the three holes which -is most suitable. The object being placed so that the pipe and syringe -can be best joined, the rod and strings are set in order, and a weight -placed on the hook. The stopcock must then be opened gradually, when -the operator will be able to judge whether the weight is a proper one -or not: if the piston is driven with any speed, there is danger of -injuring the subject, and less weight may be used; if, however, the -piston does not move, more must be added. - -21. Such is the method recommended by the “Micrographic Dictionary,” -and perhaps it is as good as any mechanical plan could be; but where -the operator is willing to undergo the labour of performing all this -with the hand, he has a much better chance of succeeding, because the -pressure can be regulated so accurately, and changed so quickly when -requisite, that no mere machine can compete with it, however well -contrived. - -22. When the beginner attempts to inject a subject, one of his -difficulties is finding the vessel from which to commence. Another -consists in distinguishing the arteries from the veins; but this is -partly removed by making a longitudinal incision in the vessel, and -with a blunt thick needle probing a little distance into the tube. The -artery will be found thicker in the coating than the vein, and the -difference is easily perceived by this mode of testing: the vein is -also of a bluer colour than the artery. I say above, a “longitudinal -incision” must be made: the reason for this is, the artery when cut -across contracts considerably, and is lost in the adjoining substance; -but where the opening is made _longitudinally_ all danger of this -contraction is obviated. - -23. The different systems of vessels are often injected with various -colours, so that their relative positions, &c., may be shown most -clearly. In some specimens, the veins are injected with white, and the -arteries with red; in the kidney, the urinary tubes are often filled -with white, and the arteries with red. Then, again, the liver affords -tubes for three or four colours. But no written instructions on this -point can benefit the young student, and he must be content for a -while to employ himself with single colours until he has gained the -mechanical skill and the primary knowledge which are necessary before -he can make any advance. - -24. We will now consider the best methods of _mounting_ injected -objects. They must always be well washed in water after they have been -kept in any preservative liquid, using a camel-hair pencil to clean the -surface if necessary. Many parts when injected are in masses, such as -the lungs, liver, &c., of animals, and consequently sections of these -must be cut. For this purpose Valentine’s knife is very convenient, -as the thickness can be regulated so easily; but where the injections -are opaque, there is no need to have the sections very thin. Some few -of this kind undergo comparatively little change in drying, so that -the section may be well washed and floated upon the glass slide in the -place desired, where it will dry perfectly and adhere to it. It must -be then moistened with turpentine and mounted in Canada balsam like -other objects. No great heat should be used with these preparations, -as it is very liable to injure them; and some of the colours seem to -suffer a slight contraction when any great degree of warmth is applied. -There are many objects, however, which must be seen in the mass to be -understood, and, indeed, lose all their form and beauty in drying, such -as certain parts of the intestines, &c. These must be mounted in fluid, -with the precautions noticed at length in Chapter IV., and for this -purpose either Goadby’s fluid, the chloride of zinc solution, or spirit -diluted with ten parts of distilled water, may be employed. It is a -good thing, when practicable, to mount similar objects on two separate -slides, using different preservative liquids, and taking the precaution -of marking each with the kind of liquid employed. This not only serves -as a guide to what is best for certain subjects, but if one is injured, -there will probably be a good specimen in the other. - -25. It may be here mentioned that many are now mounting sections of -injected substances with the balsam and chloroform before mentioned, -instead of using balsam alone, and consider that the labour is much -lessened thereby. - -26. A description of that mode of injection which is most generally -employed has now been given, but this is not the only method of -effecting our object. A most ingenious process was invented by M. -Doyers, requiring no artificial warmth, by which many beautiful objects -have been prepared. Make a solution of bichromate of potash, 524 grains -to a pint of water, and throw this into the vessels to be injected; -then take 1,000 grains of acetate of lead dissolved in half a pint -of water, and force this into the same vessels. A decomposition now -takes place in the vessels, and the yellow chromate of lead is formed. -In this decomposition, however, the acetate of potash also is formed -and as this salt has an injurious action upon the cells, Dr. Goadby -recommends nitrate of lead to be used, which preserves rather than -destroys them. He also advises the addition of two ounces of gelatine -dissolved in eight ounces of water, to eight ounces of the saturated -solution of each salt; but with this addition the hot-water bath would -be required to keep the injecting fluid liquid. - -27. Many of these are best mounted in balsam, in the same manner as -those made in the ordinary way; whilst others are best shown when -preserved in liquids, for which purpose Goadby’s fluid may be employed. - -28. This mode of making injections with chromate of lead is deemed by -many the best, especially where one colour only is employed. But it -must be allowed that there is a little more danger of failure where two -separate fluids are used for the same vessels. - -29. We will now consider the best manner of making _transparent_ -injections, which, for many purposes, possess an undoubted advantage -over the opaque ones. But it must be remembered that there are certain -subjects to which no transparent injection could be applied, as they -are too thick when in their natural state, and cutting would destroy -all that beauty which is shown by the different parts in their -relative adaptation. For those objects, however, which must be cut -into sections to display their wonders, or are naturally thin--such -as some of the finer tissues, livers, kidneys, &c.--transparency is a -great acquisition, and enables us to understand the arrangement of the -vessels more perfectly. Again, another advantage is the simplicity of -the process; no hot water is needed with some preparations, either for -the subject or the injecting fluid, which runs into the minute vessels -thoroughly and easily, whilst the cost is small. - -30. For this kind of injection no colour is so commonly made use of -as Prussian blue. It is not a good one, as was before stated, for -any opaque object, as the light reflected from it appears almost -black; yet by transmitted light no colour is more useful, because -its distinctness is equally great by artificial light and ordinary -daylight. The method of preparing this, as given by Dr. Beale, is as -follows:-- - - Glycerine 1 ounce. - Wood naphtha, or pyroacetic acid 1½ drachm. - Spirits of wine 1 ounce. - Ferrocyanide (yellow prussiate) of potash 12 grains. - Tincture of sesquichloride of iron 1 drachm. - Water 4 ounces. - -Dissolve the ferrocyanide of potash in one ounce of the water; -add the tincture of sesquichloride of iron to another ounce. Mix -these solutions gradually together, shaking the bottle well which -contains them--it is best to add the iron to the potash solution. -When thoroughly mixed, these solutions should produce a dark-blue -mixture, perfectly free from any perceptible masses or flocculi. Next -mix the naphtha and spirits of wine, and add the glycerine and the -remaining two ounces of water. This must now be slowly mixed with the -blue liquid, shaking the whole well in a large bottle whilst the two -come together. The tincture of sesquichloride of iron is recommended, -because it can always be obtained of a uniform strength. - -31. Dr. Turnbull used a mixture slightly different from the above, -which is made with the sulphate of iron:-- - - Purified sulphate of iron 10 grains. - Ferrocyanide of potassium 32 grains. - Glycerine 1 ounce. - Pyroacetic acid 1½ drachm. - Alcohol 1 ounce. - Water 4 ounces. - -Dissolve the sulphate of iron in one ounce of the water, gradually add -the ferrocyanide of potassium dissolved in another ounce, and proceed -as above. - -32. Dr. Beale also gives us the following carmine injection to be -employed in the same way as the blue.[G] Take-- - - Carmine 5 grains. - Glycerine, with 8 or 10 drops of hydrochloric acid ½ ounce. - Glycerine (pure) 1 ounce. - Alcohol 2 drachms. - Water 6 drachms. - -Mix the carmine with a few drops of water, and when well incorporated -add about five drops of liquor ammoniæ. To this dark-red solution about -half an ounce of the glycerine is to be added, and the whole well -shaken in a bottle. Next, very gradually pour in the acid glycerine, -frequently shaking the bottle during admixture. Test the mixture with -blue litmus-paper, and if not of a very decidedly acid reaction, a few -more drops of acid may be added to the remainder of the glycerine and -mixed as before. Lastly, mix the alcohol and water very gradually, -shaking the bottle thoroughly after adding each successive portion -till the whole is mixed. This fluid may be kept ready prepared, and -injections made very rapidly with it. - - [G] When, however, it is desirable to cut very thin sections of - the injected subject, the carmine is sometimes added to a - solution of fine gelatine--gelatine one part to water eight - parts. But the warm water and mode of proceeding which - are used with the size solutions before described will be - necessary in this case also. - -33. The method of making injections with these colours is the same as -with the gelatine mixtures before described, except that no heat is -required, and consequently most of the trouble removed. The bottle of -the fluid must be well shaken immediately before use; and when the -object is injected, we must allow it to remain in a cool place for a -few hours before cutting it. Thin sections of the subject may be cut -with Valentine’s knife, as before described, and are very beautiful -transparent objects. Some of the finer tissues, also, are shown much -better by this mode of injection than by the opaque, and are easily -mounted by washing in clean water when first separated, and floating -upon a slide, where they must be allowed to dry thoroughly. They may -then be immediately mounted in balsam, or kept in the dry state until -it is convenient to finish them; but in many cases this keeping, if too -much prolonged, will injure the object. If it is desired to transfer -the section to another slide, it will be necessary to wet it thoroughly -with water by the aid of a camel-hair pencil, and then gently strip it -off with the forceps. When it is wished to preserve injected subjects -in “masses,” it must be done by immersion in spirit, and the sections -may be cut at leisure. Most of these transparent objects may be mounted -in Canada balsam; but some recommend glycerine or glycerine jelly, as -allowing the use of a higher power in their examination, and preserving -them in a more natural form. - -34. A few subjects may be noticed which are very beautiful when -injected, and amongst these are the eyes of many animals. They -must be injected by the artery in the back part, and when the blue -transparent liquid is employed, nothing can exceed the delicate beauty -which some of the membrane bears. It must, however, be dissected with -care, but well repays us for the trouble. Water-newts and frogs are -not difficult subjects, and in their skin and other parts are many -interesting objects. Amongst the commoner animals--rats, rabbits, cats, -&c. &c.--almost endless employment may be found, making use either of -portions or the whole animal at once. The intestines of many of these -are very beautiful. We must divide them with a pair of scissors along -the tube, and cleanse them from all the matter; the coating may then be -laid upon a slide, and any remaining impurity removed with a camel-hair -pencil and water. When dried it may be mounted in balsam, and having -been injected with the transparent blue, its minute beauty is shown -most perfectly. In injecting a sheep’s foot, which is a good object, -the liquid should be forced into it until a slight paring of the hoof -shows the colour in the fine channels there. - -35. When the lungs of small animals are injected, the finest fluid must -be used, as some of the capillaries are so small that it is not an easy -matter to fill them properly. And before entering upon these subjects, -a certain proficiency in the mode of using the syringe, &c., should be -obtained by practising upon simpler parts. - -36. No subjects are more difficult to inject than fish, owing to the -extreme softness of their tissues. Dr. Hogg recommends the tail of the -fish to be cut off, and the pipe to be put into the divided vessel -which lies just beneath the spinal column; by which method beautiful -injections may be made. The gills, however, are the most interesting -part as microscopic objects. - -37. These instructions may seem very imperfect to those who have had -much experience in this branch; but they will remember that their -own knowledge was not gained from any written descriptions, but was -forced upon them by frequent failures, some of which probably were -very disheartening. As I before stated, it is very difficult (if not -impossible) to accomplish much without some knowledge of anatomy. - -38. I may here mention that the transparent injections sent over from -the Continent are beautifully executed by Hyrtl of Vienna (who states -that the injected fluid is composed of gelatine and carmine), Dr. -Oschatz of Berlin, the Microscopic Institute of Wabern, Schaffer and -Co. of Magdeburg, and others. Some of these will bear examining with a -high power. A friend informs me that he measured a vessel in a rat’s -tongue by Hyrtl, which was 1-7200th of an inch in diameter, and had -a clear outline with quarter-inch objective. He has also made many -experiments with the same materials, but has as yet failed in producing -perfectly distinct outlines, there being a tendency of the colouring -matter (magenta, carmine. &c.) to diffuse itself through the coats of -the vessels into the surrounding tissues, although he has varied the -pressure from one half a pound to sixty pounds. He believes the vessels -are first washed out (injected with warm water and pressure applied), -then some fluid introduced which renders the arteries impervious to the -coloured fluid afterwards injected. - -39. He finds that after washing out the vessels as above, the injecting -fluid is much more easily introduced. He has used a strong solution -of gallic acid previously to injecting with the colouring matter -(in one experiment only), and the result was satisfactory. He puts -the query,--Might not carbolic acid have a similar effect? He has -often used it with injections to preserve the specimens, but not in -sufficient quantity to act in the way indicated above. - -Since writing the above, Mr. J. G. Dale, F.C.S., and I have made -numerous experiments with carmine injection, and have at length -been favoured with what we deem success. Some of the vessels in a -kitten lately injected do not exceed 1-2000th of an inch in diameter, -and present a clear outline with one-fifth objective. There is no -extra-vasation, neither does the colouring matter show any grain except -when a very high power is employed. The following is our process:-- - - Take 180 grains best carmine. - ½ fluid ounce of ammonia, commercial strength, viz., - 0·92, or 15° ammonia meter. - 3 or 4 ounces distilled water. - -Put these into a small flask, and allow them to digest without -heat from twenty-four to thirty-six hours, or until the carmine is -dissolved. Then take a Winchester quart bottle, and with a diamond mark -the spot to which sixteen ounces of water extend. The coloured solution -must be filtered into the bottle, and to this pure water should be -added until the whole is equal to sixteen ounces. - -Dissolve 600 grains potash alum in ten fluid ounces of water, and add -to this, under constant boiling, a solution of carbonate of soda until -a slight permanent precipitate is produced. Filter and add water up -to sixteen ounces. Boil and add the solution to the cold ammoniacal -solution of carmine in the Winchester quart, and shake vigorously for -a few minutes. A drop of this placed upon white filtering-paper should -show no coloured ring. If much colour is in solution the whole must -be rejected, because, although it is possible to precipitate all the -colouring matter by the addition of ammonia or alum, it is not well to -do so, as the physical condition of the precipitate is thereby altered. - -Supposing the precipitation to be complete, or very nearly so, shake -vigorously for at least half an hour, and allow it to stand until quite -cold. The shaking must then be renewed for some time, and the bottle -filled up with pure water. - -After allowing the precipitate to settle a day, draw off the clear -supernatant fluid with a syphon. Repeat the washing until the clear -liquid gives little or no precipitate with chloride of barium. So much -water must be left with the colour at last that it shall measure forty -fluid ounces. - -For the injecting fluid take twenty-four ounces of the above coloured -liquid, and three ounces of good gelatine. Allow these to remain -together twelve hours, and then dissolve by the heat of a water bath; -after which it should be strained through fine muslin. - -As this injecting fluid contains gelatine, the hot water, and other -contrivances mentioned in a former part of the chapter, will be -necessary here also, but no peculiar treatment will be required. - - - - -CHAPTER VII. - -MISCELLANEOUS. - - -It must be evident to all readers that there are various objects -of interest to the microscopist which cannot be properly placed -amongst any of the forementioned classes, but must not be omitted in -such a guide as this professes to be. Of these may be mentioned the -circulation of the blood in various animals, the rotary motion of the -fluid in many plants, the best means of taking minute photographs, &c. -&c. - -Perhaps the most interesting of these objects is the circulation of -the blood through the finer vessels of various parts of the animals -made use of for these purposes, which parts, it is evident, must be -very transparent to afford a perfect view of this phenomenon. The -web of the frog’s foot is very frequently made use of, but requires -a certain arrangement, which we will now describe. A piece of thin -wood (Dr. Carpenter recommends _cork_) is taken, about eight inches -long and three wide; about an inch from one end is cut a hole, half or -three-quarters of an inch in diameter. The body of the frog is then -placed in a wet bag, or wrapped in wet calico, whilst the hind-foot -projects; the whole is then laid upon the piece of wood so that the -foot, which is left free, may be extended over the hole. The web must -then be spread out, and secured either by threads to small pins on -the wood, or the pins must be driven through the web into the wood, -and so kept in position. A few bands of tape must be passed round the -body, the leg, and the wood, to prevent any disarrangement arising from -the animal starting, &c. Care must be taken that the tape is not too -tight, else the circulation will be very slow or altogether stopped. -The wood must now be fixed upon the stage, with the aperture under -the object-glass: this is sometimes done by simply binding it, or a -spring is fixed so as to accomplish the same object without so much -trouble. With a half-inch power the blood may now be seen to flow very -distinctly. The frog may be used for hours if care is taken to prevent -the web from becoming dry, by wetting it with a little water from time -to time. The piece of wood or cork upon which the frog is laid is -often made to give place to the “frog-plates,” supplied by opticians. -These are made of brass, somewhat resembling the piece of wood above -recommended, but each maker’s pattern differs according to his own -taste. - -The tongue of the frog is also sometimes used for the purpose of -showing the circulation of the blood, which is done in the following -manner:--The body is wrapped with the calico, and made fast to the -plate as before, only the _mouth_ of the frog is brought to the -opening. The tongue is then gently drawn out of the mouth and pinned -down over the aperture, when the circulation will be well shown. But, -as Dr. Carpenter observes, the cruelty of this mode of treatment is so -repulsive that it is unjustifiable. - -Tadpoles of the frog (which, of course, are only obtainable in their -season) are good subjects for showing the circulation of the blood. -They are best suited for the microscope when about one inch long. The -tadpoles of the newt and toad also are equally suitable. They may -be placed in a very shallow glass trough with a little water, and a -narrow band of linen bound lightly round in some part not required for -examination, to keep them from moving; or they may be laid upon a glass -plate with a drop or two of water, and a thin glass covering lightly -bound upon it. Dr. Carpenter, however, places them first in cold water, -gradually adding warm until the whole becomes about 100°, when the -tadpole becomes rigid, whilst the circulation is still maintained. I -have not, however, found this necessary, the thin glass accomplishing -all that is desired. The tail is generally the most transparent, and -shows the circulation best; but in some of the newt larvæ the blood may -be traced down to the very extremities if they are not _too old_. Mr. -Whitney places the tadpole upon its back, by which means the heart and -other internal arrangements may be seen. - -Amongst fishes also may be found subjects for the same purpose, but -they seldom furnish as good examples as those before mentioned, because -the blood-vessels are not nearly so abundant, as in the foot of the -frog, &c. The stickleback is, however, procurable almost in any place -during the summer months, and may be laid in a shallow trough, loosely -bound down as the tadpole. The tail may be covered with a piece of thin -glass to prevent him curling it to the object-glass. The power needed -with this will be about the same as with the other subjects--viz., half -to quarter inch object-glass. - -It is not absolutely necessary to go to reptiles or fishes for this -curious sight, as some other animals serve very well. In the wings of -the common bat may be found a good subject. These must be stretched out -on something resembling the frog-plate before described, when those -parts near to the bones will show the _largest_ vessels very clearly. -The ear of a young mouse is an illustration of the same phenomenon, but -it is very difficult to fix it in a good position, as these animals are -so very timid and restless. - -Amongst insects also the same law may be observed, by placing them in -the “cage,” or “live-box,” so as to keep them still, but not to injure -them by too much pressure. In certain larvæ this is particularly well -shown, as that of the day-fly and plumed gnat; but in some of these -the blood is almost colourless. In the wings also of many insects this -circulation is well seen, as in those of the common housefly; but as -these parts become dry in a few days, the subject should not be more -than twenty-four hours old. - -Somewhat approximating to the forementioned phenomenon, is the -“rotation” of fluid in the cells, or, as it is usually termed, the -_circulation of the sap_, of plants. This is shown in certain vegetable -growths as a constant stream of thick fluid, wherein small globules -are seen; which stream flows round the individual cells, or up the -leaf, turning at the extremity, and down again by a different but -parallel channel. There is little or no difficulty in showing this in -many plants; but some are, of course, better than others, and require -a different treatment; we will, therefore, notice a few of these. -Perhaps the best of all is the _Vallisneria spiralis_, which is an -aquatic plant, frequently grown in, but not really belonging to, this -country. As it somewhat resembles grass, the leaf is not used in its -natural state, but a thin section cut lengthwise with a razor or other -sharp instrument--this section, however, is much better when the outer -surface has been first removed. It should then be laid upon a slide -with a drop or two of water, and covered with a piece of thin glass. -Often the cutting of the section seems to be such a shock to the leaf -that no motion is visible for awhile, but in a short time the warmth -of an ordinary sitting-room will revive it, and with a quarter-inch -object-glass the currents will be rendered beautifully distinct. -Where the “stream” is unusually obstinate the warmth may be slightly -increased, but too great heat destroys the movement altogether. In the -summer, any of the leaves show this “circulation” very well; but in the -winter, the slightly yellow ones are said to be the best. - -The Vallisneria requires to be cut in sections to show this -“circulation;” but there are many plants of which it is but necessary -to take a fragment and lay it upon a slide. The _Anacharis alsinastrum_ -is one of these: it grows in water, having three leaves round the -stem, then a bare portion, again another three leaves, and so on. One -of these leaves must be plucked close to the stem, and laid upon a -slide with a drop of water. Thin glass should be placed upon it, and -along the mid-rib of the leaves the “circulation” may be seen most -beautifully when a good specimen has been chosen; but it requires -rather more power than the Vallisneria. This plant is very common in -many parts of the country, a great number of our ponds and streams -being literally choked up by it. In the _Chara vulgaris_ and two or -three of the Nitellæ, &c., this phenomenon may also be seen with no -preparation except plucking a part from the stem and laying it upon a -slide as with the Anacharis. In using the Frog-bit, the outer part of -the young leaf-buds must be taken to obtain the best specimens for this -purpose; but a section of the stem will also show the “circulation,” -though not so well. The plants before mentioned are all aquatic, but -the same movement of the globules has been observed in several kinds -of land plants, as in the hairs upon the leaf-stalks of the common -groundsel; but these do not show it so well, nor are they so easily -managed as the above. - -Many microscopists who are not fortunate enough to be in the -neighbourhood of these plants (indeed the Vallisneria is a foreign one) -grow them in jars, so a few remarks as to the treatment they require -will not be out of place. The Vallisneria requires a temperature not -lower than 55° or 60°, and even a higher degree than this renders its -growth quicker; and no great change must take place: the more equable -the temperature the more healthy will the plant be. A glass jar should -be taken, having an inch or two of mould at the bottom, which must be -pressed down closely, and the plant must be set in this. Water must -then be gently poured in, so as not to disturb the mould. As this plant -flourishes best when the water is frequently changed, Mr. Quekett -recommends that the jar should be occasionally placed under a tap of -water, and a very gentle stream allowed to fall into it for several -hours, by which means much of the confervoid growth will be got rid of -and the plant invigorated. The Anacharis may be rooted in the earth -like the Vallisneria, but a small detached piece may be thrown into the -jar of water and there left until wanted. For months the “circulation” -will be well shown by it, and it will probably grow and increase. It -is also very healthy in an in-door aquarium. It is recommended that -the jars in which any of the _Chara_ are grown should be moved about -as little as possible, as the long roots are very tender, and will not -bear agitation. - -An object which is interesting to the microscopist, as well as the -unscientific observer, is the _growth_ of seeds, as it is often -erroneously termed. A shaving of the outside of the seed is taken and -laid upon the glass slide; a thin glass cover is then placed upon it, -and a drop of water applied to the edge of this. The water will then -gradually flow under the glass and reach the section of the seed, -when the transparent fibres will appear to spring out and “grow” for -some minutes. This, however, is produced by the unfolding of a spiral -formation in the cells, and, therefore, has really no similarity to the -true growth. The seeds of the Salvias, Collomias, Senecio, Ruellia, -&c., are well suited for the display of this curious sight. - -To watch the development of the spores of ferns, and the fertilization -and products, Dr. Carpenter recommends the following mode of -proceeding:--“Let a frond of a fern, whose fructification is mature, -be laid upon a piece of fine paper, with its spore-bearing surface -downwards; in the course of a day or two this paper will be found -to be covered with a very fine brownish dust, which consists of the -discharged spores. This must be carefully collected, and should be -spread upon the surface of a smoothed fragment of porous sandstone; -the stone being placed in a saucer, the bottom of which is covered -with water, and a glass ‘tumbler’ being inverted over it, the -requisite supply of moisture is insured, and the spores will germinate -luxuriantly. Some of the prothallia soon advance beyond the rest; -and at the time when the advanced ones have long ceased to produce -antheridia, and bear abundance of archegonia, those which have remained -behind in their growth are beginning to be covered with antheridia. -If the crop be now kept with little moisture for several weeks and -then suddenly watered, a large number of antheridia and archegonia -simultaneously open, and in a few hours afterwards the surface of -the larger prothallia will be found almost covered with moving -antherozoids. Such prothallia as exhibit freshly opened archegonia are -now to be held by one lobe between the forefinger and thumb of the -left hand, so that the upper surface of the prothallium lies upon the -thumb; and the thinnest possible sections are then to be made with a -narrow-bladed knife perpendicularly to the surface of the prothallium. -Of these sections, which after much practice may be made no more than -1-15th of a line of thickness, some will probably lay open the canals -of the archegonia, and within these, when examined with a power of 200 -or 300 diameters, antherozoids may be occasionally distinguished.” - -Another interesting object to the young microscopist is afforded by the -spores of the equiseta (or horsetails, as they are often called). These -may be obtained by shaking the higher portion of the stems when the -spores are ripe. They will then fall like small dust, and may be placed -under the microscope. The spores are then seen to consist of a somewhat -heart-shaped mass with bands rather intricately curled around it. As -they dry these bands expand, and are seen to be four lines at right -angles, with the ends clubbed, as it may be called. If, whilst watching -them, the spores are breathed upon, these bands immediately return to -their former state, and are closely curled around the spore; but as -they gradually dry again expand. This experiment may be repeated many -times, and is a very interesting one. - -The above are the principal objects which could not possibly be -included in any of the former chapters, but would have left a most -interesting branch untouched had it been neglected. There is another -subject also which should not be passed by--viz., the production of -minute pictures which serve as objects for microscopic examination. - -I may here mention that as this manual is simply to enable the -young student to prepare and mount his objects, the photography of -_magnified_ objects has evidently no place here. - -Few slides caused so much astonishment as these minute photographs when -first exhibited; small spots were seen to contain large pictures, and a -page of printed matter was compressed into the one-hundredth part of a -square inch. It would be impossible in this place to give the inquirer -any instruction in the manipulation of photography, so it must be -assumed that he already knows this. - -We will first consider the process performed by artificial light. The -collodion employed in photographing generally shows as much structure -when magnified as is found in linen of moderate texture; but this is -not always the case, as some samples bear much enlargement without any -of this appearance. It is evident that a structure so coarse would make -it entirely unfit for these minute pictures, as all the small markings -would be destroyed, or so interfered with that no great enlargement -would be practicable. To obtain almost structureless collodion is not -an easy matter, and a clever practitioner in this branch of photography -states that he knows of no method to accomplish this with certainty, -but he himself tries different samples until he falls upon a suitable -one, which he then lays aside for this object. A beneficial effect -is often derived from keeping the collodion awhile, but this is not -always the case. The slides should be chosen of an equal thickness, -so that when focussed upon one no re-adjustment may be necessary for -the others. The glass should, of course, be free from any roughness, -scratches, or other imperfections, and of first-rate quality and colour. - -The microscope must then be placed in a horizontal position, and the -eye-piece removed, the stage having a small clip upon it to keep the -prepared plate in position. The negative must then be supported at a -distance from the end of the microscope tube from which the eye-piece -was withdrawn. This distance will, of course, vary according to the -relative sizes of the negative and desired picture. With a one-inch -object-glass, which is a very convenient focus, it will have to be -changed usually betwixt one and four feet. The negative must be lighted -by an argand gas-burner or camphine-lamp, and the rays rendered as -parallel as possible by the use of a large lens placed betwixt the -light and the negative. It is not easy to arrange the apparatus so as -to get the light _uniform_; but a little practice will soon do away -with this difficulty. Ordinary ground-glass is too coarsely grained -to focus upon, as the magnifying power used to examine the minute -reflection must be considerable. One of the slides must therefore be -coated with the collodion, submitted to the silver-bath, and after -washing with water be allowed to dry. Upon this may be focussed -the reflected image, and its minuteness examined with a powerful -hand-magnifier, or another microscope placed behind in a horizontal -position. When the utmost sharpness of definition is obtained, it -is usually required to remove the plate a little distance from the -object-glass, as object-glasses for the microscope are slightly “over -corrected,” and the chemical rays which accomplish the photography -are beyond the visual ones. The exact distance required to give a -picture to bear the greatest enlargement cannot be given by rule; but -experiments must be made at first, and it will always be the same with -the object-glass which we have tested. - -The plate may now be prepared as in ordinary photography, and placed -upon the stage whilst the light is shaded. When all is ready, the -shade is removed and the process allowed to go on, usually for thirty -or forty seconds; but no certain rule can be given as to the required -time, on account of various collodions, lamps, and powers being used. -It may be here mentioned, that it is well to contrive some little frame -to receive the prepared plate, as the silver bath solution is liable to -get upon the microscope stage and so, to say the least, disfigure it. -When the exposure has been continued sufficiently long, the picture -may be developed by any of the ordinary methods, but some of the best -productions have been brought out by the aid of pyrogallic and citric -acid solution, with the addition of a little alcohol. The “fixing” may -be effected by a strong solution of hypo-sulphite of soda, and the -picture must then be very well washed with pure water. When dry, the -photograph must be mounted with Canada balsam, in the same manner as -any ordinary object; but great heat must not be used, or the picture -may be injured. - -When ordinary daylight is employed for this purpose, a dark slide -will be required for the prepared plate, in the same way as for -photographing landscape, &c. These dark slides are generally made by -each individual to suit his particular arrangements of negatives, &c.; -but it may be here recommended that the operator should always focus in -the same slide which he is about to use, as so small a difference in -distance lies betwixt perfection and failure. - -For an ordinary student, perhaps the above method is that which is the -most readily used, and consequently the most generally available; but -almost every one has a different arrangement of microscope, &c., by -which he procures these minute pictures. Mr. Shadbolt (one of our most -successful photographers) gives the following instructions:--“Having -removed the upper stage plate of a large compound microscope, I replace -it with one of wood, supplied with guide pins of silver wire, in order -to admit of its supporting a slip of glass coated with collodion, and -excited in the nitrate of silver bath in the usual way. If the ordinary -brass stage plate were left undisturbed, it is obvious that it and the -excited slip of glass would be mutually destructive. - -“The microscope is now to be placed in a horizontal position, the -objective, intended to produce the picture, made to occupy the place -usually filled by the achromatic condenser on the _sub-stage_ of the -microscope, while _another_ objective is screwed into the lower end of -the body of the instrument, which is used not only to focus with, but -also to make the requisite allowance for actinic variation. - -“The negative intended to be reduced is then arranged vertically, with -its centre in the axis of the microscopic body, at a distance of from -two to four feet from the lower object-glass, and with a convenient -screen of card, wood, or thick paper, to cut off any extraneous light -that would otherwise pass beyond the limits of the picture. - -“A small camphine-lamp is employed for the purpose of illuminating the -negative, having a good bull’s-eye lens as a condenser, so arranged -with its flat side next the lamp that the refracted rays shall just -fill the whole of a double convex lens of about six inches in diameter, -the latter being placed in such a position as to refract the rays of -light in a parallel direction upon the negative. By this arrangement -the _bull’s-eye lens_ of about two inches and a half in diameter -_appears_ as the source of the light instead of the small flame of the -lamp. - -“By using a bat’s-wing gas-burner of a good size, a _single_ lens, -instead of the two, may be so placed as to give the necessary -uniformity of illumination.” - -This arrangement requires the same care in working as that before -mentioned, the pictures being produced, developed, and fixed by the -same treatment. - -As before stated, almost every manipulator makes some small changes in -the method of producing these minute pictures; but the rules given, -though far from new, are sufficient for all purposes; and I may state -with truth, that those which I procured when these wonders were quite -new, are fully equal in every respect to the best usually met with at -the present time. - -With these instructions I shall close my Handbook, as I believe that -every branch of Preparation and Mounting of Microscopic Objects has -been treated of. Not that the beginner can expect that he has nothing -to do except read this to be able to mount everything; but there are -difficulties from which he may be freed by instruction, when otherwise -he would have been compelled to learn by failure alone. I may, here, -however, repeat certain advice before given,--that, when practicable, -it is a good thing to mount each object by two or more different -methods, as very frequently one feature is best shown dry, another in -liquid, and a third in balsam. Secondly, let the _mounting_ be studied -thoroughly, as no part of the microscopic science is more worthy of -thought than this. And lastly, let no failures prevent you following -up what will assuredly one day become a source of great pleasure, and -render your daily “constitutional walk,” which is often dull in the -extreme, very delightful, as it will afford you some new wonder in -every hedge-row. - - - - -INDEX. - - - Air-bubbles, 56. - - Air-pump, 13; - use of, 57. - - Alcock, Dr., on tongues of Mollusca, 118. - - Algæ, mounting of, 91. - - Anacharis alsinastrum, rotation in, 143; - to cultivate, 144. - - Animal tissues, dissection of, 114. - - Antennæ of insects, 71; - in preservative liquid, 94. - - Apparatus required in mounting objects, i. - - Arteries, how to distinguish, in injection, 131. - - Asparagus, spiral vessels of, 114. - - Asphaltum, 15; - and india-rubber, as cement and varnish, 18. - - - Bat, circulation of blood in wings of, 142. - - Beale’s, Dr., Prussian blue for injecting, 134; - carmine, 135. - - Bell-glasses, use of, 12. - - Berg-mehl, 40. - - Bermuda earth, 40. - - Bichromate of lead, injection with, 132. - - Bird, Dr. Golding, on preparation of Zoophytes, 65. - - Black-japan, as a cement, 16. - - Black varnish, 18. - - Blood, as a microscopic object, 50; - circulation of, 140–142. - - Bone, sections of, 102; - fossil, 103. - - Brass plate for heating glasses, &c., 13. - - - Cactaceæ, raphides of, 52. - - Camel-hair pencils, use of, 10. - - Canada balsam, 14; - with chloroform, 14, 60, 132; - with turpentine, 14; - air bubbles in, 56; - Dr. Carpenter’s syringe for, 59; - to fill cells with, 60; - mounting of objects in, 56. - - Carbolic acid, 86. - - Carmine injecting fluid, Dr. Beale’s, 135: - Dale & Davies’, 138. - - Cartilage, dissection of, 114. - - Castor oil, as a preservative, 86. - - Cells for dry objects, 6; - with rings of cardboard, 7; - with gutta-percha, 7; - with leather, 7; - with ivory, 8; - with thin glass, 7; - with varnish, 23, 26; - for balsam, 60; - for preservative liquids, 87–89; - Shadbolt’s turntable useful in making, 9. - - Cements, 13–17. - - Chalk, foraminifera from, 63. - - Chara vulgaris, rotation in, 144. - - Chloride of zinc, solution of, 85; - of calcium, solution of, 92. - - Chloroform, use of (_see_ Canada balsam). - - Circulation of blood, 140–142; - of sap (_see_ Rotation). - - Cleanliness in microscopic work, 1. - - Coal, sections of, 99. - - Collection of diatoms, 29. - - Colours for injection, 125–127. - - Condenser, cheap, to make, 20. - - Corals, sections of, 99. - - Corallines, to mount, 48. - - Cover of objects, to remove, 60. - - Crystals, mounting of, dry, 50; - to vary form of, and mount in balsam, 75; - sections of, 109. - - Cuticle of equisetum, &c., 80. - - - Dale & Davies’, carmine injection, 138. - - Deane’s gelatine, 84. - - Decalcifying process for shells, 98. - - Desmidiaceæ, in preservative liquid, 92. - - Diachæa elegans, 53. - - Diamond beetle, 54. - - Diatomaceæ, nature of, 28; - collection of, 29; - in stomachs of fish, 30; - to prepare and mount dry, 30–40; - Mr. Rylands on, 33; - in guano, 39; - fossilized, 40; - mounting in balsam, 61; - mounting in preservative liquids, 92, 93. - - Discs used in mounting, 22; - supporter, Smith & Beck’s, 23. - - Dissection, 111; - microscope for, 111; - instruments for, 112. - - Distilled water, as preservative liquid, 83. - - Doyer’s, M., method of injection, 132. - - Dry objects, to mount, 22. - - - Echinodermata spines, sections of, 99. - - Eel, scales of, 78. - - Eggs of insects, 94. - - Elastic objects, to keep flat upon the slide, 11. - - Electrical cement, 16. - - Equisetaceæ, 80; - spores of, 146. - - Erector, not indispensable, 19. - - Eyes of insects, 70, 54; - of animals injected, 136. - - - Feathers, 73. - - Feet of insects, 54, 71. - - Ferns, 51; - development of spores of, 145. - - Fish, fins and tails of, 50; - scales of, 53, 78; - injection of, 137; - circulation of blood in, 142. - - Flint, sections of, 101. - - Fluid, mounting objects in, 83. - - Flustra avicularis, 79. - - Fly (_see_ Insects). - - Foot of sheep injected, 136. - - Foraminifera, 41; - separation of, 41; - to clean, 42; - to clean from tallow soundings, 42; - to mount, 45, 63; - from chalk, 63. - - Forceps, ordinary and wooden, 11; - bull-nosed, for injection, 123. - - Fossil infusoria, 40. - - Frog, injected, 136; - to show circulation of blood, 140. - - Frog-bit, rotation in, 144. - - Fruit-stones, sections of, 104. - - Fungi, 53, 94. - - - Gastric teeth of insects, 120; - of molluscs, 117. - - Gelatine for injection, 124; - preservative liquid, 84. - - Glass slides, 1; - thin, 3; - thin, to cut, 3; - thin, to measure, 4; - thin, to clean, 5; - cells, to make, 88; - rings for cells, 88; - tubes, 10. - - Glycerine, 84, 94; - jelly, 84, 91. - - Goadby’s fluid, 85. - - Gold-size, 15. - - Grasses, 80. - - Grasshopper, gizzard of, 120. - - Guano, containing Diatomaceæ, 39. - - Gum-water, and modifications of, 17. - - Gutta-percha cells, 7; - for liquids, 87. - - - Hairs, vegetable, 46; - to mount dry, 54; - to mount as polarizing objects, 79; - sections of, 105. - - Hepworth, Mr., on mounting insects, 68. - - Horn, sections of, 104. - - Hot-water bath, use of, 58. - - - Infusoria, in preservative liquid, 92; - fossil, 40. - - Injections, vi., 122; - apparatus for, 122; - colours for, 125; - directions for, 127; - with various colours, 131; - mounting of, 131; - transparent, 133, 138. - - Insects, scales of, 48; - to mount, 49; - legs and feet of, 54, 72; - eyes of, 54, 70; - Mr. Hepworth on mounting, 68; - antennæ of, 71; - mouth of, 72; - tracheæ and spiracles of, 72, 115; - parasitic, 73; - in preservative liquid, 94; - eggs of, 94; - gizzard of, 120; - circulation of blood in, 142. - - Intestines, injected, 136. - - - Knives for dissecting, 112; - Valentin’s, 108. - - - Labelling of objects, 19. - - Lamps, for mounting, 12. - - Larvæ, skins of, 50. - - Leaves, sections of, 107; - scales of, 46, 81. - - Liquid-glue, 16. - - Lungs of animals injected, 137. - - - Mallow, pollen of, 47. - - Marine glue, 15, 88. - - Microscope for dissection, 111. - - Miscellaneous, vii., 140. - - Mites, 73. - - Molluscs, tongues of, 116. - - Mosses, 51; - in preservative fluids, 91. - - Mould (_see_ Fungi). - - Mounting objects, apparatus for, i.; - dry, ii., 22; - in Canada balsam, iii., 56; - in cells, iv., 83. - - Mouse, ear of, 114; - circulation of blood in, 142. - - Mouth of insects, 72. - - Muscle, dissection of, 114. - - - Needles, how to mount, 10; - for dissection, 112; - curved, for injection, 123. - - Nervous tissue, dissection of, 115. - - Nettle leaf, 52. - - Newts, injected, 136. - - - Onion, raphides of, 52. - - Orbitolite, section of, 97. - - Oxalurate of ammonia, crystals of, 75. - - - Palates of Molluscs (_see_ tongues). - - Papers, ornamental, to cover slides, 8, 27. - - Photographs, microscopic, to produce, 147; - Mr. Shadbolt on, 149. - - Pipes for injecting syringe, 122. - - Podura, scales of, 49. - - Polariscope, objects for, 74–82, 104. - - Pollen, 47, 74. - - Polycystina, preparation and mounting of, 63. - - Preservative liquids, iv., 83; - cells suited for, 87–89. - - Prussian blue for injection, 134. - - - Raphides, vegetable, 52, 80. - - Rhinoceros, horn of, 104. - - Rhubarb, spiral vessels of, 113. - - Rings and cross of crystals, 109. - - Rotation of fluid in cells of plants, 143–145. - - Rush, section of, 108. - - Rylands, Mr. T. G., on Diatomaceæ, 33, 93. - - - Salicine, crystals of, 76. - - Saw of watch-spring, 97. - - Scales of fishes, 53, 78; - of leaves, 46, 81; - of insects, 48. - - Scissors, 10; - for dissection, 112. - - Sea-mats, 53. - - Sea-soundings, to cleanse, 42. - - Sealing-wax varnish, 17. - - Sections, 96; - of shells, 97; - of orbitolite, 97; - of spines of Echinodermata, 99; - of corals, 99; - of coal, 99; - of flint, 101; - of teeth, 101; - of bone, 102; - of fruit-stones, 104; - of horn, 104; - of whalebone, 105; - of hairs, 105; - of wood, 106; - of leaves, 107; - of sponges, 108; - of skin, 109; - of crystals, 109; - of seeds, 111. - - Seeds, 47, 74; - sections of, 111; - growth of, 145. - - Shadbolt’s turntable, 9. - - Shells, sections of, 97; - decalcifying, 98; - laminæ of, 98. - - Siliceous cuticles, 80. - - Size for injection, 124. - - Skins of larvæ, 50; - sections of, 109; - sole, 54. - - Slides, glass, for mounting objects, 1; - glass, to clean, 2; - wood, &c., 6; - most useful, 8; - to cover and varnish, 27. - - Spicula, from sponges, &c., 67. - - Spines of Echinus, 99. - - Spiracles of insects, 72, 116. - - Spiral vessels of vegetables, 113. - - Split bristles, use of, 10. - - Sponges, sections of, 108. - - Spores of ferns, development of, 145; - equisetum, 146. - - Starch, preparation and mounting of, 79. - - Sulphate of copper and magnesia, crystals of, 76. - - Syringe for Canada balsam, 59; - for dissection, 113; - for injection, 122. - - - Tadpole, to show circulation of blood of, 141. - - Teeth, sections of, 101. - - Thin glass, to cut, 3; - to measure thickness of, 4; - to clean, 5. - - Thwaites’ preservative liquid, 85. - - Ticks, 73. - - Tissues, animal and vegetable (_see_ Dissection). - - Tongues or palates of Molluscs, 116. - - Tracheæ of insects, 72, 115. - - Transfer of objects, 10. - - Trough for dissection, 113. - - Tubes, glass, 10. - - Turnbull’s, Dr., Prussian blue for injection, 134. - - Turpentine, use of, 57. - - - Universal stand, to make, 20. - - - Valentin’s knife, 108. - - Vallisneria spiralis, rotation in, 143; - to cultivate, 144. - - Varnishes, 17. - - Vegetable objects, to mount dry, 46; - to mount in jelly, 91; - dissection of, 113. - - - Watch-glasses, 12. - - Whalebone, sections of, 105. - - Wood, sections of, 106. - - - Zoophytes, to mount dry, 53; - Dr. Golding Bird on mounting, in balsam, 65; - as polarizing objects, 79. - - -COX AND WYMAN, PRINTERS, GREAT QUEEN STREET, LONDON. - - - - -Transcriber’s Notes - - -Punctuation and spelling were made consistent when a predominant -preference was found in the original book; otherwise they were not -changed. - -Inconsistent hyphenation was not changed. - -Simple typographical errors were corrected; unbalanced quotation -marks were remedied when the change was obvious, and otherwise left -unbalanced. - -The Table of Contents was added by the Transcriber. - -The index was not checked for proper alphabetization or correct page -references. Roman numeral references are to chapters, not to pages. - -Page 106: =T= indicates a boldface, sans-serif “T”. - - - - - -End of the Project Gutenberg EBook of The Preparation & Mounting of -Microscopic Objects, by Thomas Davies - -*** END OF THIS PROJECT GUTENBERG EBOOK PREPARATION OF MICROSCOPIC OBJECTS *** - -***** This file should be named 60225-0.txt or 60225-0.zip ***** -This and all associated files of various formats will be found in: - http://www.gutenberg.org/6/0/2/2/60225/ - -Produced by deaurider, Charlie Howard, and the Online -Distributed Proofreading Team at http://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive) - -Updated editions will replace the previous one--the old editions will -be renamed. - -Creating the works from print editions not protected by U.S. copyright -law means that no one owns a United States copyright in these works, -so the Foundation (and you!) can copy and distribute it in the United -States without permission and without paying copyright -royalties. 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You may copy it, give it away or re-use it under the terms of -the Project Gutenberg License included with this eBook or online at -www.gutenberg.org. If you are not located in the United States, you'll have -to check the laws of the country where you are located before using this ebook. - -Title: The Preparation & Mounting of Microscopic Objects - -Author: Thomas Davies - -Release Date: September 2, 2019 [EBook #60225] - -Language: English - -Character set encoding: UTF-8 - -*** START OF THIS PROJECT GUTENBERG EBOOK PREPARATION OF MICROSCOPIC OBJECTS *** - - - - -Produced by deaurider, Charlie Howard, and the Online -Distributed Proofreading Team at http://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive) - - - - - - -</pre> - - -<h1 class="wspace vspace2"><span class="small">THE</span><br /> -<span class="smaller">PREPARATION & MOUNTING</span><br /> -<span class="xxsmall">OF</span><br /> -MICROSCOPIC OBJECTS.</h1> - -<p class="p2 center vspace2 wspace">BY<br /> -<span class="larger">THOMAS DAVIES.</span></p> - -<p class="p2 center vspace wspace larger"><span class="gesperrt">LONDON</span>:<br /> -ROBERT HARDWICKE, 192, PICCADILLY.<br /> -<span class="small">AND ALL BOOKSELLERS.</span> -</p> - -<hr /> - -<div class="newpage p4 center vtight"> -<p class="center"><i>A New Edition, Revised and Enlarged.<br /> -Price 2s. 6d. plain; 4s. coloured.</i></p> - -<p class="drop-cap"><span class="smcap1">HALF-HOURS WITH THE MICROSCOPE.</span> -A Popular Guide to the Use of the Microscope as a Means of -Amusement and Instruction. With Drawings of 250 objects from -Nature, by TUFFEN WEST. By E. LANKESTER, M.D., F.R.S.</p> - -<p class="center smaller">CONTENTS:</p> - -<div class="ilb"> - -<p class="in0"> -Half an hour on the Structure.<br /> -Half an hour in the Garden.<br /> -Half an hour in the Country.<br /> -Half an hour at the Pondside.<br /> -Half an hour at the Seaside.<br /> -Half an hour Indoors.<br /> -Appendix: the Preparation and Mounting of Objects. -</p> -</div> - -<p class="p2 center"><i>Fcp. 8vo., 6s. beautifully illustrated by hand-painting.</i></p> - -<p class="drop-cap"><span class="smcap1">RUST, SMUT, MILDEW, AND MOULD</span> -under the MICROSCOPE: a Plain and Easy Guide to the Study -of Microscopic Fungi. By M. C. COOKE. Coloured Plates of over -300 Figures.</p> - -<p class="p1 center">London: ROBERT HARDWICKE, 192, Piccadilly; and all Booksellers.</p> -</div> - -<hr /> - -<p><span class="pagenum" id="Page_iii">iii</span></p> - -<div class="chapter"> -<h2 id="PREFACE">PREFACE.</h2> -</div> - -<p class="drop-cap"><span class="smcap1">In</span> bringing this Handbook before the public, the -Author believes that he is supplying a want which -has been long felt. Much information concerning -the “Preparation and Mounting of Microscopic -Objects” has been already published; but mostly -as supplementary chapters only, in books written -professedly upon the Microscope. From this it is -evident that it was necessary to consult a number -of works in order to obtain anything like a -complete knowledge of the subject. These pages, -however, will be found to comprise all the most -approved methods of mounting, together with the -results of the Author’s experience, and that of -many of his friends, in every department of<span class="pagenum" id="Page_iv">iv</span> -microscopic manipulation; and as it is intended to -assist the beginner as well as the advanced student, -the very rudiments of the art have not been -omitted.</p> - -<p>As there is a diversity of opinion as to the best -mode of proceeding in certain cases, numerous -quotations have been made. Wherever this has -been done, the Author believes that he has acknowledged -the source from which he has taken the -information; and he here tenders his sincere -thanks to those friends who so freely allowed him -to make use of their works. Should, however, -anyone find his own process in these pages -<em>unacknowledged</em>, the author can only plead oversight, -and his regret that such should have been -the case.</p> - -<hr /> - -<p><span class="pagenum" id="Page_1">1</span></p> - -<div class="chapter"> -<h2 id="CONTENTS">CONTENTS</h2> -</div> - -<table id="toc" summary="Contents"> - <tr class="small"> - <td> </td> - <td class="tdr">PAGE</td></tr> - <tr> - <td class="tdl">PREFACE</td> - <td class="tdr"><a href="#PREFACE">iii</a></td></tr> - <tr> - <td class="tdc chap" colspan="2">CHAPTER I.</td></tr> - <tr> - <td class="tdl">APPARATUS.</td> - <td class="tdr"><a href="#CHAPTER_I">1</a></td></tr> - <tr> - <td class="tdc chap" colspan="2">CHAPTER II.</td></tr> - <tr> - <td class="tdl">TO PREPARE AND MOUNT OBJECTS “DRY.”</td> - <td class="tdr"><a href="#CHAPTER_II">22</a></td></tr> - <tr> - <td class="tdc chap" colspan="2">CHAPTER III.</td></tr> - <tr> - <td class="tdl">MOUNTING IN CANADA BALSAM.</td> - <td class="tdr"><a href="#CHAPTER_III">56</a></td></tr> - <tr> - <td class="tdc chap" colspan="2">CHAPTER IV.</td></tr> - <tr> - <td class="tdl">PRESERVATIVE LIQUIDS, ETC., PARTICULARLY WHERE CELLS ARE USED.</td> - <td class="tdr"><a href="#CHAPTER_IV">83</a></td></tr> - <tr> - <td class="tdc chap" colspan="2">CHAPTER V.</td></tr> - <tr> - <td class="tdl">SECTIONS AND HOW TO CUT THEM, WITH SOME REMARKS ON DISSECTION.</td> - <td class="tdr"><a href="#CHAPTER_V">96</a></td></tr> - <tr> - <td class="tdc chap" colspan="2">CHAPTER VI.</td></tr> - <tr> - <td class="tdl">INJECTION.</td> - <td class="tdr"><a href="#CHAPTER_VI">122</a></td></tr> - <tr> - <td class="tdc chap" colspan="2">CHAPTER VII.</td></tr> - <tr> - <td class="tdl">MISCELLANEOUS.</td> - <td class="tdr"><a href="#CHAPTER_VII">140</a></td></tr> - <tr class="tpad"> - <td class="tdl">INDEX.</td> - <td class="tdr"><a href="#INDEX">153</a></td></tr> -</table> - -<hr /> - -<div class="chapter"> -<h2 id="THE" class="vspace wspace large"><span class="small">THE</span><br /> -PREPARATION AND MOUNTING<br /> -<span class="small">OF</span><br /> -<span class="larger">MICROSCOPIC OBJECTS.</span></h2> -</div> - -<hr class="narrow" /> - -<h2 id="CHAPTER_I" class="nobreak p2 vspace"><span class="gesperrt">CHAPTER I</span>.<br /> - -<span class="subhead">APPARATUS.</span></h2> - -<p class="in0"><span class="firstword">Before</span> entering into the subject of the setting of Objects -for the Microscope, the student must be convinced of the -necessity of cleanliness in everything relating to the use of -that instrument. In no branch is this more apparent -than in the <em>preparation</em> of objects; because a slide which -would be considered perfectly clean when viewed in the -ordinary way is seen to be far otherwise when magnified -some hundreds of diameters; and those constant enemies, -the floating particles of dust, are everywhere present, and it -is only by unpleasant experience that we fully learn what -<em>cleanliness is</em>.</p> - -<p>Any object which is to be viewed under the microscope -must, of course, be supported in some way—this is now -usually done by placing it upon a glass slide, which on -account of the transparency has a great advantage over other -substances. These “slides” are almost always made of one -size, viz., three inches long by one broad, generally having the -edges ground so as to remove all danger of scratching or -cutting any object with which they may come in contact. -The glass must be very good, else the surface will always<span class="pagenum" id="Page_2">2</span> -present the appearance of uncleanliness and dust. This -dusty look is very common amongst the cheaper kinds of -slides, because they are usually “sheet” glass; but is -seldom found in those of the quality known amongst dealers -by the name of “patent plate.” This latter is more expensive -at first, but in the end there is little difference in the -cost, as so many of the cheaper slides cannot be used for -delicate work if the mounted object is to be seen in perfection. -These slides vary considerably in thickness; care should, -therefore, be taken to sort them, so that the more delicate -objects with which the higher powers are to be used maybe -mounted upon the <em>thinnest</em>, as the light employed in the -illumination is then less interfered with. To aid the microscopist -in this work, a metal circle may be procured, having -a number of different sized openings on the outer edge, by -which the glass slides can be measured. These openings -are numbered, and the slides may be separated according -to these numbers; so that when mounting any object there -will be no need of a long search for that glass which is best -suited to it.</p> - -<p>When fresh from the dealer’s hands, these slides are -generally covered with dust, &c., which may be removed by -well washing in clean rain-water; but if the impurity is -obstinate, a little washing soda may be added, care being -taken, however, that every trace of this is removed by subsequent -waters, otherwise the crystals will afterwards form -upon the surface. A clean linen cloth should be used to -dry the slides, after which they may be laid by for use. -Immediately, however, before being used for the reception of -objects by any of the following processes, all dust must be -removed by rubbing the surface with clean wash-leather or -a piece of cambric, and, <em>if needful</em>, breathing upon it, and -then using the leather or cambric until perfectly dry. Any -small particles left upon the surface may generally be -removed by blowing gently upon it, taking care to allow no -damp to remain.</p> - -<p>We have before said, that any object to be viewed in the<span class="pagenum" id="Page_3">3</span> -microscope must have its support; but if this object is to -be preserved, care must be taken that it is defended from -the dust and other impurities. For this purpose it is necessary -to use some transparent cover, the most usual at one -time being a plate of mica, on account of its thinness; this -substance is now, however, never used, thin glass being -substituted, which answers admirably. Sometimes it is -required to “<em>take up</em>” as little space as possible, owing to -the shortness of focus of the object-glasses. It can be procured -of any thickness, from one-fiftieth to one-two-hundred-and-fiftieth -of an inch. On account of its want of strength -it is difficult to cut, as it is very liable to “<em>fly</em>” from the -point of the diamond. To overcome this tendency as much -as possible, it must be laid upon a thicker piece, previously -made wet with water, which causes the thin glass to adhere -more firmly, and consequently to bear the pressure required -in cutting the covers. The process of cutting being so -difficult, especially with the thinner kinds, little or nothing -is gained by cutting those which can be got from the dealers, -as the loss and breakage is necessarily greater in the hands -of an amateur. It is convenient, however, to have on hand -a few larger pieces, from which unusual sizes may be cut -when required.</p> - -<p>If the pieces required are <em>rectangular</em>, no other apparatus -will be required save a diamond and a flat rule; but if -<em>circles</em> are wanted, a machine for that purpose should be -used (of which no description is necessary here). There -are, however, other contrivances which answer tolerably -well. One method is, to cut out from a thick piece of -cardboard a circle rather larger than the size wanted. -Dr. Carpenter recommends metal rings with a piece of -wire soldered on either side; and this, perhaps, is the -best, as cardboard is apt to become rough at the edge when -much used. A friend of mine uses thin brass plates with -circles of various sizes “turned” through them, and a small -raised handle placed at one end. The diamond must be -passed round the inner edge, and so managed as to meet<span class="pagenum" id="Page_4">4</span> -again in the same line, in order that the circle may be true, -after which they may be readily disengaged. The sizes -usually kept in stock by the dealers are one-half, five-eighths, -and three-quarters inch diameter; but other sizes -may be had to order.</p> - -<p>For the information of the beginner it may be mentioned -here that the price of the circles is a little more than of the -squares; but this is modified in some degree by the circle -being rather lighter. If appearance, however, is cared for -at all, the circles look much neater upon the slides when -not covered with the ornamental papers; but if these last -are used (as will shortly be described) the squares are -equally serviceable.</p> - -<p>As before mentioned, the thin glass is made of various -thicknesses, and the beginner will wish to know which to -use. For objects requiring no higher power than the one-inch -object-glass, the thicker kinds serve well enough; for -the half-inch the medium thickness will be required; while, -for higher powers, the thinnest covers must be used. The -“test-objects” for the highest powers require to be brought -so near to the object-glass that they admit of the very -thinnest covering only, and are usually mounted betwixt -glasses which a beginner would not be able to use without -frequent breakage; but if these objects were mounted with -the common covers, they would be really worthless with the -powers which they require to show them satisfactorily.</p> - -<p>It may be desirable to know how such small differences -as those betwixt the various thin glass covers can be -measured. For this purpose there are two or three sorts of -apparatus, all, however, depending upon the same principle. -The description of one, therefore, will be sufficient. Upon a -small stand is a short metal <em>lever</em> (as it may be termed) -which returns by a spring to one certain position, where it -is in contact with a fixed piece of metal. At the other end -this lever is connected with a “finger,” which moves round -a dial like that of a watch, whereupon are figures at fixed -distances. When the lever is separated from the metal<span class="pagenum" id="Page_5">5</span> -which is stationary, the other end being connected with the -“finger” of the dial, that “finger” is moved in proportion -to the distance of the separation. The thin glass is, therefore, -thrust betwixt the end of the lever and fixed metal, and -each piece is measured by the figures on the dial in stated -and accurate degrees. This kind of apparatus, however, -is expensive, and when not at our command, the thin -glass may be placed edgewise in the stage forceps, and -measured very accurately with the micrometer.</p> - -<p>Cleanliness with the thin glass is, perhaps, more necessary -than with the slides, especially when covering objects which -are to be used with a high power; but it is far more difficult -to attain, on account of the liability to breakage. The -usual method of cleaning these covers is as follows:—Two -discs of wood, about two inches in diameter, are procured, -one side of each being perfectly flat and covered with -clean wash-leather. To the other side of these a small knob -is firmly affixed as a handle, or where practicable the whole -may be made out of a solid piece. In cleaning thin glass, -it should be placed betwixt the covered sides of the discs, -and may then be safely rubbed with a sufficient pressure, -and so cleaned on both sides by the leather. If, however, -the glass be greasy, as is sometimes the case, it must be -first washed with a strong solution of potash, infusion of nut-galls, -or any of the commonly used grease-removing liquids; -and with <em>some</em> impurities water, with the addition of a few -drops of strong acid, will be found very useful, but this last -is not often required.</p> - -<p>The above method of cleaning thin glass should always be -used by beginners; but after some experience the hand -becomes so sensitive that the above apparatus is often -dispensed with, and the glasses, however thin, may be -safely cleaned betwixt the fingers and thumb with a cambric -handkerchief, having first slightly damped the ends of the -fingers employed to obtain firm hold. When the dirt is very -obstinate, breathing upon the glass greatly facilitates its -removal, and the sense of touch becomes so delicate that<span class="pagenum" id="Page_6">6</span> -the breakage is inconsiderable; but this method cannot be -recommended to novices, as nothing but time spent in delicate -manipulation can give the sensitiveness required.</p> - -<p>It was before mentioned that the ordinary glass slides -were sometimes worthless, <em>especially for fine objects</em>, from -having a rough surface, which presented a dusty appearance -under the microscope. This imperfection exists in some -<em>thin glass</em> also, and it is irremediable; so that it is useless -to attempt to cleanse it; nevertheless, care should be taken -not to mistake dirty glass for this roughness, lest good -glass be laid aside for a fault which does not really belong -to it.</p> - -<p>When any object which it is desired to mount is of considerable -thickness, or will not bear pressure, it is evident -that a wall must be raised around it to support the thin -glass—this is usually termed a “cell.” There are various -descriptions of these, according to the class of objects they -are required to protect; and here may be given a description -of those which are most generally used in mounting -“dry” objects, leaving those required for the preservation -of liquids until we come to the consideration of that mode -of mounting. Many have made use of the following slides. -Two pieces of hard wood of the usual size (3 in. by 1 in.), not -exceeding one-sixteenth of an inch in thickness, are taken, and -a hole is then drilled in the middle of one of these -of the size required. The two pieces are then united -by glue or other cement, and left under pressure until -thoroughly dry, when the cell is fit for use. Others substitute -cardboard for the lower piece of wood, which is less -tedious, and is strong enough for every purpose. This class -of “cell” is, of course, fitted for opaque objects only where -no light is required from below; and as almost all such are -better seen when on a dark background, it is usual to fix a -small piece of black paper at the bottom of the cell upon -which to place them. For very small objects the “grain” -which all such paper has when magnified detracts a little -from the merit of this background; and lately I have used<span class="pagenum" id="Page_7">7</span> -a small piece of thin glass covered on the back with black -varnish, and placed the object upon the smooth untouched -side.</p> - -<p>Another method of making these cells is as follows:—Two -“punches,” similar to those used for cutting “gun-wads,” -are procured, of such sizes that with the smaller may be cut -out the centre of the larger, leaving a ring whose side is not -less than one-eighth of an inch wide. These rings may be -readily made, the only difficulty being to keep the sides -parallel; but a little care will make this easy enough. For -this purpose close-grained cardboard may be conveniently -used. It must have a well-glazed surface, else the varnish -or cement used in affixing the thin glass cover sinks into the -substance, and the adherence is very imperfect. When this -takes place it is easily remedied by brushing over the surface -of the cardboard a strong solution of gum or isinglass; -and this application, perhaps, closes also the pores -of the card, and so serves a double purpose. But, of -course, the gum must be <em>perfectly</em> dried before the ring is -used.</p> - -<p>For cardboard, gutta-percha has been substituted, but -cannot be recommended, as it always becomes brittle after -a certain time, never adheres to the glass with the required -firmness, and its shape is altered when worked with even a -little heat. Leather is often used, and is very convenient; -it should be chosen, however, of a close texture, and free -from oil, grease, and all those substances which are laid -upon it by the “dressers.”</p> - -<p>Rings of cardboard, &c., have been rejected by persons of -great experience, because they are of such a nature that -dampness can penetrate them. This fault can be almost, if -not totally, removed by immersing them in some strong -varnish, such as the asphalt varnish hereinafter mentioned; -but they must be left long enough when affixed to the glass -slide to become <em>perfectly dry</em>, and this will require a much -longer time than at first would be supposed.</p> - -<p>There has, however, been lately brought out what is<span class="pagenum" id="Page_8">8</span> -termed the <em>ivory cell</em>. This is a ring of ivory-like substance, -which may be easily and firmly fixed to the glass slide by -any of the commonly-used cements, and so forms a beautiful -cell for any dry objects. They are made of different sizes, -and are not expensive.</p> - -<p>Sometimes slides are used which are made by taking a -thin slip of wood of the usual size (3 in. by 1 in.), in the -centre of which is cut a circular hole large enough to receive -the object. A piece of thin glass is fixed underneath the -slide, forming a cell for the object, which may then be -covered and finished like an ordinary slide. This has the -advantage of serving for transparent objects for which the -before-mentioned wooden slides are unsuitable. A slight -modification of this plan is often used where the thickness -of the objects is inconsiderable, especially with some of the -Diatomaceæ, often termed “test-objects.” The wooden slide -is cut with the central opening as above, and two pieces of -thin glass are laid upon it, betwixt which the diatoms or -other objects are placed, and kept in their proper position -by a paper cover. This arrangement is a good one, insomuch -as the very small portion of glass through which the -light passes on its way to the microscope from the reflector -causes the refraction or interference to be reduced to the -lowest point.</p> - -<p>A novice would naturally think the appearance of some -of the slides above mentioned very slovenly and unfinished; -but they are often covered with ornamental papers, which -may be procured at almost every optician’s, at a cost -little more than nominal, and of innumerable patterns and -colours. How to use these will be described in another -place.</p> - -<p>It is very probable that a beginner would ask his friend -what kind of slides he would advise him to use. Almost -all those made of wood are liable to warp more or less, even -when the two pieces are separate or of different kinds; those -of cardboard and wood are generally free from this fault, -yet the slides, being opaque, prevent the employment of<span class="pagenum" id="Page_9">9</span> -the Lieberkuhn. To some extent glass slides, when covered -with ornamental papers, are liable to the same objection, -as the light is partly hindered. And sometimes the -dampness from the paste, or other substance used to affix -the papers, penetrates to the object, and so spoils it, though -this may be rendered less frequent by first attaching the -<em>thin</em> glass to the slide by some harder cement. Much -time, however, is taken up by the labour of covering -the slides, which is a matter of consideration with some. -Certainly, the cost of the glass slides was formerly great; -but now they are reasonable enough in this respect, so that -this objection is removed. It is, therefore, well to use glass -slides, except where the thin glasses are employed for tests, -&c., as above. When the thin glass circles are placed -upon the slides, and the edge is varnished with black or -coloured rings, the appearance of finish is perfect. The -trouble is much less than with most of the other methods, -and the illumination of the object very slightly interfered -with.</p> - -<p>To varnish the edges of these covers, make circles of any -liquid upon the glass slide, and perform any other “circular” -work mentioned hereafter, the little instrument known as -“Shadbolt’s turntable” is almost indispensable. It is made -as follows:—At one end of a small piece of hard wood is -fixed an iron pivot about one-eighth inch thick, projecting -half an inch from the wood, which serves as a centre upon -which a round brass table three inches in diameter revolves. -On the surface of this are two springs, about one -and a half inches apart, under which the slide is forced and -so kept in position, whilst the central part is left open to -be worked upon. The centre is marked, and two circles half -an inch and one inch in diameter are usually deeply engraved -upon the table to serve as guides in placing the slide, -that the ring may be drawn in the right position. When -the slide is placed upon the “table” underneath the springs, -a camel-hair pencil is filled with the varnish, or other -medium used, and applied to the surface of the glass; the<span class="pagenum" id="Page_10">10</span> -table is then made to revolve, and a circle is consequently -produced, the diameter of which it is easy to regulate.</p> - -<p>Many objects for the microscope may be seriously injured -by allowing the fingers to touch them—many more are -so minute that they cannot be removed in this way at all, -and often it is necessary to take from a mass of small -grains, as in sand, some particular particle. To accomplish -this, there are two or three contrivances recommended: one -by means of split bristles, many of which will readily be -found in any shaving brush when it has been well used. -The bristles when pressed upon any hard surface open, -and when the pressure is removed close again with a spring; -but the use of these is limited. Camel-hair pencils are of -great service for this and many other purposes to the -microscopist. In <em>very</em> fine work they are sometimes required -so small that all the hairs with the exception of one or two -finer pointed ones are removed. A few of various sizes -should always be kept on hand.</p> - -<p>Equally necessary are fine pointed needles. They are very -readily put up for use by thrusting the “eye” end into a -common penholder, so as to be firm. The points may be -readily renewed, when injured, on a common whetstone; but -when out of use they may be protected by being thrust into -a piece of cork.</p> - -<p>Knives of various kinds are required in some branches -of microscopic work, but these will be described where -“dissection,” &c., is treated at some length, as also various -forms of scissors. In the most simple objects, however, -scissors of the usual kind are necessary. Two or three -sizes should always be kept at hand, sharp and in good -order.</p> - -<p>A set of glass tubes, kept in a case of some sort to -prevent breakage, should form part of our “fittings” and -be always cleaned immediately after use. These are -generally from six to ten inches long and from one-eighth -to a quarter of an inch in diameter. One of these should -be straight and equal in width at both ends; one should be<span class="pagenum" id="Page_11">11</span> -drawn out gradually to a fine point; another should be -pointed as the last, but be slightly curved at the compressed -end, in order to reach points otherwise unattainable. It is -well to have these tubes of various widths at the points, as -in some waters the finer would be inevitably stopped. For -other purposes the fine ones are very useful, especially in -the transfer of “preservative liquids” which will come -under notice in another chapter.</p> - -<p>Forceps are required in almost all microscopic manipulations, -and consequently are scarcely ever omitted from the -microscopic box, even the most meagrely furnished; but of -these there are various modifications, which for certain -purposes are more convenient than the usual form. The -ordinary metal ones are employed for taking up small -objects, thin glass, &c.; but when slides are to be held over -a lamp, or in any position where the fingers cannot conveniently -be used, a different instrument must be found. -Of these there are many kinds; but Mr. Page’s wooden -forceps serve the purpose very well. Two pieces of elastic -wood are strongly bound together at one end, so that they -may be easily opened at the other, closing again by their -own elasticity. Through the first of these pieces is loosely -passed a brass stud, resembling a small screw, and fastened in -the second, and through the second a similar stud is taken -and fixed in the first—so that on pressure of the studs the -two strips of wood are opened to admit a slide or other -object required to be held in position. The wood strips are -generally used three or four inches long, one inch wide, and -about one-eighth inch thick.</p> - -<p>Again, some objects when placed upon the glass slide are -of such an elastic nature that no cement will secure the -thin glass covering until it becomes hard. This difficulty -may be overcome by various methods. The following are -as good and simple as any. Take two pieces of wood about -two inches long, three-quarters wide, and one-quarter thick; -and a small rounded piece one inch long and one-quarter in -diameter; place this latter betwixt the two larger pieces.<span class="pagenum" id="Page_12">12</span> -Over one end of the two combined pass an india-rubber -band. This will give a continual pressure, and may be -opened by bringing the two pieces together at the other -end; the pressure may be readily made uniform by paring -the points at the inner sides, and may be regulated -by the strength of the india-rubber band. These bands -may be made cheaply, and of any power, by procuring a -piece of india-rubber tubing of the width required, and -cutting off certain breadths. Another very simple method -of getting this pressure is mentioned in the “Micrographic -Dictionary.” Two pieces of whalebone of the length required -are tied together firmly at each end. It is evident -that any object placed betwixt them will be subject to -continual pressure. The power of this may be regulated -by the thickness and length of the whalebone. This simple -contrivance is very useful.</p> - -<p>Common watch-glasses should always be kept at hand. -They are certainly the cheapest, and their transparency -makes them very convenient reservoirs in which objects -may be steeped in any liquid; as it saves much trouble -to examine cursorily under the microscope, when the air-bubbles -are expelled from insects, &c., &c. They are -readily cleaned, and serve very well as covers, when turned -upside down, to protect any objects from the dust. For -this latter purpose Dr. Carpenter recommends the use -of a number of bell-glasses, especially when one object -must be left for a time (which often happens) in order -that another may be proceeded with. Wine glasses, -when the “legs” are broken, may thus be rendered very -useful.</p> - -<p>As heat is necessary in mounting many objects, a lamp -will be required. Where gas is used, the small lamp known -as “Bunsen’s” is the most convenient and inexpensive. It -gives great heat, is free from smoke, and is readily affixed -to the common gas-burner by a few feet of india-rubber -tubing. The <em>light</em> from these lamps is small, but this is -little or no drawback to their use. Where gas is not<span class="pagenum" id="Page_13">13</span> -available, the common spirit-lamps may be used, which are -very clean and answer every purpose.</p> - -<p>In applying the required heat to the slides, covers, &c., it -is necessary in many cases to ensure uniformity, otherwise -there is danger of the glass being broken. For this purpose -a brass plate at least three inches wide, somewhat longer, -and one-eighth of an inch thick, must be procured. It -should then be affixed to a stand, so that it may be readily -moved higher or lower, in order that the distance from -the lamp may be changed at will, and thus the degree -of heat more easily regulated. This has also the advantage -of enabling the operator to allow his slides, &c., to cool -more gradually, which, in some cases, is absolutely necessary,—as -in fusing some of the salts, &c.</p> - -<p>In order to get rid of air-bubbles, which are frequently -disagreeable enemies to the mounter of objects, an air-pump -is often very useful. This is made by covering a circular -plate of metal with a bell-glass, both of which are ground so -finely at the edges that greasing the place of contact renders -it air-tight. The pump is then joined to the metal plate -underneath, and worked with a small handle like a common -syringe. By turning a small milled head the air may be -allowed to re-enter when it is required to remove the bell-glass -and examine or perform any operation upon the -object. The mode of using this instrument will be described -hereafter, but it may be here stated that substitutes -have been devised for this useful apparatus; but as it is -now to be obtained at a low cost, it is hardly worth while -to consider them. Much time is, in many instances, certainly -saved by its use, as a very long immersion in the -liquids would be required to expel the bubbles, where the -air-pump would remove them in an hour.</p> - -<p>The next thing to be considered is what may be termed -<span class="smcap">Cements</span>, some of which are necessary in every method of -mounting objects for the microscope. Of these will be given -the composition where it is probable the young student can -make use of it; but many of them are so universally kept<span class="pagenum" id="Page_14">14</span> -as to be obtainable almost anywhere; and when small quantities -only are required, economy suffers more from home -manufacture than from paying the maker’s profit.</p> - -<p>Amongst these, <span class="smcap">Canada Balsam</span> may, perhaps, be termed -the most necessary, as it is generally used for the preservation -of many transparent objects. It is a thick liquid -resin of a light amber colour, which on exposure to the -atmosphere becomes dry and hard even to brittleness. For -this reason it is seldom used as a <em>cement</em> alone where the -surface of contact is small, as it would be apt to be displaced -by any sudden shock, especially when old. In the ordinary -method of using, however, it serves the double purpose of -preserving the object and fixing the thin glass cover; -whilst the comparatively large space upon which it lies -lessens the risk of displacement. By keeping, this substance -becomes thicker; but a very little warmth will -render it liquid enough to use even when to some extent -this change has taken place. When heated, however, -for some time and allowed to cool, it becomes hardened -to any degree, which may be readily regulated by the -length of time it has been exposed, and the amount of -heat to which it has been subjected. On account of this -property it is often used with chloroform: the balsam is -exposed to heat until, on cooling, it assumes a glassy appearance; -it is then dissolved in pure chloroform until it -becomes of the consistence of thick varnish. This liquid is -very convenient in some cases; as air-bubbles are much -more easily got rid of than when undiluted Canada balsam -is used. It also dries readily, as the chloroform evaporates -very quickly, for which reason it must be preserved in a -closely-stoppered bottle. It has been said that this mixture -becomes <em>cloudy</em> with long keeping, but I have not found it -so in any cases where I have used it. Should it, however, -become so, a little heat will readily dispel the opacity. The -ordinary balsam, if exposed much to the air whilst being -used, becomes thicker, as has been already stated. It may -be reduced to the required consistency with common turpentine,<span class="pagenum" id="Page_15">15</span> -but I have often found this in some degree injurious -to the transparency of the balsam, and the amalgamation -of the two is by no means perfect. (See also <a href="#CHAPTER_III">Chapter III.</a>) -The cheapness of the article renders it no extravagance to -use it always undiluted; and when preserved in a bottle -with a hollow cover fitting tightly around the neck, both -surfaces being finely ground, it remains fit for use much -longer than in the ordinary jar.</p> - -<p><span class="smcap">Asphaltum.</span>—This substance is dissolved in linseed oil, -turpentine, or naphtha, and is often termed “Brunswick -black.” It is easily worked, but is not generally deemed a -<em>trustworthy</em> cement, as after a time it is readily loosened -from its ground. It is, however, very useful for some purposes -(such as “finishing” the slides), as it dries quickly. -I shall, however, mention a modification of this cement a -little further on.</p> - -<p><span class="smcap">Marine Glue.</span>—No cement is more useful or trustworthy -for certain purposes than this. It is made in various -proportions; but one really good mixture is—equal parts -of india-rubber and gum shellac; these are dissolved in -mineral naphtha with heat. It is, however, much better to -get it from the opticians or others who keep it. It -requires heat in the application, as will be explained in -<a href="#CHAPTER_IV">Chapter IV.</a>; but it is soluble in few, if any, liquids used by -the microscopist, and for that reason is serviceable in the -manufacture of cells, &c. Where two pieces of glass are to -be firmly cemented together, it is almost always employed; -and in all glass troughs, plates with ledges, &c., the beginner -may find examples of its use.</p> - -<p><span class="smcap">Gold Size.</span>—This substance may always be procured at -any colourman’s shop. The process of its preparation is -long and tedious. It is, therefore, not necessary to describe -it here. Dr. Carpenter says that it is very durable, and -may be used with almost any preservative liquids, as it is -acted upon by very few of them, turpentine being its only -true solvent. If too thin, it may be exposed for awhile to -the open air, which by evaporation gradually thickens it.<span class="pagenum" id="Page_16">16</span> -Care must be taken, however, not to render it too thick, as -it will then be useless. A small quantity should be kept on -hand, as it is much more adhesive when <em>old</em>.</p> - -<p><span class="smcap">Liquid Glue</span> is another of these cements, which is made -by dissolving gum shellac in naphtha in such quantity -that it may be of the required consistency. This cement -appears to me almost worthless in ordinary work, as its -adherence can never be relied upon; but it is so often -used and recommended that an enumeration of cements -might be deemed incomplete without it. Even when employed -simply for varnishing the outside of the glass covers, -for appearance’ sake alone, it invariably chips. Where, -however, oil is used as a preservative liquid, it serves very -well to attach the thin glass; but when this is accomplished, -another varnish less liable to “chip” must always be laid -upon it. (See <a href="#CHAPTER_IV">Chapter IV.</a>)</p> - -<p><span class="smcap">Black Japan.</span>—This is prepared from oil of turpentine, -linseed oil, amber, gum anime, and asphalt. It is troublesome -to make, and therefore it is much better to procure it -at the shops. It is a really good cement, and serves very -well to make shallow cells for liquids, as will be described in -<a href="#CHAPTER_IV">Chapter IV.</a> The finished cell should be exposed for a -short time to the heat of what is usually termed a “cool -oven.” This renders it very durable, and many very careful -manipulators make use of it for their preparations.</p> - -<p><span class="smcap">Electrical Cement.</span>—This will be found very good for -some purposes hereinafter described. To make it, melt -<span class="locked">together—</span></p> - -<table class="narrow15" summary="electrical cement"> - <tr> - <td class="tdc">5</td> - <td class="tdc">parts of</td> - <td class="tdl">resin.</td></tr> - <tr> - <td class="tdc">1</td> - <td class="tdc">”</td> - <td class="tdl">beeswax.</td></tr> - <tr> - <td class="tdc">1</td> - <td class="tdc">”</td> - <td class="tdl">red ochre.<a id="FNanchor_A" href="#Footnote_A" class="fnanchor">A</a></td></tr> -</table> - -<div class="footnote"> - -<p><a id="Footnote_A" href="#FNanchor_A" class="fnanchor">A</a> Dr. Griffiths says that the addition of 2 parts of Canada balsam -renders this cement much more adhesive to the glass.</p></div> - -<p>It must be used whilst hot, and as long as it retains even -slight warmth can be readily moulded into any form. It is<span class="pagenum" id="Page_17">17</span> -often employed in making shallow cells for liquids, as before -mentioned.</p> - -<p><span class="smcap">Gum-Water</span> is an article which nobody should ever be -without; but labels, or indeed any substance, affixed to glass -with common gum, are so liable to leave it spontaneously, -especially when kept very dry, that I have lately added five -or six drops of glycerine to an ounce of the gum solution. -This addition has rendered it very trustworthy even on -glass, and now I never use it without. This solution cannot -be kept long without undergoing fermentation, to prevent -which the addition of a small quantity of any essential oil -(as oil of cloves, &c.), or one-fourth of its volume of alcohol, -may be made, which will not interfere in any way with -its use.</p> - -<p>There is what is sometimes termed an <em>extra adhesive</em> -gum-water, which is made with the addition of isinglass, -thus:—Dissolve two drachms of isinglass in four ounces -of distilled vinegar; add as much gum arabic as will give -it the required consistency. This will keep very well, but -is apt to become thinner, when a little more gum may -be added.</p> - -<p>All these, except one or two, are liquid, and must be kept -in <em>stoppered</em> bottles, or, at least, as free from the action of -the air as possible.</p> - -<p>When any two substances are to be united firmly, I have -termed the medium employed “a cement;” but often the -appearance of the slides is thought to be improved by drawing -a coloured ring upon them, extending partly on the cover -and partly on the slide, hiding the junction of the two. -The medium used in these cases I term <span class="smcap">a Varnish</span>, and -hereinafter mention one or two. Of course, the tenacity is -not required to be so perfect as in the <em>cements</em>.</p> - -<p><span class="smcap">Sealing-wax Varnish</span> is prepared by coarsely powdering -sealing wax, and adding spirits of wine; it is then digested -at a gentle heat to the required thickness. This is very -frequently used to “finish” the slides, as before mentioned, -and can easily be made of any colour by employing different<span class="pagenum" id="Page_18">18</span> -kinds of sealing-wax; but is very liable to “chip” and -leave the glass.</p> - -<p><span class="smcap">Black Varnish</span> is readily prepared by adding a small -quantity of lamp-black to gold-size and mixing intimately. -Dr. Carpenter recommends this as a good finishing varnish, -drying quickly and being free from that brittleness -which renders some of the others almost worthless; but it -should not be used in the first process when mounting -objects in fluid.</p> - -<p>Amongst these different cements and varnishes I worked -a long time without coming to any decision as to their -comparative qualities, though making innumerable experiments. -The harder kinds were continually cracking, and -the softer possessed but little adhesive power. To find -hardness and adhesiveness united was my object, and the -following possesses these qualities in a great <span class="locked">degree:—</span></p> - -<table class="narrow20" summary="black varnish"> - <tr> - <td class="tdl">India-rubber</td> - <td class="tdl"> ½ drachm.</td></tr> - <tr> - <td class="tdl">Asphaltum</td> - <td class="tdl"> 4 oz.</td></tr> - <tr> - <td class="tdl">Mineral naphtha</td> - <td class="tdl">10 ”</td></tr> -</table> - -<p class="in0">Dissolve the india-rubber in the naphtha, then add the -asphaltum—if necessary heat must be employed.</p> - -<p class="p2">This is often used by photographers as a black varnish -for glass, and never cracks, whilst it is very adhesive. Dr. -Carpenter, however, states that his experience has not been -favourable to it; but I have used it in great quantities and -have never found it to leave the glass in a single instance -when used in the above proportions. The objections to it -are, however, I think easily explained, when it is known -that there are many kinds of pitch, &c., from coal, sold by -the name of asphaltum, some of which are worthless in -making a microscopic cement. When used for this purpose, -the asphaltum must be genuine and of the best quality -that can be bought. The above mixture serves a double -purpose—to unite the cell to the slide, and also as a “finishing” -varnish. But it is perhaps more convenient to have<span class="pagenum" id="Page_19">19</span> -two bottles of this cement, one of which is thicker than -common varnish, to use for uniting the cell, &c.; the other -liquid enough to flow readily, which may be employed as -a surface varnish in finishing the slides.</p> - -<p>The brushes or camel-hair pencils should always be -cleaned after use; but with the asphalt varnish above -mentioned it is sufficient to wipe off as carefully as possible -the superfluous quantity which adheres to the pencil, as, -when again made use of, the varnish will readily soften it; -but, of course, it will be necessary to keep separate brushes -for certain purposes.</p> - -<p>Here it may be observed that every object should be -labelled with name and any other descriptive item as soon -as mounted. There are many little differences in the -methods of doing this. Some write with a diamond upon -the slide itself; but this has the disadvantage of being not -so easily seen. For this reason a small piece of paper is -usually affixed to one end of the slide, on which is written -what is required. These labels may be bought of different -colours and designs; but the most simple are quite as good, -and very readily procured. Take a sheet of thin writing -paper and brush over one side a strong solution of gum, -with the addition of a few drops of glycerine as above recommended; -allow this to dry, and then with a common -gun-punch stamp out the circles, which may be affixed -to the slides by simply damping the gummed surface, taking -care to write the required name, &c., upon it before damping -it, or else allowing it to become perfectly dry first.</p> - -<p>There is one difficulty which a beginner often experiences -in sorting and mounting certain specimens under the microscope, -viz., the <em>inversion</em> of the objects; and it is often -stated to be almost impossible to work without an erector. -But this difficulty soon vanishes, the young student becoming -used to working what at first seems in contradiction to his -sight.</p> - -<p>Let it be understood, that in giving the description of -those articles which are usually esteemed <em>necessary</em> in the<span class="pagenum" id="Page_20">20</span> -various parts of microscopic manipulation, I do not mean to -say that without many of these no work of any value can -be done. There are, as all will allow, certain forms of -apparatus which aid the operator considerably; but the -cost may be too great for him. A little thought, however, -will frequently overcome this difficulty, by enabling him to -make, or get made, for himself, at a comparatively light -expense, something which will accomplish all he desires. -As an example of this, a friend of mine made what he terms -his “universal stand,” to carry various condensers, &c., &c., -in the following way:—Take a steel or brass wire, three-sixteenths -or one-quarter inch thick and six or eight inches -long; “tap” into a <em>solid</em>, or make rough and fasten with -melted lead into a <em>hollow</em>, ball. (The foot of a cabinet -or work-box answers the purpose very well.) In the centre -of a round piece of tough board, three inches in diameter, -make a hemispherical cavity to fit half of the ball, and -bore a hole through from the middle of this cavity, to allow -the wire to pass. Take another piece of board, about four -inches in diameter, either round or square, and one-and-a-half -or two inches thick, make a similar cavity in its centre -to receive the other half of the ball, but only so deep as to -allow the ball to fit tightly when the two pieces of board are -screwed together, which last operation must be done with -three or four screws. Let the hole for the wire in the upper -part be made conical (base upwards), and so large as only to -prevent the ball from escaping from its socket, in order that -the shaft may move about as freely as possible. Turn a -cavity, or make holes, in the bottom of the under piece, and -fill with lead to give weight and steadiness. This, painted -green bronze and varnished, looks neat; and by having -pieces of gutta-percha tubing to fit the shaft, a great variety -of apparatus may be attached to it.</p> - -<p>Again, a “condenser” is often required for the illumination -of opaque objects. My ingenious friend uses an -“engraver’s bottle” (price 6d.), fills it with water, and -suspends it betwixt the light and the object. Where the<span class="pagenum" id="Page_21">21</span> -light is very yellow, he tints the water with indigo, and so -removes the objectionable colour.</p> - -<p>I merely mention these as examples of what may be done -by a little thoughtful contrivance, and to remove the idea -that nothing is of much value save that which is the work -of professional workmen, and consequently expensive.</p> - -<hr /> - -<p><span class="pagenum" id="Page_22">22</span></p> - -<div class="chapter"> -<h2 id="CHAPTER_II" class="vspace"><span class="gesperrt">CHAPTER II</span>.<br /> - -<span class="subhead">TO PREPARE AND MOUNT OBJECTS “DRY.”</span></h2> -</div> - -<p class="in0"><span class="firstword">The</span> term “dry” is used when the object to be mounted is -not immersed in any liquid or medium, but preserved in its -natural state, unless it requires cleaning and drying.</p> - -<p>I have before stated that thorough cleanliness is necessary -in the mounting of all microscopic objects. I may here add -that almost every kind of substance used by the microscopist -suffers from careless handling. Many leaves with fine hairs -are robbed of half their beauty, or the hairs, perhaps, forced -into totally different shapes and groups; many insects lose -their scales, which constitute their chief value to the microscopist; -even the glass itself distinctly shows the marks -of the fingers if left uncleaned. Every object must also be -<em>thoroughly dry</em>, otherwise dampness will arise and become -condensed in small drops upon the inner surface of the thin -glass cover. This defect is frequently met with in slides -which have been mounted quickly; the objects not being -thoroughly dry when enclosed in the cell. Many of the -cheap slides are thus rendered worthless. Even with every -care it is not possible to get rid of this annoyance occasionally.</p> - -<p>For the purpose of mounting opaque objects “dry,” -<em>discs</em> were at one time very commonly made use of. -These are circular pieces of cork, leather, or other soft substance, -from one-quarter to half inch in diameter, blackened -with varnish or covered with black paper, on which the -object is fixed by gum or some other adhesive substance. -They are usually pierced longitudinally by a strong pin, -which serves for the forceps to lay hold of when being -placed under the microscope for examination. Sometimes<span class="pagenum" id="Page_23">23</span> -objects are affixed to both sides of the disc, which is -readily turned when under the object-glass. The advantage -of this method of mounting is the ease with which the disc -may be moved, and so present every part of the object to -the eye save that by which it is fastened to the disc. On -this account it is often made use of when some particular -subject is undergoing investigation, as a number of specimens -may be placed upon the discs with very little labour, -displaying all the parts. But where exposure to the atmosphere -or small particles of dust will injure an object, no -advantage which the discs may possess should be considered, -and an ordinary covered cell should be employed. Small -pill-boxes have been used, to the bottom of which a piece -of cork has been glued to afford a ground for the pin or -other mode of attachment; but this is liable to <em>some</em> of the -same faults as the disc, and it would be unwise to use these -for permanent objects.</p> - -<p>Messrs. Smith and Beck have lately invented, and are -now making, a beautiful small apparatus, by means of -which the disc supporting the object can be worked with -little or no trouble into any position that may prove most -convenient, whilst a perforated cylinder serves for the -reception of the discs when out of use, and fits into a case -to protect them from dust. A pair of forceps is made for -the express purpose of removing them from the case and -placing them in the holder.</p> - -<p>All dry objects, however, which are to be preserved should -be mounted on glass slides in one of the cells (described in -<a href="#CHAPTER_I">Chapter I.</a>) best suited to them. Where the object is to be -free from pressure, care must be taken that the cell is deep -enough to ensure this. When the depth required is but -small, it is often sufficient to omit the card, leather, or other -circles, and with the “turn-table” before described, by -means of a thick varnish and camel-hair pencil, to form a -ring of the desired depth; but should the varnish not be of -sufficient substance to give such “walls” at once, the -first application may be allowed to dry, and a second<span class="pagenum" id="Page_24">24</span> -made upon it. A number of these may be prepared at the -same time, and laid by for use. When liquids are used (see -<a href="#CHAPTER_IV">Chapter IV.</a>), Dr. Carpenter recommends gold-size as a good -varnish for the purpose, and this may be used in “dry” -mountings also. I have used the asphaltum and india-rubber -(mentioned in <a href="#CHAPTER_I">Chapter I.</a>), and found it to be everything -I could wish. The cells, however, must be <em>thoroughly -dry</em>, and when they will bear the heat they should be baked -for an hour at least in a tolerably cool oven, by which -treatment the latter becomes a first-rate medium. All dry -objects which will not bear pressure must be firmly fastened -to the slide, otherwise the necessary movements very often -injure them, by destroying the fine hairs, &c. For this -purpose thin varnishes are often used, and will serve well -enough for large objects, but many smaller ones are lost by -adopting this plan, as for a time, which may be deemed long -enough to harden the varnish, they exhibit no defect, but in -a while a “wall” of the plastic gum gathers around them, -which refracts the light, and thus leads the student to -false conclusions. In all <em>finer</em> work, where it is necessary -to use any method of fixing them to the slide, a solution of -common gum, with the addition of a few drops of glycerine -(<a href="#CHAPTER_I">Chapter I.</a>), will be found to serve the purpose perfectly. -It must, however, be carefully filtered through blotting paper, -otherwise the minute particles in the solution interfere with -the object, giving the slide a dusty appearance when under -the microscope.</p> - -<p>When mounting an object in any of these cells, the glass -must be thoroughly cleaned, which may be done with a -cambric handkerchief, after the washing mentioned in <a href="#CHAPTER_I">Chapter -I.</a> <em>If the object be large</em>, the point of a fine camel-hair -pencil should be dipped into the gum solution, and a minute -quantity of the liquid deposited in the cell where the object -is to be placed, but not to cover a greater surface than -the object will totally hide from sight. This drop of gum -must be allowed to dry, which will take a few minutes. -Breathe then upon it two or three times, holding the slide<span class="pagenum" id="Page_25">25</span> -not far from the mouth, which will render the surface adhesive. -Then draw a camel-hair pencil through the lips, -so as to moisten it slightly (when anything small will adhere -to it quite firmly enough), touch the object and place it -upon the gum in the desired position. This must be done -immediately to ensure perfect stability, otherwise the gum -will become at least partially dry and only retain the object -imperfectly.</p> - -<p>When, however, the objects are so minute that it would -be impossible to deposit atoms of gum small enough for -each one to cover, a different method of proceeding must be -adopted. In this case a small portion of the same gum -solution should be placed upon the slide, and by means of -any small instrument—a long needle will serve the purpose -very well—spread over the surface which will be required. -The quantity thus extended will be very small, but by -breathing upon it may be prevented drying whilst being dispersed. -This, like the forementioned, should be then allowed -to dry; and whilst the objects are being placed on the prepared -surface, breathing upon it as before will restore the -power of adherence.</p> - -<p>When gum or other liquid cement has been used to fix -the objects to the glass, the thin covers must not be applied -until the slide has been <em>thoroughly dried</em>, and all fear of -dampness arising from the use of the solution done away -with. Warmth may be safely applied for the purpose, as -objects fastened by this method are seldom, if ever, found -to be loosened by it. As objects are met with of every -thickness, the cells will be required of different depths. -There is no difficulty in accommodating ourselves in this—the -deeper cells may be readily cut out of thick leather, card, -or other substance preferred (as mentioned in <a href="#CHAPTER_I">Chapter I.</a>). -Cardboard is easily procured of almost any thickness; but -sometimes it is convenient to find a thinner substance even -than this. When thin glass is laid upon a drop of any -liquid upon a slide, every one must have observed how -readily the liquid spreads betwixt the two: just so when<span class="pagenum" id="Page_26">26</span> -any thin varnish is used to surround an object of little substance, -excessive care is needed lest the varnish should -extend betwixt the cover and slide, and so render it worthless. -The slightest wall, however, prevents this from taking -place, so that a ring of common paper may be used, and serve -a double purpose where the objects require no deeper cell -than this forms.</p> - -<p>Many objects, however, are of such tenuity—as the leaves -of many mosses, some of the Diatomaceæ, scales of insects, -&c.—that no cell is requisite excepting that which is necessarily -formed by the medium used to attach the thin glass -cover to the slide; and where the slide is covered by the -ornamental papers mentioned in <a href="#CHAPTER_I">Chapter I.</a>, and pressure -does not injure the object, even this is omitted, the thin -glass being kept in position by the cover; but slides mounted -in this manner are frequently injured by dampness, which -soon condenses upon the inner surfaces and interferes both -with the object and the clearness of its appearance.</p> - -<p>The thin glass, then, is to be united to the slide, so as to -form a perfect protection from dust, dampness, or other -injurious matter, and yet allow a thoroughly distinct view -of the object. This is to be done by applying to the glass -slide round the object some adhesive substance, and with -the forceps placing the thin glass cover (quite dry and -clean) upon it. A gentle pressure round the edge will then -ensure a perfect adhesion, and with ordinary care there will -be little or no danger of breakage. For this purpose gold-size -is frequently used. The asphalt and india-rubber -varnish also will be found both durable and serviceable. -Whatever cement may be used, it is well to allow it -to become in some measure “fixed” and dried; but -where no cell or “wall” is upon the slide, this is <em>quite -necessary</em>, otherwise the varnish will be almost certain to -extend, as before mentioned, and ruin the object. It may -be stated here that gold-size differs greatly in its drying -powers, according to its age, mode of preparation, &c. -(<a href="#CHAPTER_IV">Chapter IV.</a>)</p> - -<p><span class="pagenum" id="Page_27">27</span> -Should any object be enclosed which requires to be kept -flat during the drying of the cement, it will be necessary to -use some of the contrivances mentioned in <a href="#CHAPTER_I">Chapter I.</a></p> - -<p>When the slide is thus far advanced, there remains the -“finishing” only. Should the student, however, have no -time to complete his work at once, he may safely leave it at -this stage until he has a number of slides which he may -finish at the same time. There are different methods of -doing this, some of which may be here described.</p> - -<p>If ornamental papers are preferred, a small circle must be -cut out from the centre a little less than the thin glass -which covers the object. Another piece of coloured paper is -made of the same size, and a similar circle taken from -its centre also, or both may be cut at the same time. The -slide is then covered round the edges with paper of any -plain colour, so that it may extend about one-eighth of an -inch over the glass on every side. The ornamental paper is -then pasted on the “object” surface of the glass, so that the -circle shows the object as nearly in the centre as possible, -and covers the edges of the thin glass. The other coloured -paper is then affixed underneath with the circle coinciding -with that above. And here I may observe, that when this -method is used there is no necessity for the edges of the -slide to be “ground,” as all danger of scratching, &c., is -done away with by the paper cover.</p> - -<p>Many now use paper covers, about one and a half inches -long, on the upper side of the slide only, with the centre -cut out as before, with no other purpose than that of -hiding the edge of the thin glass where it is united to the -slide.</p> - -<p>The method of “finishing,” however, which is mostly used -at the present time, is to lay a coating of varnish upon the -edge of the thin glass, and extend it some little way on the -slide. When a black circle is required, nothing serves the -purpose better than the gold-size and lamp-black, or the -asphalt and india-rubber varnish, neither of which is liable -to chip; but when used for this, the latter should be rather<span class="pagenum" id="Page_28">28</span> -thinner, as before advised. Some of these varnishes are -preferred of different colours, which may be made by using -the different kinds of sealing-wax, as described in <a href="#CHAPTER_I">Chapter -I.</a>; but they are always liable to the defects there mentioned. -This circle cannot be made in any other way but by one of -those contrivances which have now centred in Shadbolt’s -turntable. A very little practice will enable the young -student to place his slide so that the circle may be uniform -with the edge of the thin glass.</p> - -<p>The slide is now complete, except the addition of the -name and any other particulars which may be desirable. -For this purpose one of the methods described in <a href="#CHAPTER_I">Chapter I.</a> -must be employed.</p> - -<p>Amongst the various classes of microscopic objects now -receiving general attention, the Diatomaceæ may be placed -in a prominent position. They afford endless opportunities -of research, and some very elaborate works have already -been issued concerning them. Professor Smith’s may be -mentioned as one containing, perhaps, the best illustrations. -The young student may wish to know what a diatom is. -The “Micrographic Dictionary” gives the following definition:—“A -family of confervoid Algæ, of very peculiar -character, consisting of microscopic brittle organisms.” -They are now looked upon by almost all of our scientific men -as belonging to the <em>vegetable</em> kingdom, though some few still -assign them to the animal. They are almost invariably -exceedingly small, so that the unaided eye can perceive -nothing on a prepared slide of these organisms but minute -dust. Each separate portion, which is usually seen when -mounted, is termed a “frustule,” or “testule:” this consists -of two similar parts, composed of silica, between and -sometimes around which is a mass of viscid matter called -the “endochrome.” They are found in almost every description -of water, according to the variety: some prefer sea-water, -others fresh, and many are seen nowhere but in that -which is a mixture of both, as the mouths of rivers, &c. -Ditches, ponds, cisterns, and indeed almost every <em>reservoir</em>,<span class="pagenum" id="Page_29">29</span> -yield abundance of these forms. They are not, however, confined -to “present” life; but, owing to the almost indestructible -nature of their siliceous covering, they are found in a fossil -state in certain earths in great abundance, and are often -termed “fossil Infusoria.” Upon these frustules are generally -to be seen lines, or “markings,” of different degrees of -minuteness, the delicacy of which often serves the purpose -of testing the defining power of the object-glasses. Some of -the frustules are triangular, others circular, and, indeed, -of almost every conceivable shape, many of them presenting -us with exquisitely beautiful designs.</p> - -<p>The markings, however, are seldom seen well, if at all, -until the frustules are properly prepared, the different -methods of accomplishing which will be given a little further -on.</p> - -<p>The <em>collection</em> of the fresh diatoms is so closely connected -with their <em>preservation</em>, that a few notes may be given upon -it before we pass on. For this purpose a number of small -bottles must be provided, which may be placed in a -tin box, with a separate apartment for each, so that all -chance of breakage may be done away with. The diatoms -are generally of a light brown colour; and where they are -observed in the water, the bottle may be so placed, with the -mouth closed by the finger, that when the finger is withdrawn -the water will rush in, carrying the diatoms also. -If they are seen upon plants, stones, or any other substance, -they may generally be detached and placed in the bottle. -When there is a green covering upon the surface of the -water, a great quantity of diatoms is usually found amongst -it; as also upon the surface of the mud in those ponds -where they abound. In these cases, a broad flat spoon -will be found very useful, and one is now made with -a covering upon the broader portion of it to protect the -enclosed matter from being so readily carried off whilst -bringing it to the surface again. Where there is any depth -of water, and the spoon will not reach the surface of the -mud, the bottle must be united to a long rod, and being<span class="pagenum" id="Page_30">30</span> -then carried through the upper portion with the mouth -downwards, no water will be received into it; but on reaching -the spot required, the bottle-mouth may be turned up, and -thus become filled with what is nearest.</p> - -<p>From the stomachs of common fish—as the cod, sole, haddock, -&c.—many specimens of Diatomaceæ may be obtained, -but especially from the crab, oyster, mussel, and other shell-fish. -Professor Smith states that from these curious receptacles -he has taken some with which he has not elsewhere -met. To remove them from any of the small shell-fish, it is -necessary to take the fish or stomach from the shell, and -immerse it in strong hot acid (nitric is the best) until the -animal matter is dissolved, when the residue must be -washed and treated as the ordinary Diatomaceæ hereinafter -described.</p> - -<p>Many diatoms are seen best when mounted in a dry -state, the minute markings becoming much more indistinct -if immersed in liquid or balsam; and for this reason those -which are used as test objects are usually mounted <em>dry</em>. -Many kinds also are now prepared in this way, as opaque objects -to be examined with the lieberkuhn, and are exquisitely -beautiful. Others, however, are almost invariably mounted -in balsam; but as these will be again referred to in <a href="#CHAPTER_III">Chapter -III.</a>, and require the same treatment to fit them for the -slide, it will not be out of place to describe the cleaning -and preparation of them here. As before stated, there is -much matter surrounding them which must be got rid of -before the “<em>siliceous</em> covering” can be shown perfectly. -As, however, we may first wish to become acquainted in -some degree with what we have to do, it is well to take a -small piece of <em>talc</em>, and place a few of the diatoms upon it. -This may be held over the flame of the spirit-lamp until all -the surrounding matter is burnt away, and a tolerable idea -may be thus obtained as to the quality of our treasure.</p> - -<p>In some cases it is well to use this burning operation -alone in <em>mounting</em> specimens of diatoms, when they may be -placed in their natural state upon the thin glass, burnt for<span class="pagenum" id="Page_31">31</span> -awhile upon the platinum plate, hereafter described, and -mounted dry or in balsam.</p> - -<p>In the preparation and cleaning of Diatomaceæ, there is -little satisfaction unless these operations have been successfully -performed, as a very small portion of foreign matter -seriously interferes with the object. The mode of preparing -them varies even amongst the most experienced. It will be -found, therefore, most satisfactory to examine the principal -of these separately, although it may be at the risk of some -little repetition.</p> - -<p>The method which is the most frequently made use of is -the following:—Place the “gathering” containing the Diatomaceæ -in a small glass or porcelain vessel, add strong -nitric acid, and, by the aid of Bunsen’s burner or spirit-lamp, -boil for some minutes. From time to time a drop of the -mixture may be put upon a slide, and examined under the -microscope to see if all foreign matter be got rid of. When -the valves are clean, the vessel containing them must be -filled with water, and the whole left for an hour or two, so -that all the diatoms may settle perfectly. The liquid must -then be poured off carefully, or drained away by the aid of -a syphon, so that none of the diatoms are removed with it. -Indeed, it is well to examine the liquid drained off each -time with the microscope, as the finer forms are frequently -lost in the washings. The vessel must then be refilled with -pure water, allowed to settle, and drained as before. This -washing must be repeated until a drop being placed upon -a slide and evaporated leaves no crystals. When it is -desirable to preserve the diatoms in this state before mounting -(which process will be described in another place), they may -be placed in a small phial with a little distilled water.</p> - -<p>There are many cases in which the above method will -not effect a <em>perfect</em> cleansing, as certain substances with -which the diatoms are frequently mixed are not soluble in -<em>nitric acid</em>. For this reason the following method is resorted -to:—Take a quantity of the matter containing the Diatomaceæ -and wash first with pure water, to get rid of all<span class="pagenum" id="Page_32">32</span> -the impurities possible. Allow this to settle perfectly and -decant the water. Add hydrochloric acid gradually, and -when all effervescence has subsided, boil for some minutes by -aid of the lamp. When cool and the particles have subsided, -decant the hydrochloric and add nitric acid. The -boiling must then be repeated until a drop of the liquid -when placed under the microscope shows the valves or -“frustules” clean. After allowing the diatoms to settle, -the acid must be decanted, and pure water substituted. The -washing must be repeated as in the former process until -all the remains of crystals or acid are removed, when the -specimens may be preserved in small phials as stated above.</p> - -<p>Such are the usual modes of treating the Diatomaceæ, -but there are certain cases in which particular methods are -required to give anything like perfect results. Persons of -great experience combine a variety of treatments, and thus -obtain better and more uniform specimens. Perhaps it will -be advantageous to give the young student the process -adopted by one of the most successful preparers of these -objects; but I will first state the different methods of -mounting the cleaned diatoms dry: how to employ Canada -balsam and fluid in their preservation will be elsewhere -described.</p> - -<p>It was before stated that the diatoms when cleansed -might be preserved in small phials of distilled water. -When required for mounting, shake the phial, and with a -thin glass tube or rod take up a drop of the fluid and spread -it upon the surface of the slide in the desired position. -This must then be allowed to dry gradually, or by the aid of -the lamp if necessary, without being shaken or interfered -with, otherwise uniformity of dispersion will be prevented. -When <em>thoroughly</em> dry, a thin ring of one of the adhesive -varnishes—gold-size will be found as good as any—may be -drawn round the diatoms, and allowed to dry in a slight -degree. The slide and thin glass cover should then be -warmed and the latter gently pressed upon the ring of -varnish until the adhesion all round is complete.</p> - -<p><span class="pagenum" id="Page_33">33</span> -As some of the diatoms require object-glasses of extremely -high power, and, consequently, short focus, to show -them, they must be as close to the outer surface of the cover -as possible. For this reason they are sometimes placed -upon the under side of the thin glass, as follows. Clean the -surfaces of the slide and cover, and with the rod or pipe -place the liquid containing the diatoms upon the thin glass, -and dry as before. Trace the ring to receive the cover -upon the slide, and when almost dry, warm both and proceed -as above. Whichever of these methods is employed, the -outer ring of coloured varnish may be applied as elsewhere -described and the slide finished.</p> - -<p>The diatoms are also sometimes mounted betwixt two -thin glasses, as described in <a href="#CHAPTER_I">Chapter I.</a>, so that the light by -which they are examined may receive as little interference -as possible, and that an achromatic condenser may be -brought into focus under the slide.</p> - -<p>Of the various modes of cleaning and mounting the -Diatomaceæ, I believe that the following may be safely -recommended as affording results of the very best quality. -My friend, Mr. T. G. Rylands, gave it to me as that which -he prefers, and I can safely say that his numerous slides are -at least equal to any I have ever seen. I will give it just -as I received it from him, though there may be some little -repetition of what has been said elsewhere, as he does not -appropriate any part of it as his own. He says:—In this -branch of mounting, general rules alone can be laid down, -because the gatherings may contain iron, lime, fine silt, or -vegetable matter under conditions for special treatment, and -consequently the first step should be to experiment on -various kinds.</p> - -<p>In gathering diatoms much labour is saved by judgment and -care; hence it is desirable to get acquainted with them in their -growing condition, so that when recognised upon the sands -or other spots they may be carefully removed by the aid of -the spoon or small tin scoop before described. When growing -upon algæ or other plants, the plants and diatoms<span class="pagenum" id="Page_34">34</span> -together may be carried home, in which case they must be -simply drained and not washed or pressed, in order that the -diatoms be not lost. As it is always desirable to examine -the gathering on the ground, a “Gairdner’s hand microscope” -with powers from 80 to 200 diameters will be found very -useful. The best gatherings are those which represent one -species abundantly. Those which are mixed may be rejected, -unless they are seen to contain something valuable or important, -as the object should be not so much to supply -microscopical curiosities as to collect material which is -available for the study of nature.</p> - -<p>The gathering when carried home should always be -carefully examined before anything is done with it; not -only on account of the additional information thus acquired, -but also because it often happens that a specimen should -be mounted in fluid (see <a href="#CHAPTER_IV">Chapter IV.</a>) in the condition in -which it is gathered, as well as cleaned and mounted in -balsam (<a href="#CHAPTER_III">Chapter III.</a>) and dry.</p> - -<p>Where the gathering is taken from sand, the whole may -be shaken up in water as a preliminary operation, when -much of the sand will be separated by its own weight. -The lime test, however, should be applied, viz.—a small -portion of hydrochloric acid, and if there be effervescence -it must be dissolved out by this means. From Algæ and -other weeds diatoms may be detached by agitating the -whole together in a weak solution of nitric acid—about one -of pure acid to twenty or thirty of water, as it must be -sufficiently weak to free the diatoms without destroying the -matter to which they adhere. The diatoms may then be -separated by sifting through coarse muslin, which will retain -the Algæ, &c. The process of cleaning will vary according -to circumstances. Some gatherings require to be boiled -only a few minutes in nitric acid; but the more general -plan where they are mixed with organic or other foreign -matter, is to boil them in pure sulphuric acid until they -cease to grow darker in colour (usually from a half to one -minute), and then to add, drop by drop to avoid explosions,<span class="pagenum" id="Page_35">35</span> -a cold saturated solution of chlorate of potash until the -colour is discharged, or, in case the colour does not disappear, -the quantity of the solution used is at least equal -to that of the acid. This operation is best performed in a -wide-mouthed ordinary beaker glass,<a id="FNanchor_B" href="#Footnote_B" class="fnanchor">B</a> a test-tube being too -narrow. The mixture whilst boiling should be poured into -thirty times its bulk of cold water, and the whole allowed -to subside. The fluid must then be carefully decanted and -the vessel re-supplied once or twice with pure water, so as -to get rid of all the acid. The gathering may then be -transferred to a small boiling glass or test-tube, and—the -water being carefully decanted—boiled in the smallest -available quantity of nitric acid, and washed as before. -This last process has been found necessary from the frequent -appearance of minute crystals, which cannot otherwise -be readily disposed of without the loss of a considerable -proportion of diatoms.</p> - -<div class="footnote"> - -<p><a id="Footnote_B" href="#FNanchor_B" class="fnanchor">B</a> These glasses are round, about six inches high, and usually contain -about eight ounces. They are rather wider at the bottom, tapering -gradually to the top, and may be generally procured at the chemists, &c.</p></div> - -<p>I may here mention that the washing glasses used by -Mr. Rylands are stoppered conical bottles varying in -capacity from two ounces to one quart; the conical form -being employed to prevent the adherence of anything to -the side; they are “stoppered” to render them available in -the shaking process about to be described.</p> - -<p>The gathering, freed from acid, is now put into two inches -depth of water, shaken vigorously for a minute or two, and -allowed to subside for half an hour, after which the turbid -fluid must be carefully decanted. This operation must be -repeated until all the matter is removed which will not -settle in half an hour. The fluid removed should be examined -by a drop being put upon a slide, as in some cases -very light diatoms have been found to come off almost -pure in one or more of these earlier washings. The quantity -of water and time of subsidence given may be taken<span class="pagenum" id="Page_36">36</span> -generally, but may require to be modified according to -circumstances and the judgment of the operator. By the -repetition and variation of this process—the <em>shaking</em> being -the most important part—the gathering, if a <em>pure</em> one, will -be sufficiently clean. If, however, it contains a variety of -species and forms, it may require to be divided into <em>different -densities</em>.</p> - -<p>In some cases, however, it is best to divide the gathering -as a <em>preliminary</em> operation, which may be done by agitating -it in a quantity of water and decanting what does not -readily subside. The heavier and the lighter portions are -then to be treated as two separate boilings. But when the -cleansing has been carried to the above stage and this -division is required, the plan must be somewhat as follows:—The -gathering must be shaken in a test-tube with six -inches of water, and then allowed to subside until one inch -at the top remains pure. About three inches are then to -be carefully withdrawn by a pipette, when the tube may be -filled up and the operation repeated. The three lower -inches also may then be decanted and examined. The -gathering is thus divided into three portions, viz.—that -which was withdrawn by the pipette, that which remained -floating in the lower three inches of water in the tube, and -that which had settled at the bottom. An examination of -these will inform the operator how to obtain that particular -density of gathering which he desires, and how far it is -worth while to refine this process of elutriation; for in -cases of necessity any one, or all three, of these densities -may be operated upon in the same way to separate a -particular diatom.</p> - -<p>As occasional aids, it may be remarked, that in some cases -<em>liquor ammoniæ</em> may be used in place of water, as it often -separates fine dirt, which is not otherwise easily got rid -of. Some fossil deposits require to be treated with a boiling -solution of carbonate of soda to disintegrate them; but this -operation requires great care, lest the alkali should destroy -the diatoms. Vegetable silicates also sometimes require to<span class="pagenum" id="Page_37">37</span> -be removed by a solution of carbonate of soda; but as the -frustules of the diatoms themselves are but <em>vegetable silica</em>, -even more care is required in this case. It may be well -to mention, that some diatoms are so imperfectly siliceous -that they will not bear <em>boiling</em> in acid at all. Some of -these may be allowed to stand in cold nitric acid some time, -whilst others of a smaller and more delicate character -should, when possible, be treated with distilled water -alone.</p> - -<p>We will now consider the mode of mounting the prepared -diatoms, which, if used dry (as described in this chapter), -should be carefully washed two or three times with the -purest distilled water. In this branch, as in every other, -each collector gives preference to that method in which he -is an adept. Thus the diatoms may be placed on the -under side of the cover, to be as near to the object-glass -as possible, or upon the slide itself; and each plan has -its advocates. Whichsoever of these is used, nothing seems -more simple to the novice than a tolerably equal dispersion -of the objects upon the slide or cover; but this is by no -means so readily accomplished, consequently I give Mr. -Rylands’ method, as his slides are perfect in this respect -also. He always places the diatoms upon the thin glass -cover. It is not sufficient, as is frequently thought, to -take a drop of liquid containing the cleansed material and -spread it upon the cover or slide, as without some additional -precaution that uniform and regular distribution of the -specimens is not obtained which is desirable. In order to -effect this, let a drop of the cleansed gathering be diluted -sufficiently for the purpose—how much must be determined -in each case by experiment—and let the covers to be -mounted be cleaned and laid upon the brass plate. (See -<a href="#CHAPTER_I">Chapter I.</a>) By means of a glass tube, about one-twelfth of -an inch in diameter, stopped by the wetted finger at the -upper end, take up as much of the diluted material as will -form a moderately convex drop extending over the whole -cover. When all the covers required are thus prepared,<span class="pagenum" id="Page_38">38</span> -apply a lamp below the brass plate, and raise the temperature -to a point just short of boiling. By this means -the covers will be dried in a few minutes, and the specimens -equally distributed over the whole area. The spread of -the fluid upon the covers is facilitated by breathing upon -them; and, to insure uniformity, care must be taken to -avoid shaking them whilst drying. The best plan is to -mount at least half a dozen at once.</p> - -<p>Before mounting, Mr. Rylands always burns the diatoms -upon the glass at a dull red heat, whether they are used -with balsam or dry. This burning, he says, is not only -an additional cleaning process, but it effectually fixes the -diatoms, and prevents them floating out if mounted -with balsam. The thinnest covers may be burnt without -damage if they are placed upon a small piece of -platinum foil of the size required, which should be about -one-hundredth of an inch thick, perfectly flat, and having -three of its edges slightly bent over, so as to prevent its -warping with the heat. The small flame of a spirit-lamp, -or, where there is gas, a Bunsen’s burner, may be employed. -The cover should be shaded from direct daylight, that the -action of the flame may be observed more perfectly. Care -must then be taken to raise the temperature only to the -dull red heat before mentioned. The cover will then be -in a fit state for mounting as required.</p> - -<p>It has been stated in another place that it is assumed -the operator is not mounting diatoms simply as microscopic -objects, but as instructive specimens. It is not, therefore, -sufficient to take a single slide as all that is required, but -to have the same diatom prepared in as many ways as -possible. The following are the <span class="locked">principal:—</span></p> - -<blockquote> - -<p>1. Mounted crude in fluid (see <a href="#CHAPTER_IV">Chapter IV.</a>).</p> - -<p>2. Burnt crude upon the cover, and mounted dry or in -balsam (as before mentioned).</p> - -<p>3. Mounted dry or in balsam (see <a href="#CHAPTER_III">Chapter III.</a>), after -the cleansing process already described.</p></blockquote> - -<p>I will here give Mr. Rylands’ method of mounting them<span class="pagenum" id="Page_39">39</span> -<em>dry</em>, the fluid and balsam preparations being noticed in their -respective chapters. The slide with the ring of asphalt, -or black varnish, should have been prepared some weeks -previously, in order to allow it to dry thoroughly. When -required, it must be held over the spirit-lamp or Bunsen’s -burner until the ring of varnish is softened. The burnt -cover, having been heated at the same time, must then be -taken in the forceps and pressed upon the softened varnish -until it adheres all round. When cold, an outer ring of -asphalt completes the slide.</p> - -<p>Such is the method which my friend Mr. T. G. Rylands -employs in the preparation of diatoms for the microscope. -I have said enough concerning his results. It is to be -feared, however, that to some these several modes of operation -may appear lengthy and complicated; but if read -carefully, and the experiments tried, they will be found -simple enough in practice, and to occupy much less time -than an intelligible description would lead the novice to -believe necessary.</p> - -<p>One of the most fertile as well as the most curious magazines -of Diatomaceæ is <em>guano</em>. The siliceous forms contained -therein have been devoured by sea-birds and passed through -the stomach uninjured, and after lying for ages may be -cleaned and classified. Many of these are not elsewhere -met with, so that the student who is desirous to enter into -the study of Diatomaceæ must be instructed as to the best -mode of obtaining them from this source. The particulars -to be observed so closely resemble those before mentioned -in the treatment of the ordinary diatoms, that it will be -sufficiently explicit to give the outlines of the process. The -guano must be first washed in pure water, allowed to subside -perfectly, and the liquid then poured off. This must -be repeated until the top fluid is clear, and care taken not -to decant the liquid until perfect subsidence has taken -place. The deposit must then be treated with hydrochloric -acid with a gentle heat for an hour or two, adding a little -fresh acid at intervals as long as it excites any effervescence<span class="pagenum" id="Page_40">40</span> -After this nitric acid must be substituted for the hydrochloric, -and the heat kept up to almost boiling-point for -another hour at least, adding a little fresh acid as before. -When this ceases to act, the deposit must be allowed to -settle perfectly and the acid poured off. All traces of the -acid must now be washed away with pure water, when the -remains will be Diatomaceæ, the sand contained in the -guano, and a few other forms. Some of these may be -mounted dry, as before mentioned, but the greater portion -should be put up in Canada balsam as described in -<a href="#CHAPTER_III">Chapter III.</a></p> - -<p>Such is the ordinary method for the treatment of guano; -but Mr. Rylands’ mode of proceeding with ordinary Diatomaceæ -(before given) will be found equally successful with -these deposits.</p> - -<p>The fossil Infusoria (as they were formerly called) are now -termed Diatomaceæ, and are found in various parts of the -world—“Bermuda earth,” “Berg-mehl” from Norway, deposit -from Mourne Mountain in Ireland, &c. They are found in -immense quantities, and afford the microscopist innumerable -objects. The same treatment as that usually employed for -the Diatomaceæ must be followed with these deposits, but -as they are sometimes obtained in hard masses, disintegration -is first necessary. To effect this, they are usually boiled -for a short time in diluted <i xml:lang="la" lang="la">liquor potassæ</i>, which will soon -cause the mass to fall into a mud-like deposit. Water -must then be immediately added, in order that all further -action of the <i xml:lang="la" lang="la">liquor potassæ</i> may be stopped, otherwise the -objects searched for will be dissolved. For this reason it is -necessary to understand what substance is being dealt with, -because some deposits are much finer and acted upon more -readily than others.</p> - -<p>In mounting these objects, some are so delicate that they -are almost invisible when balsam is used with them; they -are therefore usually mounted <em>dry</em>. Others, however, are -much coarser, and may be mounted in balsam like the Diatomaceæ -mentioned in <a href="#CHAPTER_III">Chapter III.</a></p> - -<p><span class="pagenum" id="Page_41">41</span> -The common Infusoria cannot be mounted dry with any -great success, though a few may be placed upon the glass -slide and allowed to dry naturally, when their characters -will be very well shown. To obtain anything like a natural -appearance, they must be put up in fluid as in <a href="#CHAPTER_IV">Chapter IV.</a></p> - -<p>Next to the Diatomaceæ, no class of microscopic objects has -been more looked into of late than the Foraminifera. These -animals are almost all marine, having a jelly-like body enclosed -in one or more chambers of shell generally composed of -carbonate of lime. The shells are made with minute orifices, -through which the pseudopodia (false feet) are extended by -which the animal is enabled to lay hold of anything and -draw itself along. From the possession of these orifices -they derive their name, as <em>foramen</em> means a door or opening. -They have been found in every depth of sea hitherto -sounded, each depth being abundant in certain species; the -lowest beds containing the greatest number of specimens, -though with less variation of kinds. In chalk they are found -in a fossil state, and may readily be shown (see <a href="#CHAPTER_III">Chapter -III.</a>); in limestone and other hard stones they are abundant, -and some mountains are composed principally of these -shells.</p> - -<p>The methods of obtaining Foraminifera are various. Many -may be found upon seaweeds, which should always be examined -as soon as possible after gathering. They are found -in masses upon some coasts where the waves have carried -and left them; but they are to be found the most abundantly -in sand or mud dredged from the bottom of the sea. They -must, however, be cleansed and separated from the mass of -impurity with which they are usually mixed. This may be -done in various ways, according to the nature of the accompanying -matter. If sand alone, as is frequently the case, -the whole mass must be <em>thoroughly</em> dried, and then stirred -up in clean water. The sand will soon subside by its own -weight, but the chambers of the Foraminifera, being filled -with air, will float upon the surface, and may be skimmed -off. There is, however, one objection to this mode of proceeding—some<span class="pagenum" id="Page_42">42</span> -of these objects are so minute, the chambers -containing comparatively so small a quantity of air, that they -sink and are cast away with the refuse sand. On this -account it is preferable to take the trouble of searching -certain soundings under the microscope, using the camel-hair -pencil, or some other contrivance before mentioned, to -extract those objects which are required. To clean the -Foraminifera, Professor Williamson advises to transfer the -specimens to an evaporating dish containing a weak solution -of caustic potash. This must be boiled for “some -moments,” when the organic matter will be entirely dissolved, -and the calcareous shells left free from impurity. They -must now be well washed in water, so that all alkaline -matter may be entirely got rid of.</p> - -<p>If the specimens are in <em>mud</em>, we must proceed in a different -way:—Stir up the whole mass in water, and allow -it to stand until the heavier portion has sunk to the bottom; -the water may then be poured off and examined to see if -there are any objects contained in it. This process must -be repeated until the water comes off quite clear, when (if -the search is for Foraminifera only) the solution of caustic -potash may be used as before mentioned. However the -soundings, &c., are cleaned, it is necessary to assort them -under the microscope with the camel-hair pencil or other contrivance, -as it is impossible to obtain them fit for mounting -without undergoing this process.</p> - -<p>The sea soundings taken by order of Government are -drawn from the bottom in a kind of apparatus ingeniously -made for the purpose, and the sand, mud, &c., are brought -up in their original state. Common soundings, however, -are taken by lowering a heavy piece of lead coated with -tallow, which consequently brings up a small portion of the -matter from the bottom. Mr. George Mosley, the late -Secretary of the Manchester Microscopic Society, obtained -numbers of the “scrapings” from the sounding leads. To -make any use of these it is, of course, necessary to free them -from all traces of the tallow. Mr. Dancer places the<span class="pagenum" id="Page_43">43</span> -sounding in a basin and pours boiling water upon it, which -causes the melted grease to rise to the surface. When -cold, this may be removed, and the water carefully decanted. -The operation may be repeated until no grease appears, -when the water may be withdrawn and <i xml:lang="la" lang="la">liquor ammoniæ</i> -used, which will form a soapy solution with any remaining -grease. This must be treated with hot water for the final -washing. Care must be taken lest the finer forms be carried -away in decanting the washing liquid. Should it be wished -to make certain as to this point, each washing should be -examined under the microscope. In some cases the process -of Mr. Dancer will prove sufficient. Mr. Dale, however, -gives a method of accomplishing the same result, which is -much more readily completed; and as the results cannot -be found fault with, I will here give it in full:—It is now -well known that one of the products obtained from the -naphtha of coal-tar is a volatile, oily substance, termed -<em>benzole</em> (or, by French chemists, <i xml:lang="fr" lang="fr">benzine</i>), whose boiling-point, -when pure, is about 180° Fahrenheit, which is a -perfect solvent for fatty substances. In a capsule, previously -warmed on a sand-bath, Mr. Dale mixes with the -tallow soundings benzole, whose boiling-point may be about -200°, until sufficiently diluted so as to run freely, pressing -the lumps with a glass rod until thoroughly mingled; the -solution and its contents are then poured into a paper -filter, placed in a glass funnel; the capsule is again washed -with benzole, until the whole of the gritty particles are -removed into the filter. A washing-bottle is then supplied -with benzole, and the contents of the filter washed to the -bottom until that liquid passes off pure, which may be -tested by placing a drop from the point of the funnel on a -warm slip of glass or bright platinum, when, if pure, the -benzole will evaporate without residue or tarnish; if grease -be present, the washings must be continued until they are -free from it. After rinsing through <em>weak</em> acid, or alcohol, -for final purification, the calcareous forms will be ready for -mounting.</p> - -<p><span class="pagenum" id="Page_44">44</span> -The filter and its contents may be left to dry spontaneously, -when the latter can be examined by the microscope. -Should time be an object, rapid drying may be -effected by any of the usual methods; one of which, -recommended by Mr. Dale, is to blow a stream of hot air -through a glass tube held in the flame of a Bunsen’s burner. -The lower the boiling-point of the benzole, the more readily -can the specimens be freed from it. A commoner quality -may be used, but it is more difficult to dry afterwards.</p> - -<p>Pure benzole being costly, this may appear an expensive -process; but, with the exception of a trifling loss by -evaporation, the whole may be recovered by simple distillation. -The mixture of tallow and benzole being placed -in a retort in a hot-water, a steam, or a sand bath, the -benzole will pass into the receiver, and the tallow or other -impurities will remain in the retort. When the whole of -the benzole has distilled over, which is ascertained by its -ceasing to drop from the condenser, the heat is withdrawn -and the retort allowed to cool before the addition of fresh -material. Half a dozen to a dozen filters, each with its -specimen, can be in process at the same time; and the distillation -of the recovered benzole progresses as quickly as -the filtration, which was practically proved on the occasion -named. Great caution in the use of benzole is to be taken -in the approach of lights to the inflammable vapour.</p> - -<p>After the Foraminifera and calcareous forms have been -removed, the residue may be treated with acids and levigation -in the usual manner, to obtain siliceous forms and -discs, if there are any present; but to facilitate their -deposition, and to avoid the loss of any minute atoms -suspended in the washings, I would suggest the use of -filtration. The conical filter is unsuitable, as the particles -would spread over too great a surface of paper; but glass -tubes open at both ends (such as broken test-tubes) will be -found to answer, the broad end covered with filtering paper, -and over that a slip of muslin tied on with a thread to -facilitate the passage of the water and prevent the risk of<span class="pagenum" id="Page_45">45</span> -breaking the paper. Suspend the tube over a suitable -vessel through a hole cut in thin wood or cardboard, pour -in the washings which can be thus filtered and then dried. -The cloth must be carefully removed, the paper cut round -the edges of the tube, and the diatoms on the paper disc -may be removed by a camel-hair pencil or otherwise, ready -for mounting. Thus many objects may be preserved which -would be either washed away or only be obtained by a more -tedious process.</p> - -<p>Such is Mr. Dale’s method of cleaning the soundings -from the tallow, and as it thoroughly accomplishes its end, -and is alike effective and not injurious to Foraminifera and -diatoms, it may be safely recommended. The weak solution -of caustic potash before advised for Foraminifera, must not -be used where it is desired to preserve the diatoms, as they -would certainly be injured, or destroyed altogether, if this -agent were employed.</p> - -<p>In fixing the Foraminifera upon the slide, no better plan -can be followed than the “dry cells” and gum recommended -in the early parts of this chapter. Owing to their thickness -and composition, most of them are opaque objects only; but -they are exquisitely beautiful, and require no particular care, -except in allowing the cell, &c., to be perfectly dry, when -the cover is placed upon it, or the damp will certainly -become condensed upon the inner side, and the examination -seriously interfered with.</p> - -<p>Many of the Foraminifera require cutting into sections if -it is wished to examine the internal structure, &c.,—“decalcifying” -is also desirable in some cases;—both of these processes -will be found described at length in the chapter on -Sections and Dissection.</p> - -<p>When more than one specimen of some particular shell -is obtained, it is better to place them upon the slide in different -positions, so as to show as much of the structure as -possible. I will conclude this subject by quoting a passage -from T. Rymer Jones:—“It is, therefore, by no means sufficient -to treat these shells as ordinary objects by simply<span class="pagenum" id="Page_46">46</span> -laying them on a glass slide, so as to see them only from one -or two points of view; they must be carefully examined in -every direction, for such is the diversity of form that nothing -short of this will be at all satisfactory. For this purpose, -they should be attached to the point of a fine needle, so that -they may be turned in any direction, and examined by -reflected light condensed upon them by means of a lens or -side reflector. In many of the thick-shelled species it will -be necessary to grind them down on a hone [see <a href="#CHAPTER_V">Chapter V.</a>] -before the number and arrangement of the internal chambers -is discernible; and in order to investigate satisfactorily the -minutiæ of their structure, a variety of sections, made in -various ways, is indispensable.”</p> - -<p>Plants afford an almost inexhaustible treasury for the -microscope, and many of them show their beauties best when -mounted dry. When any of these also are to be mounted, -care must be taken that they are thoroughly dry, otherwise -the damp will certainly arise in the cell, and injure the -object; and it may be here mentioned that long after a leaf -has every appearance of dryness, the interior is still damp, -and no way can be recommended of getting rid of this by -any quicker process than that effected by keeping them in a -warm room, as many leaves, &c., are utterly spoiled by using -a hot iron or other contrivance. The safest way is to press -them gently betwixt blotting-paper, which may be removed -and dried at short intervals; and though this may appear a -tedious operation, it is a <em>safe</em> one.</p> - -<p>On the surface of the leaves, hairs and scales of various -and very beautiful forms are found, most of which display -their beauties best when removed from the leaf, and used with -the polarizer. These will be noticed in another place; but -a portion of the leaf should always be prepared in its natural -form, to show the arrangement of the hair or scales upon it; -which must almost invariably be mounted dry when used for -this purpose. Many of them require very delicate handling. -The <em>epidermis</em>, or, as it is by some termed, the <em>cuticle</em>, is -the outer skin which lies upon the surface of the leaves and<span class="pagenum" id="Page_47">47</span> -other parts of most plants. This is composed of cells closely -connected, often bearing the appearance of a rude network. -In many plants, by scraping up the surface of the leaf, a -thin coating is detached, which may be torn off by taking -hold of it with the forceps. The piece may then be washed -and floated upon a glass slide, where, on drying, it will be -firmly fixed, and may usually be mounted dry. Amongst -the most beautiful and easily prepared of these may be -mentioned the petal of the geranium, the cells of which are -well defined and amongst the most interesting.</p> - -<p>Closely connected with the leaves are the <span class="smcap smaller">ANTHERS</span> and -<span class="smcap smaller">POLLEN</span>, of which a great number are beautiful and interesting -subjects for the microscopist.</p> - -<p>The mallow tribe will furnish some exquisite objects, -bearing the appearance of masses of costly jewels. These -are usually dried with pressure, but the natural form -may be more accurately preserved by allowing them to -dry as they are taken from the flower, with no interference -except thoroughly protecting them from all dust. Sometimes -the anther is divided, so that the cell required to -receive them may be of as little depth as possible. The -common mallow is a beautiful object, but I think the -lavatera is a better, as it shows the pollen chambers well, -when dried unpressed. The pollen is often set alone, and is -well worth the trouble, as it then admits of more close examination. -Often it is convenient to have the <em>anther and -pollen</em> as seen in nature on one slide, and the <em>pollen</em> alone -upon another. The former should be taken from the -flowers before their full development is attained, as if overgrown -they lose much of their beauty. Some pollens are -naturally so dark that it is necessary to mount them in -Canada balsam or fluid, as described in other places; but -they are better mounted dry when they are not too opaque.</p> - -<p>Here, too, we may also mention the <span class="smcap smaller">SEEDS</span> of many plants -as most interesting, and some of them very beautiful, objects, -requiring for the greater part but a low power to show -them. Most of these are to be mounted dry, as opaque<span class="pagenum" id="Page_48">48</span> -objects, in cells suited to them, but some are best seen in -balsam, and will be mentioned in <a href="#CHAPTER_III">Chapter III.</a></p> - -<p>The <span class="smcap">Corallines</span>, many of which are found on almost every -coast, afford some very valuable objects for the microscope. -They must be well washed when first procured, to get rid of -all the salts in the sea-water, dried and mounted in cells deep -enough to protect them from all danger of pressure, as some -of them are exceedingly fragile. The white ivory appearance -which some of them present is given to them by an -even covering of carbonate of lime; and should it be desired -to examine the structure of these more closely, it may be -accomplished by keeping them for some time in vinegar -or dilute muriatic acid, which will remove the lime and allow -of the substance being sliced in the same way as other Algæ. -(“Micrographic Dictionary,” p. 183.)</p> - -<p><span class="smcap">The Scales of Insects.</span>—The fine dust upon the wings -of moths and butterflies, which is so readily removed when -handled carelessly, is what is generally called <em>scales</em>. To -these the wing owes the magnificent colours which so -often are seen upon it; every particle being what may be -termed a distinct flat feather. How these are placed (somewhat -like tiles upon a roof) may be easily seen in the wing -of any butterfly, a few being removed to aid the investigation. -The form of them is usually that of the -“battledore” with which the common game is played, but -the handle or base of the scale is often short, and the broad -part varies in proportionate length and breadth in different -specimens. The markings upon these also vary, some being -mostly composed of lines running from the base to the apex, -others reminding us of network—bead-like spots only are -seen in some—indeed, almost endless changes are found -amongst them. These scales are not confined to butterflies -and moths, nor indeed to the <em>wings</em> of insects. The different -gnats supply some most beautiful specimens, not only from -the wings, but also from the proboscis, &c.; whilst from -still more minute insects, as the podura, scales are taken -which were at one time esteemed as a most delicate test.<span class="pagenum" id="Page_49">49</span> -The gorgeous colours which the diamond beetles also show -when under the microscope are produced by light reflected -from minute scales with which the insects are covered.</p> - -<p>In mounting these objects for the microscope it is well to -have the part of the insect from which the scales are usually -taken as a separate slide, so that the natural arrangement -of them may be seen. This is easily accomplished with -the wings of butterflies, gnats, &c.; as they require no -extraordinary care. In mounting the <em>scales</em> they may be -placed upon slides, by passing the wings over the surface, -or by gently scraping the wing upon the slide, when they -must be covered with the thin glass. Of course, the extreme -tenuity of these objects does away with the necessity of any -cell excepting that formed by the gold-size or other cement -used to attach the cover. The scales of the podura should -be placed upon the slide in a somewhat different manner. -This insect is without wings, and is no longer than the -common flea. It is often found amongst the sawdust -in wine-cellars, continually leaping about by the aid of -its tail, which is bent underneath its body. Dr. Carpenter -says:—“Poduræ may be obtained by sprinkling a little oatmeal -on a piece of black paper near their haunts; and after -leaving it there for a few hours, removing it carefully -to a large glazed basin, so that, when they leap from -the paper (as they will when brought to the light), they may -fall into the basin, and may thus separate themselves from -the meal. The best way of obtaining their scales, is to -confine several of them together beneath a wine glass -inverted upon a piece of fine smooth paper; for the scales -will become detached by their leaps against the glass, and -will fall upon the paper.” These scales are removed to the -slide, and mounted as those from the gnats, &c. When the -podura has been caught without the aid of the meal, it may -be placed upon the slide, under a test-tube, or by any other -mode of confinement, and thus save the trouble of transfer -from the paper before mentioned. Another method is to -seize the insect by the leg with the forceps and drag it across<span class="pagenum" id="Page_50">50</span> -the slide, when a sufficient quantity of scales will probably -be left upon it.</p> - -<p>These scales are usually mounted “dry;” but Hogg -recommends the use of Canada balsam (<a href="#CHAPTER_III">Chapter III.</a>) as -rendering their structure more definite when illuminated -with Wenham’s parabolic reflector. Some advise other -methods, which will be mentioned in <a href="#CHAPTER_IV">Chapter IV.</a> As most -<em>insects</em> when undissected are mounted in Canada balsam, -the different modes of treatment which they require will be -stated in another place.</p> - -<p>In mounting blood of any kind to show the corpuscles, -or, as they are often called, <em>globules</em>, which are round or -oval discs, it is but necessary to cover the slide on the spot -required with a coating as thin as possible and allow it to -dry before covering with the thin glass. There is a slight -contraction in the globules when dried, but not enough to -injure them for the microscope. The shape of these varies -in different classes of animals, but the size varies much -more, some being many times as large as others.—Some -of the <em>larvæ skins</em> are beautiful objects; but, like many -sections of animal and other fragile matter, are difficult to -extend upon the slide. This difficulty is easily overcome -by floating the thin object in clear water, immersing the -slide and when the object is evenly spread gently lifting it. -Allow it then to dry by slightly raising one end of the slide -to aid the drainage, and cover with the thin glass as other objects. -The tails and fins of many small fish may be mounted -in a similar manner, and are well worth the trouble.</p> - -<p>A few objects which are best shown by mounting <em>dry</em> -may be here mentioned as a slight guide to the beginner, -though some of them have been before noticed;—many -of the Foraminifera as elsewhere described. Some <em>crystals</em> -are soluble in almost any fluid or balsam, and should be -mounted <em>dry</em>; a few, however, deliquesce or effloresce, which -renders them worthless as microscopic objects.</p> - -<p>The wings of butterflies and gnats, as before noticed, -afford many specimens wherewith to supply the cabinet<span class="pagenum" id="Page_51">51</span> -of the young student. A great variety also may be found -amongst the ferns; indeed, these alone will afford the -student occupation for a long time. On the under-side -of the leaves are the reservoirs for the “spores,” which in -many instances somewhat resemble green velvet, and are -arranged in stripes, round masses, and other forms. The -spores are usually covered with a thin skin termed the -<i xml:lang="la" lang="la">indusium</i>, which is curiously marked in some specimens, -often very like pollen-grains. The manner in which -these spores with all their accompaniments are arranged, -their changes and developments afford almost endless subjects -for study; different ferns presenting us with many -variations in this respect totally invisible without the aid -of the microscope. The hymenophyllums (of which two -only belong to England) are particularly interesting, and the -structure of the leaves when dried makes them beautiful -objects, often requiring no balsam to aid their transparency. -Portions of the <em>fronds</em> of ferns should be mounted as -opaque objects, after having been dried between blotting -paper, when they are not injured by pressure; but care must -be taken to gather them at the right time, as they do not -show their beauty before they are ripe, and if over-ripe the -arrangement of the spores, &c., is altered. The spores -may be mounted as separate objects in the same manner -as pollen, before-mentioned, and are exquisitely beautiful -when viewed with a tolerably high power. The number of -foreign ferns now cultivated in this country has greatly -widened the field for research in this direction; and it may -also be mentioned that the under-sides of many are found to -be covered with “scales” of very beautiful forms. A small -piece of the frond of one of these may be mounted in its -natural state, but the removal of the “scales” for examination -by polarized light will be described in another -place. The mosses also are quite a little world, requiring -but a low power to show their beauties. The leaves are of -various forms, some of which resemble beautiful net-work; -the “urns” or reservoirs for the spores, however, are perhaps<span class="pagenum" id="Page_52">52</span> -the most interesting parts of these objects, as also of -the “liverworts” which are closely allied to the mosses. -These “urns” are generally covered by lids, which fall off -when the fruit is ripe. At this period they are well fitted -for the microscope. The common screw-moss may be found -in great abundance, and shows this denudation of the spores -very perfectly. Many of these may be easily dried without -much injury, but they should also be examined in their -natural state.</p> - -<p>The student should not omit from his cabinet a leaf of -the nettle and the allied foreign species, the mystery of -which the microscope will make plain. The hairs or stings -may also be removed, and viewed with a higher power than -when on the leaf, being so transparent as to require no -balsam or other preservative.</p> - -<p>There are few more interesting objects than the <i xml:lang="la" lang="la">raphides</i> -or <em>plant-crystals</em>. These are far from being rare, but in -some plants they are very minute, and consequently require -care in the mounting, as well as a high magnifying power -to render them visible; in others they are so large that -about twenty-five of them placed point to point would reach -one inch. Some of these crystals are long and comparatively -very thin, which suggested the name (<i xml:lang="la" lang="la">raphis</i>, a needle); -others are star-like, with long and slender rays; while -others again are of a somewhat similar form, each ray being -solid and short. If the stem of rhubarb, or almost any of -the hyacinth tribe, be bruised, so that the “juice” may flow -upon the slide, in all probability some of these crystals will -be found in the fluid. To obtain them clean, they must be -freed from all vegetable matter by maceration. After this -they must be thoroughly washed and mounted “dry.” -They are also good <em>polarizing</em> objects, giving brilliant -colours; but when used for this purpose they must be -mounted as described in <a href="#CHAPTER_III">Chapter III.</a> A few plants which -contain them may be mentioned here. The Cactaceæ are -very prolific; the orchids, geraniums, tulips, and the outer -coating of the onion, furnish the more unusual forms.</p> - -<p><span class="pagenum" id="Page_53">53</span> -The Fungi are generally looked upon as a very difficult -class of objects to deal with, but amongst them some of the -most available may be found. The forms of many are very -beautiful, but are so minute as to require a high magnifying -power to show them. The mould which forms on -many substances is a fungus, and in some cases may be dried -and preserved in its natural state. A friend of mine brought -me a rose-bush completely covered with a white blight. -This was found to be a fungus, which required a high magnifying -power to show it. Being a very interesting object, -it was desirable to preserve it, and this was perfectly -effected without injury to the form by simply drying the -leaf in a room usually occupied. Amongst the fungi are -many objects well worth looking for, one of which is the -<i xml:lang="la" lang="la">Diachæa elegans</i>. This, the only species, says the “Micrographic -Dictionary,” is found in England upon the living -leaves of the lily-of-the-valley, &c. These little plants grow -in masses, reminding one of mould, to a height of a quarter -of an inch, and each “stem” is covered with a sheath, in -shape somewhat like an elongated thimble. When ripe the -sheath falls off and reveals the same shaped column, made -up of beautifully fine net-work, with the spores lying here -and there. This dries well, and is a good object for the -middle powers. Amongst the fungi the blights of wheat -and of other articles of food may be included. Many of them -may be mounted “dry;” others, however, cannot be well -preserved except in liquids, and will be referred to in <a href="#CHAPTER_IV">Chapter -IV.</a> Amongst the zoophytes and sea-mats, commonly -called “sea-weeds,” may be found many very interesting -objects to be mounted “dry.” When this mode of preservation -is used, it is necessary that all the sea-salt be -thoroughly washed from them. As they are, however, most -frequently mounted in balsam or liquid, they will be more -fully noticed in other places.</p> - -<p>The <em>scales of fishes</em> are generally mounted “dry” when -used as ordinary objects; but for polarized light, balsam or -liquid must be used, as noticed in <a href="#CHAPTER_III">Chapter III.</a> The variety<span class="pagenum" id="Page_54">54</span> -and beauty of these are quite surprising to the novice. -It is also very interesting to procure the skin of the fish -when possible, and mount it on a separate slide to show -how the scales are arranged. The sole is one of the most -unusual forms, the projecting end of each scale being covered -with spines, which radiate from a common centre, while -those at the extremity are carried out somewhat resembling -the rays of a star. One of the skates has a spine projecting -from the centre of each scale, which is a very curious -opaque object, especially when the skin is mounted in the -manner described. The perch, roach, minnow, and others -of the common fishes give the student good objects for his -cabinet, and may be procured without difficulty.</p> - -<p>Insects which are very transparent, or have the -“metallic lustre” with which any medium would interfere, -are mounted “dry.” The diamond-beetle, before mentioned, -is a splendid example of this; the back is generally used, -but the legs, showing the curious feet, are very interesting -objects. Indeed, amongst the legs and feet of insects there -is a wide field of interest. When they are of a “horny” -nature, it is best to dry them in any form preferred, but to -use no pressure; when, however, they are wanted flat, so as -to show the feet, &c., extended, they must be dried with -a gentle pressure betwixt blotting-paper if possible. But -this will be treated more fully in <a href="#CHAPTER_III">Chapter III.</a></p> - -<p>The <em>eyes of insects</em> are sometimes allowed to dry in their -natural shape, and mounted as opaque objects; but -generally they are used as transparencies in balsam or -liquid, so the description of the treatment which they -require will be deferred to <a href="#CHAPTER_III">Chapter III.</a></p> - -<p>Hairs, when not too dark, are sometimes transparent -enough when mounted dry, but are usually mounted in -balsam. These also will be more fully noticed in another -place.</p> - -<p>These are a few of the objects which are often mounted -dry, but some of them should be shown in balsam or liquid -also, and there is much difference of opinion as to the best<span class="pagenum" id="Page_55">55</span> -way of preserving others. This, however, is explained by -the transparency which the balsam gives interfering with -one property of the object and yet developing another -which would have remained invisible if preserved dry. The -only method of overcoming this difficulty is to keep the -object mounted in both ways, which is comparatively little -trouble.</p> - -<p>I may here mention that many prefer the lieberkuhn -for the illumination of opaque objects; and a good background -is gained by putting upon the under side of the -slide, immediately beneath the object, a spot of black -varnish, which does not interfere materially with the light.</p> - -<hr /> - -<p><span class="pagenum" id="Page_56">56</span></p> - -<div class="chapter"> -<h2 id="CHAPTER_III" class="vspace"><span class="gesperrt">CHAPTER III</span>.<br /> - -<span class="subhead">MOUNTING IN CANADA BALSAM.</span></h2> -</div> - -<p class="in0"><span class="firstword">The</span> nature and use of this substance has been before spoken -of, so the method of working with it may be at once described.</p> - -<p>Perfect dryness of the objects is, if possible, more necessary -in this mode of mounting than any other, as dampness -remaining in the object will assuredly cause a cloudiness to -make its appearance in a short time after it is fixed. Where -pressure does not injure the specimens, they are most successfully -treated when first dried betwixt the leaves of a -book, or in any other way which may prove most convenient, -as noticed in <a href="#CHAPTER_II">Chapter II.</a></p> - -<p>Before describing the methods of proceeding with any -particular objects, general rules may be given which should -be observed in order to succeed in this branch of mounting.</p> - -<p>As the object is to be thoroughly immersed in the balsam, -it is evident that when it has once been covered, so -it must remain, unless we again free it by a process hereafter -mentioned, which is very troublesome; and on this -account there must be nothing whatever in the balsam -except the object. The inexperienced may think this an -unnecessary caution; but the greatest difficulty he will meet -with is to get rid of minute bubbles of air, perhaps invisible -to the naked eye, which appear like small globules when -under the microscope, and render the slide unsightly, or even -worthless. Ten objects out of eleven contain air, or at least -are full of minute holes which are necessarily filled with it; -so that if they should be immersed in any liquid of thick -consistency, these cells of air would be imprisoned, and -become <em>bubbles</em>. The air, then, must be got rid of, and this<span class="pagenum" id="Page_57">57</span> -is usually accomplished by soaking for some time in turpentine, -the period required differing according to the nature of -the object. In some cases, the turpentine acts upon the -colour, or even removes it altogether, so that it must be -watched carefully. Often, however, this is an advantage, as -where the structure alone is wanted, the removal of the -colouring matter renders it more transparent. There are -objects, however, which retain the air with such tenacity -that soaking alone will not remove it. If these will bear -heat without being injured, they <em>may</em> be boiled in turpentine, -or even in balsam, when the air will be partly or totally -expelled. But where heat is objectionable, they must be -immersed in the turpentine, and so submitted to the action -of the air-pump. Even with this aid, sometimes days are -required to accomplish it perfectly, during which time the -air should be exhausted at intervals of five or six hours, if -convenient, and the objects turned over now and then.</p> - -<p>Sometimes the objects are so minute that it is impossible -to submit them to any soaking, and in this case they must -be laid upon the slide at once, and the turpentine applied to -them there. But it must not be forgotten that there are -some few which are much better mounted in such a way -that the balsam may thoroughly surround, and yet not -<em>penetrate</em>, the substance more than necessary. Sections of -teeth are amongst these, which will be noticed in another -place, and some insects (see Dr. Carpenter) when required -to show the “ramifications of the tracheæ.”</p> - -<p>Having freed the object, then, from these two enemies—dampness -and air—we must proceed to mount it.</p> - -<p>The slide must first be cleaned; then on the centre a -quantity of balsam must be placed with a bluntly-pointed -glass rod, according to the size of the object about to be -mounted. To this a slight heat must be applied, which will -cause any bubbles to rise from the surface of the slide, so -that they may be readily removed with a needle. The object -should be freed from all air by steeping in turpentine, as -before described, and then from superfluous liquid by a<span class="pagenum" id="Page_58">58</span> -short drainage, and carefully laid <em>upon</em>, or where it is practicable -thrust <em>into</em>, the balsam, prepared on the slide as -above. In the former case, or where the balsam has not -totally covered the object, a small quantity must be taken, -warmed, and dropped upon it, and any bubbles removed by -the needle as before. To cover this, the thin glass must be -warmed, and beginning at one side, allowed to fall upon the -balsam, driving a small “wave” before it, and thus expelling -any bubbles which may remain. This is quite as safely -performed (if not more so) by making a solution of balsam -in turpentine of the consistency of thick varnish. The thin -glass cover may be slightly coated with this, and will then -be much less liable to imprison any air, which frequently -happens when the cover is dry. Bubbles, however, will -sometimes make their appearance in spite of all care; but -when the object is comparatively strong, they may be -removed by keeping the slide rather warm, and <em>working</em> the -cover a little, so as to press them to one side, when they -should be immediately removed with a needle point, otherwise -they are again drawn under.</p> - -<p>Where the slide requires keeping warm for any length of -time, a <em>hot-water bath</em> is sometimes made use of, which is -simply a flat tin, or other metal case, with a mouth at the -side, that when the hot water is introduced it may be -closed up, and so retain its warmth for a long time. In -working, the slide is laid upon it, and so admits of longer -operations, when required, without growing cold. Sometimes -a spirit-lamp is placed under it to keep up an equal heat -through excessively long processes. Where the time required, -however, is but short, a thick brass plate is sometimes used -(see <a href="#CHAPTER_I">Chapter I.</a>), which is heated to any degree that is -required, and the slide placed upon it.</p> - -<p>Some objects, which are so thin that they are usually -<em>floated</em> upon the slide, as before stated, require no steeping in -turpentine or other liquid. These are best mounted by -covering with a little <em>diluted</em> balsam, and after this -has had time to penetrate the substance, ordinary balsam<span class="pagenum" id="Page_59">59</span> -is laid upon it, and the slide finished in the usual -manner.</p> - -<p>I have stated that the balsam is usually applied to the -slide and objects with a “bluntly-pointed glass rod;” but -for the purpose of drawing the balsam from the bottle, and -conveying it to the desired place, Dr. Carpenter uses a glass -syringe with a <em>free</em> opening. These are his instructions:—“This -(the syringe) is most readily filled with balsam, in -the first instance, by drawing out the piston, and pouring in -balsam previously rendered more liquid by gentle warmth; -and nothing else is required to enable the operator at any -time to expel precisely the amount of balsam he may require, -than to warm the point of the syringe, if the balsam should -have hardened in it, and to apply a very gentle heat to the -syringe generally, if the piston should not then be readily -pressed down. When a number of balsam objects are being -mounted at one time, the advantage of this plan in regard -to facility and cleanliness (no superfluous balsam being -deposited on the slide) will make itself sensibly felt.”</p> - -<p>When the “mounting” is thus far accomplished, the -outer “wall” of balsam may be roughly removed after a -few hours have elapsed; but great care is necessary lest the -cover be moved or interfered with in any way. In this -state it may be left for the final cleansing until the balsam -becomes hard, which takes place sooner or later, according -to the degree of warmth it has been subjected to. A -mantel-piece, or some place about equal to it in temperature, -is the best suited to this purpose; and when the requisite -hardness is attained, it may be proceeded with as follows:—With -a pointed knife the balsam must be scraped away, -taking care that the thin glass be not cracked by the point -getting <em>under</em> it. If used carefully, the knife will render the -slide almost clean; but any minute portions which still -adhere to the glass must be rubbed with linen dipped in -turpentine or spirit. If the balsam is not very hard, these -small fragments are readily removed by folding a piece of -paper tightly in a triangular form with many folds, and<span class="pagenum" id="Page_60">60</span> -damping the point with which the glass is rubbed. As the -paper becomes worn with the friction, the balsam will be -carried off with it. In some cases I have found this simple -expedient very useful.</p> - -<p>Sometimes the object to be mounted is of such a thickness -as to require a cell. For this purpose glass rings are used -(as described in <a href="#CHAPTER_IV">Chapter IV.</a>), and filled with balsam. The -best mode of doing this is thus described by Mr. T. S. -Ralph in the <cite>Microscopic Journal</cite>:—“The question was -asked me when I was in England, if I knew how to fill a -cell with Canada balsam and leave behind no air-bubbles? -I replied in the negative; but now I can state how to accomplish -this. Fill the cell with clear spirit of turpentine, -place the specimen in it, have ready some balsam just -fluid enough to flow out of the bottle when warmed by the -hand; pour this on the object at one end, and, gradually -inclining the slide, allow the spirit of turpentine to flow out -on the opposite side of the cell till it is full of balsam; then -take up the cover, and carefully place upon it a small -streak of Canada balsam from one end to the other. This, -if laid on the cell with one edge first, and then gradually -lowered until it lies flat, will drive all the air before it, and -prevent any bubbles from being included in the cell. It can -be easily put on so neatly as to require no cleaning when -dry. If the cover is pressed down too rapidly, the balsam -will flow over it, and require to be cleaned off when -hardened, for it cannot be done safely while fluid at the -edges.”</p> - -<p>Sometimes with every care bubbles are enclosed in the -balsam, injuring objects which are perhaps rare and valuable. -The whole slide must then be immersed in turpentine until -the cover is removed by the solution of the balsam; and the -object must be cleansed by a similar steeping. It may then -be remounted as if new in the manner before described.</p> - -<p>The balsam and chloroform described in <a href="#CHAPTER_I">Chapter I.</a> is -thus used; and where the object is thin, the mounting is -very easily accomplished. When the object is laid upon the<span class="pagenum" id="Page_61">61</span> -slide with a piece of glass upon it, and the balsam and -chloroform placed at the edge of the cover, the mixture will -gradually flow into the space betwixt the glasses until the -object is surrounded by it, and the unoccupied portion filled. -The chloroform will evaporate so quickly that the outer edge -will become hard in a very short time, when it may be -cleaned in the ordinary way. Sometimes the balsam is -dissolved in the chloroform without being first hardened; -but this is only to render it more fluid, and so give the -operator less chance of leaving bubbles in the finished slide, -as the thicker the medium is, the more difficult is it to get -rid of these intruders.</p> - -<p>It has been before mentioned that some have objected to -chloroform and balsam, believing that it became <em>clouded</em> -after a certain time. Perhaps this may be accounted for -in part by the fact that almost all objects have a certain -amount of dampness in them. Others are kept in some -preservative liquid until the time of mounting, and these -liquids generally contain certain salts (<a href="#CHAPTER_IV">Chapter IV.</a>). If -this dampness, as well as all traces of these salts, however -small, are not totally removed—the former by drying, the -latter by repeated washings—the addition of chloroform -will render the balsam much more liable to the cloudiness -than when balsam alone was used, as before mentioned.</p> - -<p>This mode of employing the balsam, however, will not be -always applicable, as <em>chloroform</em> acts upon some substances -which balsam <em>alone</em> does not. Some salts are even soluble in -it, the crystals disappearing after a few days or weeks, whereas -in the balsam alone they are quite permanent. Experience -is the only guide in some cases, whilst in others a little -forethought will be all that is required.</p> - -<p>The particular methods used for certain objects may be now -entered upon. Many of the Diatomaceæ and fossil Infusoria, -as they are sometimes termed, are mounted dry, and cleaned -in the way described in <a href="#CHAPTER_II">Chapter II.</a> Others are almost -always placed in balsam, except where they are intended to -be used with the lieberkuhn and dark background, by which<span class="pagenum" id="Page_62">62</span> -means some of them are rendered exquisitely beautiful. The -usual way of mounting them in balsam is as follows:—Take -a drop of the water containing them, place it upon the slide, -and evaporate over the lamp, whilst with a needle they may -be dispersed over any space desired. When they are thoroughly -dry, drop a little balsam on one side, and exclude -the bubbles. The slide may then be warmed to such a -degree that the balsam, by lifting the glass at one end, will -be carried over the specimens, which may then be covered -with thin glass, made warm as before described. Where the -objects are quite dry, and loose upon the glass, it requires -great care in placing the cover upon them, otherwise they -are forced to one edge, or altogether from under it, in the -wave of the balsam. For this reason, Professor Williamson -adds a few drops of gum-water to the last washing, which -causes them to adhere sufficiently to the glass to prevent -any such mishap.</p> - -<p>Mr. T. G. Rylands’ method differs in some degree from -the above, and is, to use his own words, as follows:—Thick -balsam is preferable, and the burnt covers (see <a href="#CHAPTER_II">Chapter II.</a>) -to be mounted are laid in a convenient position with the -diatoms upwards. The slides required having been carefully -cleaned and marked on the under side with a ring of -ink, by the aid of a turntable about half an inch in diameter -to point out the centre, a drop of benzole is applied by a -large pin to the diatoms on the cover, so as to exclude the -air from the valves and frustules. The slide is then held -over the lamp, and when warm, a sufficiently large drop of -balsam is put upon it, and heated until it begins to steam. -If small bubbles appear, a puff of breath removes them. -The slide being held slightly inclined from the operator, and -the drop of balsam becoming convex at its lower edge, the -cover is brought in contact with it at that point, gradually -laid down, pressed with the forceps, and brought to its -central position. When cool the superfluous balsam (if -any) is removed with a heated knife-blade, the slide cleaned -with a little turpentine, and finished by washing in a hand-basin<span class="pagenum" id="Page_63">63</span> -with soap and water. In this process there is no -delay if the balsam be sufficiently thick, as the slide may be -cleaned off almost before it is cold.</p> - -<p>It is now well known that from common chalk it is an -easy matter to obtain interesting specimens of Foraminifera. -Scrape a small quantity of chalk from the mass and shake -it in water; leave this a few minutes, pour the water away -and add a fresh quantity, shake up as before, and repeat -two or three times. Take a little of the residue, and spread -it upon the slide, and when quite dry add a little turpentine. -When viewed with a power of two hundred and fifty diameters -this will generally show the organisms very well. -If it is desired to preserve the slides, they may be then -mounted in Canada balsam. Mr. Guyon, in “Recreative -Science,” observes that the accumulation of the powder, by -the action of the rain or exposure to the atmospheric action, -at the foot or any projection of the chalk cliffs, will afford -us better specimens than that which is “scraped,” as the -organisms are less broken in the former.</p> - -<p>When the Foraminifera are of a larger size, though transparent -enough to be mounted in balsam, the air must be -first expelled from the interior, otherwise the objects will be -altogether unsatisfactory. To accomplish this they must -be immersed in turpentine and submitted to the action of -the air-pump. So difficult is it to get rid of this enemy -that it is often necessary to employ three or four exhaustions, -leaving them for some time under each. When all -air has given place to the turpentine, they must be mounted -in the ordinary way.</p> - -<p>Of all objects which are commonly met with, few are such -general favourites as the <span class="smcap">Polycystinæ</span>, and deservedly so. -Their forms are most beautiful, and often peculiar—stars -varying in design, others closely resembling crowns; the -<i xml:lang="la" lang="la">Astromma Aristotelis</i> like a cross, and many whose shapes -no words could describe. The greater part, perhaps, of -those which are usually sold, is from the rocky parts of -Bermuda; but they are also found in Sicily, some parts of<span class="pagenum" id="Page_64">64</span> -Africa and America. They are usually mounted in balsam, -but are equally beautiful mounted “dry” and used with the -lieberkuhn. They require as much care in cleaning as the -Diatomaceæ, but the process is a different one. Sometimes -this is effected by simply washing until they are freed from -all extraneous matter, but this is seldom as effectual as it -should be. In the <cite>Microscopic Journal</cite> Mr. Furlong gives -the following method of treatment as the best he <span class="locked">knew:—</span></p> - -<p>Procure—</p> - -<div class="in2"> -<p class="hang">A large glass vessel with 3 or 4 quarts of water.</p> - -<p class="hang">New tin saucepan holding 1 pint.</p> - -<p class="hang">2 thin precipitating glasses holding 10 oz. each.</p> -</div> - -<p class="in0">Take 3 oz. of dry “Barbadoes earth” (lumps are best), and -break into rather small fragments. Put 3 or 4 oz. of common -washing soda into the tin and half fill it with water. -Boil strongly, and having thrown in the earth, boil it for -half an hour. Pour nine-tenths of this into the large glass -vessel, and gently crush the remaining lumps with a soft -bristle brush. Add soda and water as before, and boil -again; then pour off the liquid into the large vessel, and -repeat until nothing of value remains. Stir the large vessel -with an ivory spatula, let it stand for three minutes, and pour -gently off nine-tenths of the contents, when the shells will -be left, partially freed only, like sand.</p> - -<p><span class="smcap">2nd Process.</span>—Put common washing soda and water into -the tin as before, and having placed the shells therein, boil -for an hour. Transfer to the large vessel as before, and -after allowing it to stand for one minute pour off. Each -washing brings off a kind of “flock,” which seems to be -skins.</p> - -<p><span class="smcap">3rd Process.</span>—Put the shells in precipitating glass and -drain off the water until not more than ½ oz. remains. Add -half a teaspoonful of bicarbonate of soda, dissolve, and then -pour in gently 1 oz. of strong sulphuric acid. This liberates -the “flock,” &c., and leaves the shells beautifully transparent. -Wash well now with water to get rid of all salts and other -soluble matter.</p> - -<p><span class="pagenum" id="Page_65">65</span> -Some of the large shells are destroyed by this method, -but none that are fit for microscopic use. An oblique light -shows these objects best.</p> - -<p>These are sometimes treated in the manner described in -<a href="#CHAPTER_II">Chapter II.</a> where the diatoms are spoken of, but many -forms are liable to be injured by this severe process.</p> - -<p>It has been before stated that some of the zoophytes may -be mounted dry, and others examined as opaque or transparent -objects according to their substance. They are very -interesting when examined in the trough whilst living, but -to preserve many of them for future examination they must -be mounted in some preservative medium. Sometimes this -may be one of the liquids mentioned in <a href="#CHAPTER_IV">Chapter IV.</a>, but -if possible they should be kept in balsam, as there is less -danger of injury by accident to this kind of slide. This -method of mounting presents some difficulties, but I think -that all agree as to the trustworthiness of Dr. Golding Bird’s -information on the subject, which appeared in the <cite>Microscopic -Journal</cite>. Of this, space forbids me to give more than -a condensed account, but I hope to omit nothing of moment -to the reader for whom these pages are written.</p> - -<p>After stating that there are few who are not familiar -with these exquisite forms, and have not regretted the great -loss of beauty they sustain in dying, he informs us that -from their so obstinately retaining air in the cells and tubes -when dried, it is hardly practicable to get rid of it; and -they also shrivel up very seriously in the process of drying. -The following plan, however, he has found almost faultless -in their preparation.</p> - -<p>To preserve them with extended tentacles, they should be -plunged in cold fresh water, which kills them so quickly -that these are not often retracted. The specimens should -be preserved in spirit until there is leisure to prepare them; -if, however, they have been <em>dried</em>, they should be soaked in -cold water for a day or two before being submitted to the -following <span class="locked">processes:—</span></p> - -<p>1. After selecting perfect specimens of suitable size, immerse<span class="pagenum" id="Page_66">66</span> -them in water heated to about 120° and place them -under the receiver of an air-pump. Slowly exhaust the -air, when bubbles will rise and the water appear to be in a -state of active ebullition. After a few minutes re-admit -the air and again exhaust, repeating the process three or -four times. This will displace the air from most, if not all, -of the class.</p> - -<p>2. Remove the specimens and allow them to drain upon -blotting-paper for a few seconds; then place them in an -earthen vessel fitted with a cover, and previously heated -to about 200°. This heat may be easily got by placing -the vessel for a short time in boiling water, wiping it -immediately before use with a thick cloth. The specimens -are then dropped into this, covered with the lid, -and immediately placed under the receiver of the air-pump, -and the air rapidly exhausted. By this means they -are dried completely, and so quickly that the cells have -no time to wrinkle.</p> - -<p>3. In an hour or two remove them from the air-pump -and drop them into a vessel of perfectly transparent camphine. -This may be quite cold when the horny, tubular -polypidoms, as those of the Sertulariæ, are used; but should -be previously heated to 100° when the calcareous, cellular -Polyzoa are the objects to be preserved. The vessel should -be covered with a watch-glass and placed under the receiver, -the air being exhausted and re-admitted two or three times.</p> - -<p>4. The slide which is to receive the specimen should be -well cleaned and warmed so as to allow the balsam to flow -freely over it. This must be applied in good quantity, -and air-bubbles removed with the needle-point. Take the -polypidom from the camphine, drain it a little, and with -the forceps immerse it fully in the balsam. The glass to -be laid upon it should be warmed and its surface covered -with a thin layer of balsam, and then lowered gradually -upon it, when no bubbles should be imprisoned. A narrow -piece of card-board at each end of the object for the cover -to rest upon, prevents any danger of crushing the specimen.</p> - -<p><span class="pagenum" id="Page_67">67</span> -This mode of mounting polypidoms, &c., seems to give -almost the complete beauty of the fresh specimens. They -are very beautiful objects when viewed with common light, -but much more so when the polarizer is used (in the -manner described a little farther on).</p> - -<p>To the above instructions there can be little to add; but -I may here mention that some young students may not be -possessed of the air-pump, and on this account put aside -all search for those specimens which need little looking for -at the seaside. Many of these, however, though they lose -some beauty by the ordinary mode of drying, will by -steeping for some time in turpentine not only be freed -from the air-bubbles, but suffer so little contraction that -they are a worthy addition to the cabinet.</p> - -<p>Another class of objects is the <i xml:lang="la" lang="la">spicula</i> met with in -sponges, &c. These are often glass-like in appearance and -of various shapes; many are found resembling needles -(whence their name); some from the synapta are anchor-like, -whilst others are star-like and of complex and almost -indescribable combinations. As some of these are composed -of silex and are consequently not injured by the use -of nitric acid, the animal substance may be got rid of by -boiling them in it. Those, however, which are calcareous -must be treated with a strong solution of potash instead; -but whichever way is used, of course they must afterwards -be freed from every trace of residue by careful -washing.</p> - -<p>These spicules may be often found amongst the sand -which generally accumulates at the bottom of the jars in -which sponges are kept by those who deal in them, and -must be picked out with a camel-hair pencil. The specimens -obtained by this means will seldom if ever require -any cleaning process, as they are quite free from animal -matter, &c.</p> - -<p>In the former chapter was noticed those insects or parts -of them which are usually mounted dry. When they are -large and too opaque to admit of the dry treatment, they<span class="pagenum" id="Page_68">68</span> -must be preserved in Canada balsam or fluid. The first of -these may now be considered.</p> - -<p>It may be here mentioned, that with these objects much -heat must not be employed, as it would in some instances -give rise to a cloudiness, and almost invariably injure -them.</p> - -<p>In killing the insect it is necessary not to rub or break -any part of it. This may be performed by placing it -in a small box half filled with fragments of fresh laurel -leaves, by immersion in turpentine or strong spirit, as -also in solutions of various poisonous salts. After which -it may be preserved for sometime in turpentine or other -preservative liquid (<a href="#CHAPTER_IV">Chapter IV.</a>) until required. As an -assistance to the student, I believe that I can do no better -than give him the plan pursued by my friend Mr. Hepworth, -whose specimens are in every way satisfactory; -but when his method is used, the insects must not have been -placed in turpentine for <span class="locked">preservation:—</span></p> - -<p>“After destroying the insects in chloroform or sulphuric -ether (methylated being cheaper), wash them thoroughly in -a wide-necked bottle, half-filled, with two or three waters; -the delicate ones requiring great care. Then immerse -them in liquid potash (or Brandish’s solution, which is -stronger than the usual preparation), and let them remain a -longer or shorter time according to their texture. When -ready to remove, put one by one into a small saucer of clear -water, and with a camel-hair pencil in each hand press -them flat to the bottom, holding the head and thorax with -the left-hand brush, and apply pressure with the other from -above, downwards, giving the brush a rolling motion, which -generally expels the contents of the abdomen from the -thorax. A minute roller of pith or cork might be used -instead of the brush. In larger objects, use the end of the -finger to flatten them. Large objects require more frequent -washing, as it is desirable to remove the potash thoroughly, -or crystals are apt to form after mounting. Having placed -them on the slides with thin glass covers, tied down with<span class="pagenum" id="Page_69">69</span> -thread,<a id="FNanchor_C" href="#Footnote_C" class="fnanchor">C</a> dry and immerse them in rectified spirits of turpentine; -place the vessel under the receiver of an air-pump, -and keep it exhausted until the turpentine has taken -the place of the air-bubbles: they are then ready for the -application of the balsam. Larger objects may often with -advantage be transferred to a clean slide, as during the -drying there is considerable contraction, and an outline -often remains beyond the margin showing this. When -closely corked they may remain in the spirits two or three -months. As you take them from the bottle, wipe as much -turpentine off as possible before removing the thread, and -when untied carefully wipe again, placing the finger on one -end of the cover whilst you wipe the other, and vice versâ. -By this means you remove as much turpentine from under the -cover as is necessary; then drop the balsam, thinned with -chloroform (see <a href="#CHAPTER_I">Chapter I.</a>), upon the slide, letting the fluid -touch the cover, when it will be taken in between the -surfaces by capillary attraction; and after pressing the -cover down it may be left to dry, or you may hold the -slide over a spirit-lamp for a few seconds before pressing -down the cover. If heat is not applied, they are much longer -in drying but are more transparent. If made too hot the -boiling disarranges the objects, and if carried too far will -leave only the resin of the balsam, rendering it so brittle -that the cover is apt to fly off by a fall or any jar producing -sufficient percussion. Never lift the cover up, if possible, -during the operation, as there is danger of admitting air. -A few bubbles may appear immediately after mounting, but -generally subside after a few hours, being only the chloroform -or turpentine in a state of vapour, which becomes -condensed.”</p> - -<div class="footnote"> - -<p><a id="Footnote_C" href="#FNanchor_C" class="fnanchor">C</a> This applies to the more delicate ones, which will not bear -transferring after being once spread out and dried.</p></div> - -<p>This method of preparing and mounting insects I can -strongly recommend as giving first-rate results; but where the -specimens are small they seldom need the soaking in caustic<span class="pagenum" id="Page_70">70</span> -potash which larger ones must have. It is only necessary -to leave them awhile in turpentine, especially when they have -been first dried with gentle pressure between two glasses, -and then mount with balsam in the ordinary way.</p> - -<p>Amongst the insect tribes there is abundant employment, -especially for the lower powers of the microscope. But if -the deeper wonders and beauties of the animal economy are -to be sought out and studied, it is desirable that the various -parts should be set separately, in order that they may -receive a more undivided attention, as well as to render -them capable of being dealt with under the higher powers. -We will, therefore, briefly consider the treatment which the -different portions require.</p> - -<p>The eyes of the butterflies, and indeed of almost all insects, -afford materials for a study which is complete in itself. -When examined with a tolerably high power, instead of -finding each eye with an unbroken spherical surface, it is seen -that many are composed of thousands of hexagonal divisions, -each being the outer surface of a separate portion termed -the <i xml:lang="la" lang="la">ocellus</i>. In others these divisions are square; but in all -there is a layer of dark pigment surrounding their lower -parts. The ocelli may be partly removed from the eye, -which will show how their tapering forms are arranged. -But here we have to consider how to place them in balsam -for preservation. The eye being removed from the insect, -and the dark pigment removed by the use of a camel-hair -pencil, must be allowed to remain in turpentine at least -for some days. The turpentine should then be renewed and -the eye well washed in it just before it is to be mounted. -It may then be set in balsam in the same way as any other -object;—but here a difficulty is met with. The eye being -spherical upon the surface required, must necessarily be -“folded” or broken in attempting to flatten it. This difficulty -may be often overcome by cutting a number of slits -round the edges; but some object to this mode of treatment, -and where it is practicable it is much more satisfactory to -mount one in the natural rounded form and another flat.<span class="pagenum" id="Page_71">71</span> -Instead, however, of mounting the organ <em>whole</em>, four or five -slides may be procured from each of the larger ones, as -those of the dragon-fly, &c.</p> - -<p>The <em>antennæ</em> also are often mounted on separate slides, -as being better suited for higher powers and more minute -examination than when connected with the insect. These -two projecting organs, issuing from the head, are jointed, and -moveable at will. They differ very much in form amongst -the various species, and are well worth the attention of the -microscopist. They are usually mounted with the head -attached, and perhaps they are more interesting when thus -seen. Some few are very opaque, to prepare which the -following method has been <span class="locked">advised:—</span></p> - -<p>Bleach the antennæ by soaking in the following solution -for a day or <span class="locked">two:—</span></p> - -<div class="center"><div class="ilb"> -<p class="in0"> -Hydrochloric acid, 10 drops.<br /> -Chlorate of potash, ½ drachm.<br /> -Water, 1 oz.</p> -</div></div> - -<p class="in0">This will render them transparent. Wash well, dry, and -mount in Canada balsam. Instead of the above, a weak -solution of chloride of lime may be used, by which means -the nerves will be well shown. Many, however, are rendered -transparent enough by simply soaking in turpentine for a -longer or shorter time. Where the antennæ, however, are -“plumose,” or feather-like, extreme care is required in -mounting, though the difficulty is not so great as some seem -to think. If they are first dried with gentle pressure, and -then subjected to the action of the air-pump in a small -quantity of turpentine until the air is thoroughly expelled, -they can be easily finished upon the slide, especially when -balsam and chloroform are used.</p> - -<p>Insects supply us with another series of beautiful objects, -viz., the <em>feet</em>.<a id="FNanchor_D" href="#Footnote_D" class="fnanchor">D</a> These are sometimes simply dried and<span class="pagenum" id="Page_72">72</span> -mounted without any medium, as before mentioned; but -most of them are rendered much more fit for examination -by using balsam in their preservation, as it greatly increases -their transparency. The smaller kinds may be dried with -gentle pressure betwixt blotting-paper, and then immersed -for some days in turpentine, without requiring the treatment -with liquor potassæ. This immersion will render them -beautifully transparent, when they may be mounted in -balsam in the usual manner.</p> - -<div class="footnote"> - -<p><a id="Footnote_D" href="#FNanchor_D" class="fnanchor">D</a> See Mr. Hepworth’s interesting articles on the fly’s foot in the -second and third volumes of the <cite>Microscopic Journal</cite>.</p></div> - -<p>It is, however, sometimes found difficult to fix the feet -when <em>expanded</em>, in which state the interest of the object is -greatly increased. Mr. Ralph recommends the following -mode:—“First wash the feet, while the insect is yet alive, -with spirits of wine; then holding it by a pair of forceps -close to the edge of a clean piece of glass, the insect will lay -hold of the upper surface by its foot, then suddenly drop -another small piece of glass over it, so as to retain the foot -expanded, and cut it off with a pair of scissors, tie up -and soak to get rid of air.” Mr. Hepworth says that he -never found any difficulty in expanding the foot on a -drop of water or well-wetted slide, and laying a thin glass -cover over it, tying with thread, drying, and immersing in -turpentine.</p> - -<p>The mouth, also, with its organs, is an interesting object -in many insects. That of the common fly is often made -use of, and is comparatively easy to prepare. By pressing -the head, the tongue (as it is commonly termed) will be forced -to protrude, when it must be secured by the same means as -the foot, and may be subjected to the soaking in turpentine, -and mounted as usual. The honey-bee is, however, very -different in formation, and is well worth another slide; -indeed, even in insects of the same class, the differences are -many and interesting.</p> - -<p>Another worthy object of study is the <em>respiration</em> of -insects, which is effected by tracheæ or hollow tubes, which -generally run through the body in one or more large trunks, -branching out on every side. These terminate at the surface<span class="pagenum" id="Page_73">73</span> -in openings, which are termed <i xml:lang="la" lang="la">spiracles</i>, or breathing -organs. The <i xml:lang="la" lang="la">tracheæ</i> often present the appearance of tubes -constructed by a twisted thread, somewhat resembling the -spiral fibres of some plants. These are very beautiful -objects, and are generally mounted in balsam, for which -reason they are mentioned here; but as they evidently belong -to the “dissecting portion,” they will be fully treated of in -another place.</p> - -<p>Amongst the parasitic insects a great variety of microscopic -subjects will be found. As these are usually small, -they may be killed by immersion in spirits of turpentine; and -if at all opaque, may be allowed to remain in the liquid until -transparent enough, and then mounted in Canada balsam.</p> - -<p>The acarida, or <em>mites</em> and <em>ticks</em>, are well known; none, -perhaps, better than those which are so often found upon -cheese. Flour, sugar, figs, and other eatables, are much -infested by them; whilst the diseases called the <em>itch</em> in man, -and the <em>mange</em> in animals, are produced by creatures -belonging to this tribe. These animals are sometimes -mounted by simply steeping them in turpentine, and proceeding -as with other insects. The “Micrographic Dictionary” -gives the following directions as to mounting <em>parts</em> of -these:—“The parts of the mouth and the legs, upon which -the characters are usually founded, may be best made out by -crushing the animals upon a slide with a thin glass cover, -and washing away the exuding substance with water; sometimes -hot solution of potash is requisite, with the subsequent -addition of acetic acid, and further washing. When afterwards -dried and immersed in Canada balsam, the various -parts become beautifully distinct, and may be permanently -preserved.”</p> - -<p>Feathers of different kinds of birds are usually mounted -in balsam when required to show much of the structure. -This is particularly interesting when the feathers are small, -as they then show the inner substance, or <em>pith</em>, as it may be -termed, with the cells, &c. The “pinnæ,” or soft branches -of the feathers, will be found of various constructions; some<span class="pagenum" id="Page_74">74</span> -possessing hooks along one side, whereby they fasten -themselves to their neighbours; others branching out, with -straight points somewhat resembling the hairs from certain -caterpillars. But, of course, when the metallic-looking -gorgeous colours are all that is required to be shown, and -reflected light used (as with the feathers of the hummingbird, -peacock, &c.), it is much better that they should be -mounted dry, as in <a href="#CHAPTER_II">Chapter II.</a></p> - -<p>The <em>seeds</em> and <em>pollen</em> of plants are most frequently -mounted dry, as mentioned in <a href="#CHAPTER_II">Chapter II.</a>; but the more -transparent of the former, and the darker kinds of the -latter, are perhaps better seen in Canada balsam. There -is nothing particular to be observed in the manipulation, -except that the glass cover must be applied lightly, otherwise -the grains may be crushed. There are some objects which -cannot be shown in a perfect manner when mounted <em>dry</em>, but -when immersed in balsam become so very transparent that -they are almost useless. To avoid this, it has been recommended -to stain the objects any colour that may be convenient, -and afterwards mount in balsam in the ordinary -manner.</p> - -<p>Most objects intended for the polariscope may be mounted -in Canada balsam; but there are some exceptions to this. -Many of the salts are soluble in this medium, or their -forms so injured by it, that glycerine or oil has to be used -(see <a href="#CHAPTER_IV">Chapter IV.</a>); others must be left in the dry form, -as before mentioned; and some few it is impossible to -preserve unchanged for any length of time. <em>Crystals</em>, -however, are amongst the most beautiful and interesting -subjects for polarisation; and it is very probable that, by -the aid of the polariscope, new and valuable facts are yet to -be made known. For one who finds pleasure in form and -colour, there is a field here which will only open wider upon -him as he advances; and instead of being in anywise a -merely mechanical occupation, it requires deep and careful -study. The little here said on the subject will show this in -some degree.</p> - -<p><span class="pagenum" id="Page_75">75</span> -With almost every salt the method of <em>crystallization</em> must -be modified to obtain the best forms; I may even go -further than this, and say that it is possible to change these -forms to such a degree that the eye can perceive no relationship -to exist betwixt them. If a solution of sulphate of -iron is made, a small quantity spread evenly upon a slide, -and then suffered to dry whilst in a flat position, the crystals -often resemble the fronds of the common fern in shape. But -if, whilst the liquid is evaporating, it is kept in motion by -stirring with a thin glass rod, the crystals form separately, -each rhombic prism having its angles well defined, and -giving beautiful colours with the polarized light. Again, -pyro-gallic acid, when allowed to flow evenly over the -slide in a saturated solution, covers the surface in long -“needles,” which are richly coloured by polarized light; but -if any small portion of dust or other matter should form a -nucleus around which these “needles” may gather, the -beauty is wonderfully increased. A form very closely resembling -the “eye” of the peacock’s tail, both in form and -colour, is then produced, which to one uninitiated in crystallography -bears very little resemblance to the original crystal. -From these simple facts it will be clearly seen that in this, -as in every other department, study and experience are -needful to give the best results.</p> - -<p>To obtain anything like uniformity in the formation of -crystals upon the glass slide, every trace of grease must -be removed by cleaning with liquor potassæ or ammonia -immediately before using, care also being taken that none -of the agent is left upon the slide, otherwise it may -interrupt and change their relative position, and even -their form.</p> - -<p>Amongst those which are generally esteemed, the most -beautiful are the crystals of oxalurate of ammonia. The -preparation of this salt from uric acid and ammonia is a -rather difficult process, and will not on that account be -described here; but when possessed, a small quantity of a -strong solution in water must be made, and a little placed<span class="pagenum" id="Page_76">76</span> -on the slide, and evaporated slowly. Part of the salt will -then be deposited in circles with the needle-like crystals -extending from common centres. They should then be -mounted in pure Canada balsam; and, when the best colours -are wanted, used with the selenite plate. Of this class of -crystal salicine is a universal favourite, and can be easily -procured of most chemists. The crystals may be produced -in two ways:—A small portion of the salt must be placed -upon the slide, and a strong heat applied underneath until -fusion ensues; the matter should then be evenly and thinly -spread over the surface. In a short time the crystals will -form, and are generally larger than those procured by the -following process; but the uncertainty is increased a little -when fusion is used, which, however, is desirable with many -salts. Secondly, make a saturated solution of salicine, -which in cold water is effected by adding one part of the -salt to eighteen parts of water. Lay a little upon the -slide, and allow it to evaporate spontaneously, or with -the aid of gentle heat. The crystals are generally uniform, -and with ordinary powers quite large enough to afford a -beautiful object. The circular shape and gorgeous colours -of this crystal have made it so great a favourite that there -are few cabinets without it.</p> - -<p>Many new forms may be procured by uniting two totally -different salts in solution in certain proportions. This is a -field affording new facts and beauties; but requires some -chemical knowledge and much perseverance to obtain very -valuable results. One of the most beautiful I have met with -has been composed of sulphate of copper and sulphate of magnesia. -The flower-like forms and uniformity of crystallization -when successful make it well worth a few failures at first; -and as I became acquainted with some new facts in my frequent -trials, I will give the preparation of the double salt -from the beginning.</p> - -<p>Make a saturated solution of the two sulphates, combined -in the proportion of three parts copper to one part magnesia, -and then add to the solution one-tenth of pure<span class="pagenum" id="Page_77">77</span> -water. Dust or other impurities should be guarded against, -and the slide made free from all trace of grease by cleaning -immediately before use with liquor potassæ or ammonia. A -drop of the solution should then be placed upon the slide, -and by a thin glass rod spread evenly upon the surface. -Heat this whilst in a horizontal position until the salt -remains as a viscous transparent substance, which will not -be effected until it is raised to a high degree. The slide may -now be allowed to cool, and when this is accomplished, the -flower-like crystals will be perceived forming here and there -upon the plate. When these are at any stage in which it is -wished to preserve them, a few seconds’ exposure to the fire, -as warm as the hand can comfortably bear, will stop the -expansion, when the portion which we wish to mount should -be cut off from the mass of salt by simply scratching the -film around, and pure Canada balsam with the thin glass -used. Breathing upon the film, or allowing the slide to become -cold and attract the moisture from the atmosphere, will -cause the crystallization to extend, and sometimes greatly -rob the effect; so it is necessary to mount quickly when the -desired forms are obtained. As the crystals are very uncertain -as to the place of their formation, I may here -mention that they may be got in <em>any</em> part of the slide by -piercing the film with a needle-point; but in some degree -this necessarily interferes with the centre. As the cause of -this has no need to be entered into here, and has been elsewhere -discussed, I shall only give the above directions, and -say that there is a great field in this branch of study which -the microscope alone has opened.</p> - -<p>It would be useless to enter into particulars respecting the -various salts and treatment they require, as a great difference -is effected even by the strength of the solution. There -are some crystals, also, which are called forth in insulated -portions, showing no formation upon the ground; but even -when mounted in any preserving fluid, and unchanged for a -year, a new action seems to arise, and a groundwork is produced -which bears little resemblance to the original crystal.<span class="pagenum" id="Page_78">78</span> -Sometimes this new formation adds to the beauty of the -slide; in other cases the reverse is the result, the slide being -rendered almost worthless. This action, I believe, frequently -arises from some liquid being contained in the balsam or -other mounting medium used; and this is rendered the more -probable by the crystallization being called forth in an hour -after the balsam diluted with chloroform is employed, -whereas no change would have taken place for months (if at -all) had pure balsam been used.</p> - -<p>Sections of some of the salts are very interesting -objects, but the method of procuring these and their nature -will be described in <a href="#CHAPTER_V">Chapter V.</a></p> - -<p>The scales of various fish have been before mentioned as -mounted “dry;” when, however, they are required for -polarising objects they are generally mounted in balsam, -and some few in liquid. The former method will be considered -here.</p> - -<p>The eel affords a beautiful object for this purpose. The -scales are covered by a thin “<em>skin</em>,” which may be slightly -raised with a knife and then torn off, in the same manner -as the covering of the geranium and other petals, described -in <a href="#CHAPTER_II">Chapter II.</a> The required portion may then be removed; -or if a piece of skin can be procured as stripped off in -cooking, the scales may be easily taken from the inner -surface. They must then be washed and thoroughly -cleaned. After drying, soak for a day in turpentine, and -mount in the ordinary manner with balsam. This is a -good polarising object; but the interest, and I think the -beauty, is increased by procuring a piece of eel’s skin with -the scales <i xml:lang="la" lang="la">in sitû</i>, washing and drying under pressure, and -mounting in balsam as before. The arrangement of the -scales produces beautiful “waves” of colour, which are -quite soothing to the eye after examining some of the very -gorgeous salts, &c.</p> - -<p>There are many scales of fish which are good subjects for -the polariscope when mounted in balsam; but as they require -no particular treatment, they need no mention by name.</p> - -<p><span class="pagenum" id="Page_79">79</span> -Among hairs we find some which are beautiful when -mounted in balsam and examined by polarized light. Some, -when wanted as common objects, are always used dry, as -before mentioned; but if they are intended to be shown as -<em>polarizing</em> objects, they must be placed in some medium. -The “Micrographic Dictionary” mentions a mode of making -an interesting object by plaiting two series of white horse-hairs -at an angle, mounting in balsam, and using with the -polariscope. All hairs, however, must be steeped in turpentine -for a short time before mounting, as they will thus -be rendered cleaner and more transparent. When this is -done, there is no difficulty in mounting them.</p> - -<p>Many of the “tongues” of fresh-water and marine -mollusca are deeply interesting and most beautiful objects -when examined by polarized light. As these are usually -mounted in balsam, I mention them in this place; but as -they must be removed from the animals by dissection, -particulars respecting them will not be entered into until -we come to the part in which that operation is described -(<a href="#CHAPTER_V">Chapter V.</a>).</p> - -<p>The manner of preparing and mounting many of the -Polyzoa and Zoophytes has been before described; but any -notice of <em>polarizing</em> objects would be incomplete without -some allusion to them. A small piece of the <i xml:lang="la" lang="la">Flustra -avicularis</i>, well prepared, is beautiful when examined in -this manner. No selenite is needed, and yet the colours -are truly gorgeous. It is often met with upon shells and -zoophytes of a large size, and will well repay the trouble -of searching for. Many of the Sertularidæ are very beautiful -with polarized light, and, indeed, no ramble upon the -seaside need be fruitless in this direction.</p> - -<p>The different <em>starches</em> are quite a study in themselves, -and are peculiarly connected with polarized light. They -are found in the cellular tissue of almost every plant in -small white grains which vary considerably in size; that -from the potato averages one-three-hundredth of an inch in -diameter, and that from arrow-root about one-six-hundredth.<span class="pagenum" id="Page_80">80</span> -To procure starch from any plant, the texture must first be -broken up or ground coarsely; the mass of matter must be -then well washed in gently-flowing water, and, as all starch -is totally insoluble in cold water, the grains are carried off -by the current and deposited where this is stayed. In procuring -it from the potato, as well as many other vegetables, -it is but necessary to reduce the substance to a coarse pulp -by the aid of a culinary “grater;” the pulp should then -be well agitated in water, and allowed to rest a short time, -when the starch will be found at the bottom, its lighter -colour rendering it easily distinguishable from the pulp. It -should, however, be washed through two or three waters to -render it perfectly clean.</p> - -<p>These grains have no crystalline structure, but present a -very peculiar appearance when examined with polarized -light. Each grain shows a dark cross whose lines meet at -the point where it was attached to the plant, called the -<i xml:lang="la" lang="la">hilum</i>. Round the grain, also, a series of lines are seen, as -though it were put together in plates. This is more distinctly -visible in some kinds than others.</p> - -<p>As to the mounting of these starches there is little to be -said. If the grains are laid upon the slide, and as small a -portion as possible of the balsam diluted with turpentine, -as before mentioned, be applied, they will cling to the glass -and allow the pure balsam to flow readily over them without -being so liable to imprison air-bubbles when the thin -glass is put upon them.</p> - -<p>The raphides, which were fully described in <a href="#CHAPTER_II">Chapter II.</a>, -when required for use with polarized light, must be mounted -in balsam, and many are found which give beautiful colours. -They require no peculiar treatment, but must be washed -quite clean before putting up.</p> - -<p>There is one class of objects for the polariscope which -differs in preparation from any we have yet considered, and -affords very beautiful specimens. Some of the plants, including -many of the grasses and the Equisetaceæ (<i>i. e.</i> horsetails), -contain so large a quantity of silica, that when the<span class="pagenum" id="Page_81">81</span> -vegetable and other perishable parts are removed, a skeleton -of wonderful perfection remains. This skeleton must be -mounted in balsam, the method of performing which will -now be considered.</p> - -<p>Sometimes the cuticle of the equisetum is removed from -the plant, others dry the stem under pressure, whilst the -grasses, of course, require no preparation. The vegetable -should be immersed in strong nitric acid and boiled for a -short time; an effervescence will go on as the alkalies are -being removed, and when this has ceased more acid should -be added. At this point the modes of treatment differ; -some remove the object from the acid and wash, and having -dried, burn it upon thin glass until all appears <em>white</em>, when -it must be carefully mounted in balsam. I think, however, -it is better to leave it in strong acid until all the substance, -except the required portion, is removed; but this will take -a length of time, varying according to the mass, &c., of the -plant. Of course, when this latter method is used, the -skeleton must be washed from the acid, &c., before being -mounted in balsam.</p> - -<p>These <em>siliceous cuticles</em> are readily found. The <em>straws</em> of -most of the cereals, wheat, oat, &c.; the <em>husks</em>, also, of some -of these; many <em>canes</em>; the equisetum, as before described; -and some of the grasses. Many of these are everywhere -procurable, so that the student can never want material for -a splendid object for the polariscope.</p> - -<p>In <a href="#CHAPTER_II">Chapter II.</a> the <em>scales</em> (or hairs) which are often found -upon the leaves of plants were mentioned as beautiful objects -when mounted dry; but some of these when detached from -the leaf—which is easily done by gently scraping it, when -dried, with a knife—present brilliant starlike and other -forms, if mounted in balsam and used with the polariscope. -There is a little danger, when placing the thin glass upon -the balsam, of forcing out the scales in the wave of matter -which is always ejected; this may be overcome by applying -to the slide, previously to placing the objects upon it, an -extremely thin covering of the balsam diluted with turpentine<span class="pagenum" id="Page_82">82</span> -as before mentioned, and thus giving them every chance -of adherence; or by using the balsam with chloroform, as -before noticed. These scales are much more abundant than -was formerly supposed, and daily new specimens are discovered; -so that the student should always be on the lookout -for them in his researches in the vegetable world.</p> - -<p>Most classes of objects, and the treatment they require -when mounting them in balsam, have now been considered. -The next chapter will be devoted to the preservative liquids, -and the best methods of using them.</p> - -<hr /> - -<p><span class="pagenum" id="Page_83">83</span></p> - -<div class="chapter"> -<h2 id="CHAPTER_IV" class="vspace"><span class="gesperrt">CHAPTER IV</span>.<br /> - -<span class="subhead">PRESERVATIVE LIQUIDS, ETC., PARTICULARLY WHERE CELLS ARE -USED.</span></h2> -</div> - -<p class="in0"><span class="firstword">There</span> are many objects which would lose all their distinctive -peculiarities if allowed to become dry, especially those -belonging to the fresh-water Algæ, many animal tissues, -and most of the very delicate animal and vegetable substances -in which structure is to be shown. These must be -preserved by immersion in some fluid; but it is evident that -the fluid must be suited to the kind of matter which it is -intended to preserve. As it often requires much study -and trouble to <em>obtain</em> microscopic objects of this class, it -is well that their <em>preservation</em> should be rendered as perfect -as possible; and for this reason the <span class="smcap smaller">CELLS</span>, or receptacles -of the fluids, should be so closed that all possibility of -escape should be prevented. The accomplishment of this -is not so easy a matter as it might appear to the inexperienced.</p> - -<p>Before giving any directions as to the manipulation -required in mounting the objects, we must consider the -different <em>liquids</em> and <em>cells</em> which are requisite for their -preservation. Of the former there are a great number, of -which the principal may be mentioned.</p> - -<p><span class="smcap">Distilled Water</span> is strongly recommended by many for -Diatomaceæ and other Protophytes. It has been, however, -stated that confervoid growths often disturb the clearness -of the liquid, and on this account various additions are -made to it. A lump of camphor is often left in the bottle, -so that the water may dissolve as much as possible. One -grain of bay-salt and one of alum are added to each ounce -of water; or a drop or two of creosote shaken up with the<span class="pagenum" id="Page_84">84</span> -ounce of water, which should be afterwards filtered. These -additions are often made; perhaps each of them good for -certain objects.</p> - -<p><span class="smcap">Glycerine.</span>—Some affirm this to be one of the best -preservative liquids, especially for vegetable objects; but -others think that it is much better when diluted with two -parts of camphor-water, prepared as above.<a id="FNanchor_E" href="#Footnote_E" class="fnanchor">E</a></p> - -<div class="footnote"> - -<p><a id="Footnote_E" href="#FNanchor_E" class="fnanchor">E</a> Dr. Carpenter says:—“Glycerine has a solvent power for carbonate -of lime, and should not be employed when the object contains -any calcareous structure. In ignorance of this fact, the author (Dr. -C.) employed glycerine to preserve a number of remarkably fine specimens -of the pentacrinoid larva of the Comatula, whose colours he was -anxious to retain; and was extremely vexed to find, when about to -mount them, that their calcareous skeletons had so entirely disappeared, -that the specimens were completely ruined.”</p></div> - -<p><span class="smcap">Glycerine and Gum.</span>—This is also believed to be a very -good liquid for vegetable tissues, and is thus <span class="locked">prepared:—</span></p> - -<table class="narrow15" summary="glycerine and gum"> - <tr> - <td class="tdl">Pure gum-arabic</td> - <td class="tdl">1 oz.</td></tr> - <tr> - <td class="tdl">Glycerine</td> - <td class="tdl">1 ”</td></tr> - <tr> - <td class="tdl">Water (distilled)</td> - <td class="tdl">1 ”</td></tr> - <tr> - <td class="tdl">Arsenious acid</td> - <td class="tdl">1½ grains.</td></tr> -</table> - -<p class="in0">Dissolve the arsenious acid in the cold water, then the gum, -add the glycerine, and mix without bubbles.</p> - -<p class="p2"><span class="smcap">Deane’s Compound.</span>—This is usually deemed about the -best medium for preserving Algæ, mosses, &c., and is thus -prepared:—Soak 1 oz. of best gelatine in 4 oz. of water -until the gelatine becomes soft, when 5 oz. of honey heated -to boiling-point are added; boil the mixture, and when -it has cooled, but not enough to become stiff, add ½ oz. -rectified spirit with which 5 or 6 drops of creosote have been -well mixed, and filter the whole through fine flannel. This -compound when cold forms a stiff jelly, the use of which -will be described elsewhere.</p> - -<p><span class="smcap">Glycerine Jelly.</span>—This mixture closely resembles the -above, but as the composition differs a little it may be -mentioned here. It is strongly recommended by Mr. -Lawrance in the <cite>Microscopic Journal</cite>, where he states “that<span class="pagenum" id="Page_85">85</span> -the beautiful green of some mosses mounted two years -ago, is still as fresh as the day they were gathered;” and -that this is the only medium he knows which will preserve -the natural colour of vegetable substances. He takes a -quantity of Nelson’s gelatine, soaks it for two or three -hours in cold water, pours off the superfluous water, and -heats the soaked gelatine until melted. To each fluid -ounce of the gelatine, <em>whilst it is fluid but cool</em>, he adds a -fluid drachm of the white of an egg. He then boils this -until the albumen coagulates and the gelatine is quite -clear, when it is to be filtered through fine flannel, and -to each ounce of the clarified solution add 6 drachms of a -mixture composed one part of glycerine to two parts of -camphor-water.</p> - -<p><span class="smcap">Goadby’s Fluid.</span>—This is much used in the preservation -of animal objects; and seldom, if ever, acts upon the colours. -It is thus prepared—Bay salt, 4 oz.; alum, 2 oz.; corrosive-sublimate, -4 grains. Dissolve these in two quarts of boiling -water and filter. For delicate preparations some recommend -that this mixture be reduced by the addition of an -equal quantity of water; but where there is bone or shell in -the object the above acts injuriously upon it, in which case -this fluid may be used:—Bay-salt 8 oz., corrosive sublimate -2 grains, water 1 quart.</p> - -<p><span class="smcap">Thwaites’ Liquid.</span>—This is recommended for the preservation -of Algæ, &c., as having little or no action on the -colour, and is thus prepared:—Take one part of rectified -spirit, add drops of creosote enough to saturate it; to this add -sixteen parts of distilled water and a little prepared chalk, -and filter. When filtered, mix with an equal quantity of -camphor-water (as before mentioned), and strain through -fine muslin before using.</p> - -<p><span class="smcap">Chloride of Zinc Solution.</span>—In the “Micrographic Dictionary” -this is stated to be “perhaps the best preservative -known for animal tissues.” Persons of great experience, -however, have given a very different opinion; but it is certainly -very useful in many cases where a small degree of coagulating<span class="pagenum" id="Page_86">86</span> -action is not injurious. It is used of strengths varying -according to the softness of the parts to be preserved; the -average being 20 grains of the fused chloride to 1 oz. of -distilled water. To keep this liquid a lump of camphor -may be left floating in the bottle. I have heard complaints -that this mixture becomes turbid with keeping, but I think -this must only be the case when some impurity has got into -the bottle.</p> - -<p><span class="smcap">Carbolic Acid.</span>—This substance has not been known -long enough to warrant any decided opinion upon its merits. -A solution of 1 part of acid to 20 of water has been -recommended on account of its antiseptic properties.</p> - -<p><span class="smcap">Castor Oil.</span>—This is a very useful preservative for -crystals and other objects. Many salts are quite destroyed -when Canada balsam is used with them; but very few are -acted upon by this oil. To use it, it must be dropped in -a sufficient quantity to cover the crystal or object to be -preserved with a thin coating of oil. It may be necessary -sometimes to spread it with a needle or other instrument. The -thin glass should then be carefully placed upon it, so that all -air may be excluded; and should any oil be forced out, owing -to the quantity used being too great, it must be removed -with blotting paper. When the edge of the thin glass cover -and the surrounding parts of the slide are as clean as -possible, a coating of sealing-wax varnish or liquid glue must -be applied and allowed to dry. A second or even a third coating -may be required, but not before the previous cover is quite -dry. These varnishes, however, are very brittle, and it is much -safer, as a finish, to use one of the tougher cements—gold-size, -for instance—which will render it doubly secure.</p> - -<p>The above are the principal liquids, &c., used for preserving -objects in cells. The different cells may be here -mentioned; and it is recommended that these should always -be kept some time before use in order that the cement may -become perfectly dry; and care must be taken that no -cement be used on which the preservative liquid employed -has any action whatever.</p> - -<p><span class="pagenum" id="Page_87">87</span> -<span class="smcap">Cement Cells.</span>—Where the object is not very thick, this -kind of cell is generally used. They are easily made with the -turntable before described; but when the objects to be -preserved are <em>very</em> minute, these cells need not be much -deeper than the <em>ordinary</em> circle of cement on the slide. -When, however, a comparatively great depth is required, it -is sometimes necessary to make the wall of the cell as deep -as possible, then allow it to dry and make another addition. -Of these cements gold-size is one of the most trustworthy, -and may be readily used for the shallow cells. The asphaltum -and india-rubber, before noticed, I have found very -durable when well baked, and exceedingly pleasant to work -with. It may be used of such a thickness as to give space -for tolerably large objects. Black japan also is much used. -Many cements, however, which are recommended by some -writers, are worse than useless, owing to the brittleness which -renders their durability uncertain, as sealing-wax varnish, -liquid-glue, &c.</p> - -<p>The student may feel himself at a loss in choosing the -cement which will give him the <em>safest</em> cells, many of them -becoming partially or wholly dry in a year or two, as stated -in another place. I can only give him a few general directions, -and he must then use his own judgment. Of course -it would be lost labour to employ any cement upon which -the preservative liquid has <em>any action whatever</em>. It is also -a good rule to avoid those in whose composition there are -any particles which do not become a thorough and intimate -portion, as these unreduced fragments will almost certainly, -sooner or later, prepare a road by which the liquid will -escape; and, lastly, whatever cement he uses, the cells are -always better when they have been kept a short time -before use, as already stated.</p> - -<p><span class="smcap">Gutta-percha Rings</span> have been recommended by some, as -affording every facility for the manufacture of cells for -liquids; but they cannot be recommended, as, after a certain -length of time, they become so brittle as to afford no safeguard -against ordinary accidents.</p> - -<p><span class="pagenum" id="Page_88">88</span> -Often the cells must necessarily be of a large size, and for -this reason are made by taking four strips of glass of the -thickness and depth required, and grinding the places where -these are to meet with emery, so as to form a slightly -roughened but flat edge. The glass strip must also be -ground on the side where it meets the plate, and each piece -cemented with the marine glue mentioned in <a href="#CHAPTER_I">Chapter I.</a> in -the following manner:—On that part of the glass to which -another piece is to be attached should be laid thin strips of -the glue; both pieces must then be heated upon a small -brass table, with the aid of the spirit-lamp, until the strips -become melted; the small piece is then to be taken up and -placed upon the spot to which it is to be attached, and so -on until the cell is completed. It will be found necessary to -spread the glue over the surface required with a needle or -some other instrument, so that an unbroken line may be -presented to the wall of the cell, and no bubbles formed. -Too great a heat will “burn” the marine-glue, and render -it brittle; care must be therefore taken to avoid this.</p> - -<p>When shallow cells are required, those which are made -by grinding a concavity in the middle of an ordinary slide -will be found very convenient. The concavities are cut both -circular and oblong; and the surface being flat, the cover is -easily fastened upon it. These are now cheap, and are very -safe as to leakage.</p> - -<p>Circular cells with a flat bottom used to be made by -drilling a hole through glass of the required thickness, and -fixing this upon an ordinary slide with marine-glue; but -the danger of breakage and the labour were so great that -this method is seldom used now, and, indeed, the rings about -to be mentioned do away with all necessity of it.</p> - -<p><span class="smcap">Glass Rings.</span>—Where any depth is required, no method -of making a cell for liquids is so convenient as the use of -glass rings, which are now easily and cheaply procurable. -They are made of almost every size and depth, and, except -in very extraordinary cases, the necessity for building cells -is completely done away with. These rings have both edges<span class="pagenum" id="Page_89">89</span> -left roughened, and consequently adhere very well to the -slide, this adherence being generally accomplished by the -aid of marine glue, as before noticed with the glass cells. -Gold-size has been occasionally used for this purpose; and -the adherence, even with liquid in the cell, I have always -found to be perfect. This method has the advantage of -requiring no heat, but the gold-size must be perfectly dry, -and the ring must have been fixed upon the slide some time -before use. Canada balsam has also been used for the same -purpose, but cannot be recommended, as when it is perfectly -dry it becomes so brittle as to bear no shock to which the -slide may be ordinarily exposed.</p> - -<p>These are the cells which are mostly used in this branch -of microscopic mounting. The mode of using them, and the -different treatment which certain objects require when intended -to be preserved in the before-mentioned liquids, may -now be inquired into.</p> - -<p>I may mention, however, that this class of objects is -looked upon by many with great mistrust, owing to the -danger there is of bubbles arising in the cells after the -mounting has been completed, even for years. I know -some excellent microscopists who exclude all objects in cells -and preservative liquids from their cabinets, because they -say that eventually almost all become dry and worthless; -and this is no matter of surprise, for many of them do -really become so. Perhaps this is owing to the slides being -sold before they could possibly be thoroughly dry. As to -the air-bubbles, I shall have something to say presently.</p> - -<p>We will now suppose the cell employed is made by -placing a glass ring upon the slide with marine glue or -gold-size, and is quite dry. Around the edge of the cleaned -thin glass which is to cover it, I trace with a camel-hair -pencil a ring of gold-size, and also around the edge of the -cell to which it is to adhere. Dr. Carpenter objects to this, -as rendering the later applications of the gold-size liable to -“run in.” All danger of this, however, is completely done -away with by leaving the slide and cover for awhile until<span class="pagenum" id="Page_90">90</span> -the cement becomes partially “fixed,” but still adhesive -enough to perform its function (<a href="#CHAPTER_II">Chapter II.</a>). With many -slides this is not accomplished in less than twenty-four -hours, even if left two or three days no injury whatever -ensues; but with other kinds an hour is too long to leave -the exposed cement, so that the operator must use his own -discretion. The liquid required may be drawn up by the -mouth into the pointed tube mentioned in <a href="#CHAPTER_I">Chapter I.</a>, and -then transferred to the cell. In the various books of instruction, -the object is now to be placed in the cell; this, -however, I think a great mistake, as another process is -absolutely necessary before we advance so far. The cell, -full of liquid, must be placed under the receiver of an air-pump, -and the air withdrawn. Almost immediately it will -be perceived that the bottom and sides of the cell are -covered with minute bubbles, which are formed by the air -that is held in suspension by the liquid. The slide may -now be removed, and the bubbles may require the aid of a -needle or other point to displace them, so obstinately do -they adhere to the surface of the glass. This process may be -then repeated, and one cause, at least, of the appearance of -bubbles in cells of liquid will be got rid of. The object to -be mounted should also be soaked in one or two changes of -the preservative liquid employed, and, during the soaking, -be placed under the air-pump and exhausted. It may -then be transferred to the cell, which will probably -cause the liquid to overflow a little. The cover with the -gold size applied to the edge must then be carefully laid -upon the cell, and slightly pressed down, so that all air-bubbles -may be displaced. The two portions of gold-size -will now be found to adhere wherever the liquid does not -remain, although the whole ring may have been previously -wet. The outer edge of the thin glass and cell must now -be perfectly dried, and a coating of gold-size applied. When -this is dry, the process must be repeated until the cement -has body enough to protect the cell from all danger of -leakage. When some preservative liquids are used, a<span class="pagenum" id="Page_91">91</span> -scum is frequently found upon the surface when placed in -the cell, which must be removed immediately before the cover -is laid upon it.</p> - -<p>I believe this method to be perfectly secure against -leakage when carefully performed; and some of my friends -have told me that their experience (some years) has been -equally satisfactory.</p> - -<p>In using some of the particular kinds of preservative -liquids, it will be found necessary to make slight change -in the manipulation. This will be best explained by -mentioning a few objects, and the treatment they require.</p> - -<p>For the preservation of the Mosses, Algæ, &c., Deane’s -compound is much used, and considered one of the best -media. The specimen to be mounted should be immersed -in the compound, which must be kept fluid by the vessel -containing it being placed in hot water. In this state the -whole should be submitted to the action of the air-pump, as -it is not an easy matter to get rid of the bubbles which form -in and around the objects. The cell and slide must be -warmed; and heat will also be necessary to render the -gelatine, &c., fluid enough to flow from the stock-bottle. -The cell may then be filled with the compound, and the -specimen immersed in it. A thin glass cover must then be -warmed, or gently breathed upon, and gradually lowered -upon the cell, taking care, as with all liquids, that no -bubbles are formed by the operation. The cover may be -fixed by the aid of gold-size, Japan, or any of the usual -varnishes, care being taken, as before, that all the compound -is removed from the parts to which the varnish is intended -to adhere.</p> - -<p>The glycerine jelly of Mr. Lawrance, before mentioned, -requires almost a similar treatment. “The objects to be -mounted in this medium should be immersed for some time -in a mixture of equal parts of glycerine and dilute alcohol -(six of water to one of alcohol). The bottle of glycerine jelly -must be placed in a cup of hot water until liquefied, when it -must be used like Canada balsam, except that it requires<span class="pagenum" id="Page_92">92</span> -less heat. A ring of asphaltum varnish round the thin glass -cover completes the mounting.”</p> - -<p>The Infusoria (see <a href="#CHAPTER_III">Chapter III.</a>) are sometimes preserved -in liquid; but present many difficulties to the student. -Different kinds require different treatment, and consequently -it is well, when practicable, to mount similar objects in two -or more liquids. Some are best preserved in a strong -solution of chloride of calcium, others in Thwaites’ liquid, -whilst a few keep their colour most perfectly when in -glycerine alone. Many of them, however, are so very transparent -that they present but faint objects for ordinary -observance. The Desmidiaceæ require somewhat similar -treatment, and may be mentioned here. The solution of -chloride of calcium has been strongly recommended; but no -preservative liquid seems to be without some action upon -them. Both of the above classes of objects should be mounted -in shallow cells, so as to allow as high a microscopic power -as possible to be used with them.</p> - -<p>Many of the <span class="smcap">Zoophytes</span> which are obtained on our sea-coasts -are well preserved by mounting in cells, in the manner -before mentioned, with Goadby’s fluid, or distilled water -with one of the additions noticed amongst the preservative -liquids. For examination by polarized light, however, they -are usually mounted in balsam (see <a href="#CHAPTER_III">Chapter III.</a>), whilst -those in cells present a more natural appearance as to -position, &c., for common study.</p> - -<p>As to the use of preservative liquids with the Diatomaceæ -there are various opinions. Some experienced microscopists -say that there is little or no satisfaction in mounting them -in this way. Dr. Carpenter, however, explains this difference -by his instructions as to what method should be used -when certain ends are desired. He says: “If they can be -obtained quite fresh, and it be desired that they should -exhibit as closely as possible the appearance presented by -the living plants, they should be put up in distilled water -within cement-cells; but if they are not thus mounted within -a short time after they have been gathered, about a sixth<span class="pagenum" id="Page_93">93</span> -part of alcohol should be added to the water. If it be -desired to exhibit the stipitate forms in their natural parasitism -upon other aquatic plants, the entire mass may be -mounted in Deane’s gelatine in a deeper cell; and such a -preparation is a very beautiful object for the black-ground -illumination. If, on the other hand, the minute structure of -the siliceous envelopes is the feature to be brought into -view, the fresh diatoms must be boiled in nitric or hydrochloric -acid” (which process is fully described in <a href="#CHAPTER_II">Chapter -II.</a>). It is very convenient to have many of these objects -mounted by two or more of the above methods; and if they -are to be studied, this is indispensable. Mr. Hepworth -once showed me about one hundred slides which he had -mounted in various ways, for no other purpose than the -study of the fly’s foot.</p> - -<p>My friend, Mr. Rylands, successfully mounts the diatoms -in the state in which he finds them, and gave me the following -method as that which he always employs. He says -that he has had no failures, and hitherto has found his -specimens unchanged. Take a shallow ring cell of asphalt -or black varnish (which must be at least three weeks old), -and on the cell, whilst revolving, add a ring of benzole and -gold-size mixed in equal proportions. In a minute or two -pure distilled water is put in the cell until the surface is -slightly convex. The object having been already floated on -to the cover (the vessel used for this purpose being an ordinary -indian-ink palette), is now inverted and laid carefully -upon the water in the cell. By these means the object may -be laid down without being removed. The superfluous -moisture must not be ejected by pressure, but a wetted -camel-hair pencil, the size made in an ordinary quill, being -partially dried by drawing through the lips, must be used -repeatedly to absorb it, which the pencil will draw by -capillary attraction as it is very slowly turned round. When -the cover comes in contact with the benzole and gold-size ring, -there is no longer any fear of the object being removed, and -a slight pressure with the end of the cedar stick of the<span class="pagenum" id="Page_94">94</span> -pencil will render the adhesion complete, and cement the -cover closely and firmly to the cell. When dry, an outer -ring of asphalt makes the mounting neat and complete.</p> - -<p>The <i xml:lang="la" lang="la">Fungi</i> have been before mentioned; but it may be -here stated that some few of the minute forms are best preserved -in a very shallow cell of liquid. For this purpose -creosote-water may be advantageously used.</p> - -<p>The <i xml:lang="la" lang="la">antennæ</i> of insects have been before noticed as being -very beautiful when mounted in balsam. This is readily -accomplished when they are large; but those of the most -minute insects are much more difficult to deal with, and are -less liable to injury when put up in fluid. <em>Goadby’s Fluid</em> -serves this purpose very well; but, of course, the object -must be thoroughly steeped in the liquid before it is -mounted, for a longer or shorter time according to the -thickness.</p> - -<p>The <em>eggs of insects</em> afford some worthy objects for the -microscope, amongst which may be mentioned those of the -common cabbage butterflies (small and great), the meadow-brown, -the puss-moth, the tortoiseshell butterfly, the bug, -the cow-dung fly, &c. These, however, shrivel up on becoming -dry, and must, therefore, be preserved in some of -the fluids before mentioned. To accomplish this no particular -directions are required; but the soaking in the liquid -about to be employed, &c., must be attended to as with other -objects.</p> - -<p><em>Glycerine</em> may be advantageously used for the preservation -of various insects. These should first be cleaned with -alcohol to get rid of all extraneous matter, and then, after -soaking in glycerine, be mounted with it like other objects. -This liquid may also be used for the Entomostraca, which -offer a wide field for study. They are to be found abundantly -in ponds of stagnant water, &c. Some insects, such -as May-flies, &c., are, however, often preserved by immersion -in a solution of one part of chloride of calcium in -three or four parts of water; but this has not been recommended -amongst the “preservative liquids,” as the colour,<span class="pagenum" id="Page_95">95</span> -which is often an attractive quality of this class of objects, -is thereby destroyed.</p> - -<p>We have now noticed the treatment which must be applied -to those objects which are to be preserved in liquids -and cells. We may here state that all slides of this kind -should be examined at short intervals, as they will be found -now and then to require another coating of varnish round -the edge of the thin glass cover to prevent all danger of -leakage. The use of the air-pump, in the first instance -(as before recommended), and this precaution as to the -varnish, will render the slides less liable to leakage and air-bubbles, -which so very frequently render them almost -worthless.</p> - -<hr /> - -<p><span class="pagenum" id="Page_96">96</span></p> - -<div class="chapter"> -<h2 id="CHAPTER_V" class="vspace"><span class="gesperrt">CHAPTER V</span>.<br /> - -<span class="subhead">SECTIONS AND HOW TO CUT THEM, WITH SOME REMARKS ON -DISSECTION.</span></h2> -</div> - -<p class="in0"><span class="firstword">Many</span> objects are almost worthless to the microscopist until -the extraneous matter is removed from them; and this is -frequently difficult in the extreme to perform satisfactorily. -As an instance, certain Foraminifera may be mentioned in -which the cells are placed one upon another, consequently -the object must be reduced to a certain degree of <em>thinness</em> -before a single uniform layer of these cells can be obtained -to show something of the internal arrangements.</p> - -<p>Most animal and vegetable forms require an examination -of the separate parts before much can be known about -them. The mass must be divided into separate portions, -each part intended to be preserved being cleaned from the -useless matter with which it is surrounded. It will frequently -be found necessary to make thin sections, which -from a very tender substance is no easy matter; and much -patience will be necessary to attain anything like proficiency.</p> - -<p>This making of sections was not until very recently -entered into by many except those belonging to the medical -profession, but I do not see why this should be so, as much -may be accomplished by a persevering and interested mind -where there is time for entering into the subject. I will -therefore make an attempt to give some instructions on this -subject also. We will first consider the cutting of sections -from hard substances, in which the ordinary knife, chisel, -&c., are of no avail. Most of these require no particular -care in mounting, but are placed in balsam like the other -objects noticed in <a href="#CHAPTER_III">Chapter III.</a>: where, however, any special<span class="pagenum" id="Page_97">97</span> -treatment is necessary it will be commented upon as we -proceed.</p> - -<p><span class="smcap">Shells, &c.</span>—It is seldom, if ever, necessary to possess -apparatus for this process except a small thin saw made -with a steel blade, for which a piece of watch-spring serves -very well; a fine stone such as is used for sharpening pen-knives; -and two smooth leather strops, one of which is to -be used with putty-powder to polish the section after -grinding, and the other dry, to give the final surface. It is, -however, very convenient to have three or four files of -different degrees of fineness. The shell, if very thick, may -be divided by using the watch-spring saw; and this section -may then with ordinary care be rubbed down with water on -the stone until one side of it is perfectly flat. When this is -accomplished it must be again rubbed with putty-powder -upon the strop, and finally upon the other strop without the -powder. This surface will then be finished and must be -firmly united to the slide in the position it is intended to -occupy. To do this a small quantity of Canada balsam may -be dropped upon the middle of the slide and heated over the -lamp until on cooling it becomes hard; but this must be -stopped before it is rendered brittle. Upon this the polished -surface must be laid, and sufficient heat applied to allow the -object to fall closely upon the slide, when slight pressure may -be used to force aside all bubbles, &c. On cooling, the adherence -will be complete enough to allow the same grinding -and polishing upon the upper surface which the lower received. -Whilst undergoing this, the section must be examined from -time to time to ascertain whether the necessary degree of thinness -has been reached. When this is the case the section -should be washed thoroughly and dried. It must then be -covered, which is best done by using the ordinary Canada -balsam, as recommended in <a href="#CHAPTER_III">Chapter III.</a></p> - -<p>Sections of some exquisitely beautiful objects are cut with -much less trouble than the above. The Orbitolite, for -instance, may be prepared in this manner. Take the -object and by pressure with the finger rub the side upon<span class="pagenum" id="Page_98">98</span> -a flat and smooth sharpening stone with water until the -portion is reached which it is wished to show. The -strength of the object will easily allow this to be accomplished -with ordinary care. This side may then be -attached to the glass slide with heated balsam, as above -described, and the object may then be gently rubbed down -to the degree of thinness required to show it to the best -advantage. After removing all disengaged matter from the -object by washing and thoroughly drying, it may be -mounted in balsam in the usual manner, when it is equally -beautiful as a transparent or opaque object. From this it -will be seen that in many instances where a smooth stone is -found sufficient for the work (which is often the case when -the section is mounted in balsam) the final process of polishing -advised above may be dispensed with, as in the Orbitolite, -Nummulite, &c., &c. It is quite necessary that the stones on -which the objects are rubbed be <em>perfectly flat</em>, otherwise one -side must be acted upon before the other, and it will be -found impossible to attain anything like uniformity. Where -it is not practicable to cut a section and the object is very -thick, a coarse stone may be first used to reduce it and the -smoother afterwards.</p> - -<p>The consideration of the cutting of sections from shells -would scarcely be deemed complete without some mention -of what Dr. Carpenter terms the decalcifying process. -Muriatic acid is diluted with twenty times its volume of -water, and in this the shell is immersed. After a period, -differing according to the thickness of the shell, the carbonate -of lime will be dissolved away, and a peculiar membrane -left, showing the structure of the shell very perfectly. -This may be mounted dry, in balsam, or sometimes in -liquid, according to the appearance of the object; but no -rule can be given. The discretion of the student, however, -will enable him to choose the most suitable method.</p> - -<p>From some shells it is easy to divide thin plates, or -“laminæ,” which require nothing but mounting in Canada -balsam to show the texture very well. In working, however,<span class="pagenum" id="Page_99">99</span> -with those which are “pearly,” it will be found that experience -and patience are needed, as they are very brittle and -peculiarly hard; but a little practice will overcome these -difficulties.</p> - -<p>Amongst the Echinodermata, which include the star-fishes, -sea-hedgehogs, &c., there are many whose outer -surface is covered with “spines,” or thin projections. Some -of these are sharp and thorn-like, others blunt, longer or -shorter, and, indeed, of endless variety. In many of these, -when a section is made, rings are seen which have a common -centre, with radiating supports, resembling sections of -some of the woods. These are very beautiful objects, and -methods of procuring them may now be considered. It is -the best to cut as thin a section as can safely be got with -the watch-spring saw first, when the smooth “sharpening -stone” may be used to polish one side, which is easily -accomplished with water only. When this is effected, it -must be washed clean, and <em>thoroughly</em> dried, and then may -be united to the slide in the same manner as before recommended -for the Orbitolite, &c. If it is ever necessary to -displace it on account of inequalities, bubbles, or other -remediable fault, this may be done by warming the slide; -though too much heat must be avoided, otherwise fresh -bubbles will certainly be produced. The covering with thin -glass, balsam, &c., will present no difficulty to the student; -but he must remember that the transparency is somewhat -increased by this last operation.</p> - -<p><em>Corals</em> are often treated in this way, in order to reveal -their structure. Except, however, the student has had -much practice, he will often find this a most difficult task, -as many of them are exceedingly brittle. He will find the -method before described equally applicable here, and should -take both horizontal and vertical sections.</p> - -<p><span class="smcap">Coal.</span>—This substance is one of the most interesting -objects to the microscopist. It is, of course, of a vegetable -origin; and though this is in many cases of such minute -separate portions as to have lost all appearance of vegetation,<span class="pagenum" id="Page_100">100</span> -yet it is very frequently met with in masses, bearing the -form, even to the minute markings, of wood, in various -directions. To see this and prepare it for microscopic -research, a suitable piece of coal must be obtained; but in -every case the cutting and preparation of these sections -require great care and skill. Sometimes the coal is first -made smooth on one side, fastened to the glass, reduced to -the requisite degree of thinness, and finished in the method -before described. This mode of treating it is sometimes, -however, very tantalizing, as, at the last moment, when the -section is about thin enough, it often breaks up, and so -renders the trouble bestowed upon it fruitless. The dark -colour and opacity of coal render an extraordinary thinness -necessary, and so increase the liability to this accident.</p> - -<p>Perhaps the best method which can be pursued is that -recommended in the “Micrographic Dictionary,” which is as -follows:—“The coal is macerated for about a week in a -solution of carbonate of potash; at the end of that time it -is possible to cut tolerably thin slices with a razor. These -slices are then placed in a watch-glass with strong nitric -acid, covered and gently heated; they soon turn brownish, -then yellow, when the process must be arrested by dropping -the whole into a saucer of cold water, else the coal would be -dissolved. The slices thus treated appear of a darkish -amber colour, very transparent, and exhibit the structure, -when existing, most clearly. We have obtained longitudinal -and transverse sections of coniferous wood from various -coals in this way. The specimens are best preserved in -<em>glycerine</em> in cells; we find that spirit renders them opaque, -and even Canada balsam has the same defect. Schulz -states that he has brought out the cellulose reaction with -iodine, in coal treated with nitric acid and chlorate of -potash.”</p> - -<p><em>Cannel-coal</em> is so close and firm in its structure as to -be much used instead of jet in the manufacture of ornaments: -it takes a beautiful polish, and consequently presents -the student with none but ordinary difficulties in getting<span class="pagenum" id="Page_101">101</span> -sections of it. Its formation is somewhat different from -that of coal, sometimes showing the transition very clearly.</p> - -<p>In <em>flint</em> there are often found remains of sponges, shells, -Diatomaceæ, &c.; but to show these well, sections must be -cut and polished by the lathe and wheel of the lapidary, which -the microscopic student seldom possesses. Thin chippings -may, however, be made, which when steeped in turpentine -and mounted in balsam, will frequently show these remains -very well.</p> - -<p><em>Teeth</em> are very interesting objects to all microscopists, -more especially to those who give much study to them; as -the class of animal may very frequently be known from one -solitary remaining tooth. To examine them thoroughly, it -is necessary to cut sections of them; but this is rather difficult -to perform well, and needs some experience. Some -instructions, however, will at least lessen these difficulties, -and we will now endeavour to give them.</p> - -<p>It is generally thought that Canada balsam injures the -finer markings of these sections, consequently, they are -almost invariably mounted <em>dry</em>. A thin piece is first cut -from the tooth with the saw of watch-spring before -mentioned, if possible; but should the substance be too hard -for this, the wheel and lathe must be used with diamond -dust. If this cannot be procured, there is no alternative -but to rub down the whole substance as thin as practicable -on some coarse stone or file. The surface will then be rough; -but this may be much reduced by rubbing upon a flat sharpening -stone with the finger, or a small piece of gutta-percha, -upon the object to keep it in contact. The scratches may -be much lessened by this, but not so thoroughly removed as -microscopic examination requires in dry sections. It must, -therefore, be polished with the putty-powder and dry strop, -as recommended in the working of the shell-sections. The -other side of the section of the tooth may then be rubbed -down to the requisite thinness, and polished in the same -manner, when the dust and other impurities must be removed -by washing, after which the section must be carefully dried<span class="pagenum" id="Page_102">102</span> -and mounted. Some of these sections are equally interesting -as opaque or transparent objects.</p> - -<p>The dentine of the teeth may be decalcified by submersion -of the section in dilute muriatic acid; after drying and -mounting in Canada balsam it presents a new and interesting -appearance, showing the enamel fibres very beautifully -when magnified about three hundred diameters. A friend -tells me that after submersion of the <em>whole tooth</em> in the acid -he has been able to cut sections with a razor.</p> - -<p><span class="smcap">Sections of Bone.</span>—With the aid of the microscope few -fragmentary remains have proved so useful to the geologist -and students of the fossil kingdom as these. From a single -specimen many of our naturalists can tell with certainty to -what <em>class</em> of animal it has once belonged. To arrive at -this point of knowledge much study is necessary, and sections -of various kinds should be cut in such a manner as will best -exhibit the peculiarities of formation. The methods of -accomplishing this will now be considered. It may, however, -be first mentioned that the chippings of some bones will be -found useful now and then, as before stated with flint, -though this is by no means a satisfactory way of proceeding. -Sometimes the bones may be procured naturally so thin that -they may be examined without any cutting; and only -require mounting <em>dry</em>, or in <em>fluid</em>, as may be found the -best.</p> - -<p>When commencing operations we must provide the same -apparatus as is needed in cutting sections of teeth, before -described. A fine saw, like those used for cutting brass, &c.; -two or three flat files of different degrees of coarseness; -two flat “sharpening” stones; and a leather strop with -putty-powder for polishing. As thin a section as possible -should first be cut from the part required by the aid of the -fine saw; and it is better when in this state to soak it for -some short time in camphine, ether, or some other spirit to -free it from all grease. With the aid of a file we may -now reduce it almost to the necessary degree of thinness, -and proceed as before recommended with teeth. The<span class="pagenum" id="Page_103">103</span> -“sharpening” stone will remove all scratches and marks -sufficiently to allow it to be examined with the microscope -to see if it is ground thin enough; and if it is to be mounted -<em>dry</em> we must polish it with putty-powder and water upon -the strop to as high a degree as possible, and having washed -all remains of polishing powder, &c., from the section we -must place it upon the slide and finish it as described in -<a href="#CHAPTER_II">Chapter II.</a></p> - -<p>If the bone is not sufficiently hard in its nature to bear -the above method of handling whilst grinding and polishing—as -some are far more brittle than others—as thin a section -as possible must first be cut with the saw, and one surface -ground and polished. The piece must then be dried and -united to the glass by heated balsam in the same manner -as shells, &c. After which the superabundance of balsam -must be removed from the glass; then rub down upon the -stone and strop as before. When the polishing is completed -the whole slide must be immersed in chloroform, ether, or -some other spirit, to release and cleanse the section, when -it may be mounted as the one above mentioned.</p> - -<p>Some have recommended a strong solution of isinglass -to affix the half-ground teeth or bones to the glass as -causing them to adhere very firmly and requiring no heat, -and also being readily detached when finished.</p> - -<p>The reason why the sections of bone are usually mounted -<em>dry</em> is that the “<i xml:lang="la" lang="la">lacunæ</i>,” bone cells, and <i xml:lang="la" lang="la">canaliculi</i> (resembling -minute canals) show their forms, &c., very perfectly -in this state, as they are hollow and contain air, whereas -if they become filled with liquid or balsam—which does -sometimes occur—they become almost indistinguishable. -There are some dark specimens, however, where the cells -are already filled with other matter, and it is well to mount -these with balsam and so gain a greater degree of transparency.</p> - -<p>To gain a true knowledge of the structure of bone, -sections must be cut as in wood, both transversely and -longitudinally; but with <i>fossil</i> bones, without the lapidary’s<span class="pagenum" id="Page_104">104</span> -wheel, &c., it is a laborious task, and indeed can seldom be -properly accomplished. In this place, also, it may be -mentioned that by submitting bone to the action of muriatic -acid diluted ten or fifteen times with water, the lime, &c., is -dissolved away and the cartilage is left, which may be cut -into sections: in <i>caustic potash</i> the animal matter is got -rid of. Both of these preparations may be mounted in -fluid.</p> - -<p>The method of cutting thin sections of bone may be also -employed with the stones of fruit, vegetable ivory and such -like substances; many of which show a most interesting -arrangement of cells, especially when the sections are transverse. -Most of these objects present a different appearance -when mounted <i>dry</i> to that which they bear when <i>in balsam</i>, -owing to the cells becoming filled; and to arrive at a true -knowledge of them we must have a specimen mounted in -both ways.</p> - -<p>To those who study polarized light, few objects are more -beautiful than the sections of the different kinds of horn. -We will briefly inquire into the best method of cutting these. -There are three kinds of horn, the first of which is hard, -as the stag’s, and must be cut in the same manner as bone. -The second is somewhat softer, as the cow’s. The third is -another and still softer formation, as the “horn” (as it is -termed) of the rhinoceros. In cutting sections of the two -last we should succeed best by using the machine invented -for these purposes which I shall shortly describe when the -method of cutting wood is considered. To aid us in this -when the horn is hard it must be boiled for a short time in -water, when the cutting will be more easily accomplished. -The sections should be both transverse and longitudinal, -those of the former often showing cells with beautiful crosses, -the colours with the selenite plate being truly splendid. Of -this class the rhinoceros horn is one of the best; but the -buffalo also affords a very handsome object. The cow’s, and -indeed almost every different kind of horn, well deserves the -trouble of mounting. Whalebone, when cut transversely,<span class="pagenum" id="Page_105">105</span> -strongly resembles those of the third and softer formation. All -these are best seen when mounted in Canada balsam, but -care must be taken that they have been thoroughly dried -after cutting, and then steeped in turpentine.</p> - -<p>An interesting object may also be procured from whalebone -by cutting long sections of the hairs of which it is -composed. Down the centre of each hair we shall find a -line of cells divided from one another very distinctly. And -(as recommended in the “Micrographic Dictionary”) if -whalebone be macerated twenty-four hours in a solution of -caustic potash it will be softened, and by afterwards digesting -in water, the outer part will be resolved into numerous -transparent cells, which will show more plainly the structure -of this curious substance.</p> - -<p>In a former chapter, hairs were mentioned, their many and -interesting forms, and their beauty when used with polarized -light. The sections of them, however, are no less a matter -of study, as this mode of treatment opens to sight the outer -“casing,” and the inner substance somewhat resembling the -pith of plants.</p> - -<p>It would be out of place to enter into the description -of the different forms met with; but the ways in which -sections are to be procured may be glanced at. If transverse -sections are required, some place a quantity of hairs -betwixt two flat pieces of cork, which by pressure hold them -firmly enough together to allow the required portions to be -cut with a razor. Others take a bundle of the hairs and dip -it into gum or glue, which gives it when dry a solidity equal -to wood. Sections of this are then cut with the machine -mentioned a little further on, and these may be mounted in -balsam. The human hair is easily procured in the desired -sections by shaving as closely as possible a second time and -cleansing from the lather, &c., by carefully washing. Most -hairs, however, should be examined both transversely and longitudinally. -It is not difficult to procure the latter, as we -may generally split them with the aid of a sharp razor. In -a great number of hairs there is a quantity of greasy matter<span class="pagenum" id="Page_106">106</span> -which must be got rid of by soaking in ether or some other -solvent before mounting.</p> - -<p>We may next consider the best method of procuring -<em>sections of wood</em>, which must be cut of such a degree of -thinness as to form transparent objects, and so display all -the secrets of their structure. There is no monotony in -this study, as the forms are so various, and the arrangement -of the cells and woody fibre so different, that the -microscopist may find endless amusement or study in -it. From a single section the <em>class</em> of trees to which it -has belonged may be known, often even when the wood is -<em>fossil</em>. The apparatus best adapted for cutting these -sections is made as follows:—A flat piece of hard wood, -about six inches long, four wide, and one thick, is chosen, -to which another of the same size is firmly fixed, so as to -form, in a side view, the letter <span class="sans">T</span>. On one end of the upper -surface is fastened a brass plate, perfectly flat, in the centre -of which a circular opening is cut about half an inch in -diameter. Coinciding with this opening is a brass tube, -fixed in the under side of the table (if it may be termed so). -This tube is so cut at the bottom as to take a fine screw. -Another screw is also placed at the same end of the “table,” -which works at right angles to this, so that any substance -in the tube may be wedged firmly by working this last -screw. To use this instrument, the piece of wood or other -object of which a section is required must be placed in the -tube, when, by turning the screw underneath, the wood is -raised above the brass plate more or less as wished, and by -using the screw at the end, it is held firmly in the same -position. With a flat chisel the portion of the object which -projects above the surface of the brass plate may now be -cut off, and by means of the bottom screw another portion -may be raised and treated in the same manner. As to the -thickness of which objects should be cut, no proper directions -can be given, as this differs so greatly that nothing but -experience can be any guide. The same thickness can be -obtained by working the screw underneath in uniform<span class="pagenum" id="Page_107">107</span> -degrees, the head being marked for this purpose; and when -the substance to be cut is <em>very</em> much smaller than the hole -in the brass plate, it may be wedged with cork.</p> - -<p>As this instrument is peculiarly adapted for cutting wood -(though used for other substances, as before mentioned), I -shall notice a few particulars concerning this branch of -sections. It may here be remarked, that to obtain anything -like a true knowledge of the nature of wood, it should be -cut and examined in at least two directions, <em>across</em> and -<em>along</em>. The piece of wood is often placed in spirits for a -day or two, so that all resinous matter may be dissolved -out of it; it must then be soaked in water for the same -length of time, so as to soften and render it easy to cut. -Sections are obtained in the manner described above, -but often curl to such a degree as to make it necessary to -immerse them in water, from which they may be taken and -dried under slight pressure. They are often mounted <em>dry</em>, -and require no care beyond other objects, as in <a href="#CHAPTER_II">Chapter -II.</a> Some, however, are best mounted in balsam, particularly -the long sections when used for the polariscope; -these must be soaked in turpentine, and the greatest -care taken that all air bubbles are got rid of. Others are -thought to be most useful when mounted in shallow cells -with some of the <em>preservative liquids</em> mentioned in <a href="#CHAPTER_IV">Chapter -IV.</a>—weak spirit and water, chloride of calcium solution -of the strength of one part of the salt to three parts of -distilled water, &c.</p> - -<p>The above “<em>section-cutter</em>” may not be within the reach -of every student, nor is it absolutely necessary; though -where any <em>great number</em> of specimens is required it is very -useful, and insures greater uniformity in the thickness. -Many employ a razor for the purpose, which must always -be kept sharp by frequent stropping. Sections of -leaves also may be procured by the same means, though, -as before mentioned, they are sometimes easily divided by -stripping the coatings off with the fingers. The cells -which come to sight by cutting some of the orchideous<span class="pagenum" id="Page_108">108</span> -plants are most interesting. To cut these leaves they may -be laid upon a flat piece of cork, thus exposing the razor -to no danger of injury by coming in contact with the -support. It may be mentioned here that the <em>razor</em> may -also be used in cutting sections of the rush, than which a -more beautiful object can scarcely be found when viewed -transversely, as it shows the stellate arrangements of the -ducts to convey the liquids to the different parts of the -plant very clearly. This should be mounted <em>dry</em>. In the -same way sections of the leaf-stalks of ferns may also be -cut, some of which, as Dr. Carpenter states, show the -curious ducts very beautifully, especially when cut rather -obliquely.</p> - -<p>When sections of the softer substances are required, no -instrument can be compared with “Valentin’s knife,” which -consists of two steel blades lying parallel with one another -and attached at the lower end. The distance of separation -may be regulated at will by a small screw near the handle. -When, therefore, a section is wanted, the substance must be -cut through, and betwixt the blades a thin strip will be -found, which may be made of any thickness, according to -the distance of their separation. By loosening the screw -the blades may be extended, and the section may be floated -out in water if the damp will not injure it. The knife cuts -much better if dipped in water immediately before use and -also when the substance to be operated upon is wet, or even -under water altogether; but care must be taken, after use, -to clean the blades thoroughly and oil them before laying -by, if the place is at all damp. This instrument is most -useful in such subjects as anatomical preparations where -the sections are required to show the position of the different -vessels, &c.; but, as before stated, is very valuable for all -soft substances. As an instance of this, it may be mentioned, -that it is frequently used in cutting sections of sponges; -but as these are often very full of spicula, &c., it is much -better to press the sponge flat until dry, and then cut off -thin shavings with a very sharp knife; these shavings will<span class="pagenum" id="Page_109">109</span> -expand when placed in water. After this they may be laid -betwixt two flat surfaces and dried, when they may be -mounted as other dry objects, or, when desirable, in balsam.</p> - -<p><em>Valentin’s knife</em> is very much used in taking sections of -skin, which are afterwards treated with potash solution, -acids, &c., to bring out in the best way the different portions. -Dr. Lister’s mode, however, of getting these is thus -given in the <cite>Microscopic Journal</cite>:—“But I afterwards -found that much better sections could be obtained from -dried specimens. A portion of shaved scalp being placed -between two thin slips of deal, a piece of string is tied -round them so as to exercise a slight degree of compression; -the preparation is now laid aside for twenty-four hours, -when it is found to be dried to an almost horny condition. -It then adheres firmly by its lower surface to one of the -slips, and thus it can be held securely, while extremely thin -and equable sections are cut with great facility in any plane -that may be desired. These sections, when moistened with -a drop of water and treated with acetic acid, are as well -suited for the investigation of the muscular tissue as if they -had not been dried.”</p> - -<p>There are many who almost confine their attention to -polarized light and its beautiful effects. Such would not -deem these efforts to aid the student in cutting sections -complete without some notice of those which are taken -from various crystals, in order to display that curious and -beautiful phenomenon, <em>the rings with a cross</em>. The arrangement -of these is somewhat changed by the crystal which -affords the section; but nitrate of potash gives two sets of -rings with a cross, the long line of which passes through -both, the short line dividing it in the middle.</p> - -<p>The process of cutting these sections is rather difficult, -but a little care and perseverance will conquer all this. -The following is extracted from the <cite>Encyclopædia Metropolitana</cite>:—“Nitre -crystallizes in long six-sided prisms -whose section, perpendicular to their sides, is the regular -hexagon. They are generally very much interrupted in<span class="pagenum" id="Page_110">110</span> -their structure; but by turning over a considerable quantity -of the ordinary saltpetre<a id="FNanchor_F" href="#Footnote_F" class="fnanchor">F</a> of the shops specimens are readily -found which have perfectly transparent portions of some -extent. Selecting one of these, cut it with a knife into a -plate <em>above</em> a quarter of an inch thick, directly across the -axis of the prism, and then grind it down on a broad wet -file till it is reduced to about one quarter or a sixth of an -inch thick, smooth the surface on a wet piece of emeried -glass, and polish on a piece of silk strained very tight over -a strip of plate-glass, and rubbed with a mixture of tallow -and colcothar of vitriol. This operation requires practice. -It cannot be effected unless the nitre be applied wet and -rubbed till quite dry, increasing the rapidity of the friction -as the moisture evaporates. It must be performed in gloves, -as the vapour from the fingers, as well as the slightest -breath, dims the polished surface effectually. With these -precautions a perfect vitreous polish is easily obtained. -We may here remark, that hardly any two salts can be -polished by the same process. Thus, Rochelle-salt must be -finished wet on the silk, and instantly transferred to soft -bibulous linen and rapidly rubbed dry. Experience alone -can teach these peculiarities, and it is necessary to resort -to contrivances (sometimes very strange ones) for the -purpose of obtaining good polished sections of soft crystals, -especially of those easily soluble in water.</p> - -<p>“The nitre is thus polished on both its surfaces, which -should be brought as near as possible to parallelism.”</p> - -<div class="footnote"> - -<p><a id="Footnote_F" href="#FNanchor_F" class="fnanchor">F</a> Sometimes the saltpetre of the shops is nitrate of <em>soda</em>, and as -this is slightly deliquescent, it is well to be certain that we have the -nitrate of <em>potash</em>, which is free from this defect.</p></div> - -<p>Some sections of the naturally formed crystals also show -the “rings” very well,—as Iceland Spar, which gives a -single ring and cross; but the difficulty of cutting and -polishing them is almost too great for the amateur, and -must be left to the lapidary. This curious phenomenon, -however, may be seen by using a plate of ice uninterruptedly -formed of about one inch in thickness.</p> - -<p><span class="pagenum" id="Page_111">111</span> -Before concluding these remarks on sections, I must mention -a few difficulties which may be met with, and their -remedies. The foremost of these is the softness of some -objects, which have not resistance enough in themselves to -bear cutting even with the sharpest instruments. This -may often be removed by soaking in a solution of gum, and -then drying, which will render the substance firm enough -to be cut, when the sections must be steeped in water, and -the gum thus got rid of. Small seeds, &c., may be placed -in wax when warmed, and will be held firmly enough when -it is again cold to allow of them being cut into sections, &c. -And, lastly, where a substitute for a microscopist’s hand-vice -is required, a cork which fits any tube large enough may be -taken and split, the object being then placed between the -two parts, and the cork thrust into the tube, a sufficient -degree of firmness will be obtained to resist any necessary -cutting, &c.</p> - -<p><span class="smcap">Dissection.</span>—As I stated at the commencement of this -chapter, no written instructions can enable any student to -become an adept in this branch without much experience -and no little study. I will, however, describe the necessary -apparatus, and afterwards mention the mode of treatment -which certain objects require.</p> - -<p>A different microscope is manufactured for the purpose of -dissection, most first-rate makers having their own model. -The object-glasses of many of these are simple, and consequently -not expensive; but one of the great requisites is a -stage large enough to hold the trough, in which the operation -is often performed. Where this is the case it would scarcely -be worth the expense of getting a dissecting microscope if -the student were pursuing no particular study, but merely -made use of the instrument when an object to be operated -upon turned up accidentally. The ordinary form is much -improved for this purpose, by having two wooden rests -placed at the sides of the microscope, upon which the hands -may be supported when working upon the stage. These -should be weighty enough to be free from danger of moving.<span class="pagenum" id="Page_112">112</span> -These supports will also be found to be a remedy against much -of the weariness which inevitably arises from having to -sustain the hands as well as work with them. The erector, -as I before observed, is necessary to a young student; but -with a little practice he may work very well without it.</p> - -<p>We will now notice some of the instruments which are -most useful in dissection. Two or three different sizes of -ordinary scissors should be possessed, but the shapes -must be modified in others for many purposes, as those -used by surgeons; a pair with the cutting parts bent in a -horizontal direction, and another pair slightly curved in a -perpendicular; so that parts of the substance operated upon -may be reached, which it would be impossible to touch with -straight scissors. One point of these is sometimes blunt, -and the other acute, being thus made very useful in -opening tubular formations. Another form of these is made, -where the blades of the scissors are kept open by a spring, -the handles being pressed together by the fingers. Where -it is desirable, one or both of these handles may be lengthened -to any degree by the addition of small pieces of wood.</p> - -<p><span class="smcap">The Knives</span> which are most useful are those of the -smallest kind which surgeons employ in very delicate operations. -These are made about the length of an ordinary pen-knife, -and are fixed in rather long flattish handles; some -are curved inwards, like the blade of a scythe, others backwards; -some taper to a point, whilst others again are broad -and very much rounded. Complete boxes are now fitted up -by the cutlers, of excellent quality and surprisingly cheap.</p> - -<p><span class="smcap">Needles.</span>—These are very useful and should be firmly -fixed in handles as recommended in <a href="#CHAPTER_I">Chapter I.</a> It is -convenient to have them of various lengths and thicknesses. -If curved by heating and bending to any required shape -they may be re-hardened by putting them whilst hot into -cold water. Dr. Carpenter also makes edged instruments by -rubbing down needles upon a hone. They are more -pleasant to work with when <em>short</em>, as the spring they have -whilst <em>long</em> robs them of much of their firmness.</p> - -<p><span class="pagenum" id="Page_113">113</span> -A <em>glass syringe</em> is also useful in many operations, -serving not only to cleanse the objects but to add or -withdraw liquids from the <em>dissecting-trough</em>. This trough -will now be described, as many substances are so changed -by becoming dry that it is impossible to dissect them -unless they are immersed in water during the operation. -If the object is opaque and must be worked by reflected -light, a small square trough may be made to the required -size of gutta-percha, which substance will not injure the -edge of the knives, &c.; but where transparency is -necessary, a piece of thin plate-glass must be taken, and by -the aid of marine glue (as explained in <a href="#CHAPTER_IV">Chapter IV.</a>) the -sides affixed of the required depth. As pins, &c., cannot be -used with the glass troughs and the substance must be kept -extended, a thin sheet of cork loaded with lead in order to -keep it under water may be used; but this, of course, renders -the bottom opaque. When working with many thin substances, -a plate of glass three or four inches long and two -wide will serve every purpose, and be more pleasant to use -than the trough. A drop or two of water will be as much -liquid as is needed, and this will lie very well upon the flat -surface. As these are the principal apparatus and arrangements -which are requisite in dissection, the method of -proceeding in a few cases may now be noticed.</p> - -<p><span class="smcap">Vegetables.</span>—The dissection of vegetable matter is much -less complicated than that of animal; maceration in water -being a great assistant, and in many cases removing all -necessity for the use of the knife. This maceration may be -assisted by needles, and portions of the matter which are not -required may be removed by them. When, for instance, -the spiral vessels which are found in rhubarb are wanted, -some parts containing these are chosen and left in a small -quantity of water until the mass becomes soft, and this -is more quickly effected when the water is not changed. -The mass must be then placed upon a glass plate when practicable, -or in the trough when large, and with the aid of two -needles the matter may be removed from the spiral vessels,<span class="pagenum" id="Page_114">114</span> -which are plainly seen with a comparatively low power; and -by conveying these to a clean slip of glass, repeating the -process, and at last washing well, good specimens may be procured. -Most of these should be mounted in some of the preservative -liquids in the manner described in <a href="#CHAPTER_IV">Chapter IV.</a> -Many, however, may be dried on the slide, immersed in -turpentine, and then mounted in balsam; but liquid is -preferable, as it best preserves the natural appearance. -Certain kinds of vegetables require a different treatment to -separate these spiral vessels. Asparagus is composed of -very hard vegetable matter, and some have recommended -the stems to be first boiled, which will soften them to such a -degree that they may easily be separated. Dilute acids are -also occasionally used to effect this; and in some instances to -obtain the <i xml:lang="la" lang="la">raphides</i> caustic potash may be employed; but after -<em>any</em> of these agents have been made use of, the objects must -be thoroughly cleansed with water, else the dissecting -instruments (and perhaps the cell) will be injured by the -action of the remaining portion of the softening agent.</p> - -<p>For the dissection of <em>animal tissues</em> it is necessary that -the instruments be in the best order as to sharpness, &c.; -and as the rules to be observed must necessarily be somewhat -alike in many instances, the treatment required by -some of the objects most frequently mounted will now be -described. We may here remark that <em>cartilage</em> can be best -examined by taking sections, which will show the arrangement -of the cells very perfectly. This, however, is plainly -seen in the mouse’s ear without any section being necessary. -Glycerine, the preservative liquids before mentioned, and -Canada balsam are all used to mount it; but perhaps -the first named may be preferred in many cases.</p> - -<p><span class="smcap">Muscle.</span>—This is what is commonly called the “flesh” -of animals. If a piece be laid upon the slide under the -microscope, bundles of “fibres” will be perceived, which -with needles and a little patience may be separated into -portions, some of these being “striated,” or marked with -alternate spaces of dark and light. Some of the <em>non-striated</em><span class="pagenum" id="Page_115">115</span> -or <em>smooth</em> class of muscle, such as is found in -intestines, may be prepared for the microscope by immersing -for a day or two in nitric acid diluted with three or four -parts of water, and then separating with needles and mounting -as soon as possible. Sometimes <em>boiling</em> is resorted to -to facilitate the separation, and occasions little or no alteration -in the material. Specimens are often taken from the -<em>frog</em> and the <em>pig</em>, as being amongst the best, <em>Goadby’s -solution</em> being generally used in mounting them. The -muscle of insects also shows the striæ very perfectly.</p> - -<p><span class="smcap">Nerve-tissue.</span>—This is seldom mounted; as Dr. Carpenter -observes, “no method of preserving the nerve-tissue has -been devised which makes it worth while to mount preparations -for the sake of displaying its minute characters,” -but we will mention a few particulars to be observed in its -treatment. The nerve should be taken from the animal as -soon as possible after death, and laid upon a glass slide, -with a drop or two of serum if possible. The needles may -be used to clean it, but extreme delicacy is necessary. It -will be found that the nerve is tubular and filled with a -substance which is readily ejected by very slight pressure. -When the nerve is submitted to the action of acetic acid, -the outer covering, which is very thin, is considerably contracted, -whilst the inner tube is left projecting; and thus is -most distinctly shown the nature of the arrangement. Mr. -Lockhart Clarke, who has made great researches into the -structure of the spinal cord, gives a part of his experience -as follows:—He takes a perfectly fresh spinal cord and -submits it to the action of strong spirits of wine. This -gives the substance such a degree of hardness that thin -sections may be readily cut from it, which should be placed -upon a glass in a liquid consisting of three parts of spirit -and one of acetic acid, which renders them very distinct. -To mount these sections, they must now be steeped in pure -spirit for two hours and afterwards in oil of turpentine, -and lastly must be mounted in Canada balsam.</p> - -<p><span class="smcap">Tracheæ of Insects, &c.</span>—The nature of these<span class="pagenum" id="Page_116">116</span> -was described in <a href="#CHAPTER_III">Chapter III.</a>, but the method of procuring -them was not explained, as this clearly belongs to -“dissection.” The larger tubes are readily separated by -placing the insect in water, and fixing as firmly as possible, -when the body must be opened and the viscera removed. -The tracheæ may then be cleaned by the aid of a camel-hair -pencil, and floated upon a glass, where they must first be -allowed to dry, and then be mounted in balsam. Mr. Quekett -gives the following method of removing the tracheæ from the -larva of an insect:—“Make a small opening in its body, -and then place it in strong acetic acid. This will soften -or decompose all the viscera, and the tracheæ may then be -well washed with the syringe, and removed from the body -with the greatest facility, by cutting away the connections -of the main tubes with the spiracles by means of fine-pointed -scissors. In order to get them upon the slide, it -must be put into the fluid, and the tracheæ floated upon it; -after which they may be laid out in their proper position, -then dried and mounted in balsam.” If we wish them to -bear their <em>natural</em> appearance, they must be mounted in a -cell with Goadby’s fluid; but the structure is <em>sometimes</em> -well shown in specimens mounted dry. As before mentioned, -these tracheæ terminate on the outside in openings -termed spiracles, which are round, oblong, and of various -shapes. Over these are generally a quantity of minute -hairs, forming a guard against the entrance of dust, &c. -The forms of these are seldom alike in two different kinds -of insects, so that there is here a wide field for the student. -The dissection, moreover, is very easy, as they may be cut -from the body with a sharp knife or scissors, and mounted -in balsam or fluid. Many of the larvæ afford good specimens, -as do also some of the common Coleopterous insects.</p> - -<p><span class="smcap">Tongues, or Palates, of Molluscs.</span>—Of the nature of -these, Dr. Carpenter gives the following description:—“The -organ which is commonly known under this designation is -one of a very singular nature; and we should be altogether -wrong in conceiving of it as having any likeness to that on<span class="pagenum" id="Page_117">117</span> -which our ordinary ideas of such an organ are founded. -For, instead of being a projecting body, lying in the cavity -of the mouth, it is a tube that passes backwards and downwards -beneath the mouth, its higher end being closed, -whilst in front it opens obliquely upon the floor of the -mouth, being, as it were, slit up and spread out so as to -form a nearly flat surface. On the interior of the tube, as -well as on the flat expansion of it, we find numerous transverse -rows of minute teeth, which are set upon flattened -plates; each principal tooth sometimes having a basal plate -of its own, whilst in other instances one plate carries -several teeth.” These palates, or tongues, differ much -amongst the Gasteropods in form and size, some of them -being comparatively of an immense length. Many are -amongst the most beautiful objects when examined with -polarized light. They must, however, be procured by dissection, -which is usually performed as follows:—The animal -is placed on the cork in the dissecting-trough before mentioned, -and the head and forepart cut open, spread out, and -firmly pinned down. With the aid of fine scissors or knife, -the tongue must be then detached from its fastenings, and -placed in water for a day or two, when all foreign matter may -with a little care be removed. In what way it should be -mounted will depend on the purpose for which it is intended. -If for examination as an ordinary object, it may be laid -upon the slide and allowed to dry, which arrangement will -show the teeth very well. If we wish to see it as it is naturally, -it must be mounted in a cell with Goadby’s fluid; but -if it is wanted as a polarizing object, it must be floated upon -a slide, allowed to dry thoroughly, and then Canada -balsam added in the usual manner.</p> - -<p>In the stomach, also, of some of these molluscs teeth are -found, which are very interesting objects to examine, and -must be dissected out in the same manner as the -“tongues.”</p> - -<p>Since writing the above. Dr. Alcock (whose very beautiful -specimens prove him to be a great authority in this<span class="pagenum" id="Page_118">118</span> -branch) has published some of his experience in the second -volume of the third series of “Memoirs of the Literary -and Philosophical Society of Manchester.” By his permission -I make the following <span class="locked">extract:—</span></p> - -<p>“This closes my present communication on the tongues -of mollusca; but as some members may possibly feel -inclined to enter upon the inquiry themselves, I think -it will not be amiss to add a few remarks on the manner -in which they are to be obtained.</p> - -<p>“First, as to the kinds best worth the trouble of preparation. -Whelks, Limpets, and Trochuses should be taken -first. Land and fresh-water snails can scarcely be recommended, -except as a special study,—their tongues being -rather more difficult to find, and the teeth so small that -they require a high power to show them properly. It -would appear, from Spallanzani’s description of the anatomy -of the head of the snail, that even he did not make out -this part, although, in his curious observations on the reproduction -of lost parts, he must have carefully dissected -more snails than any other man.</p> - -<p>“As to preserving the animals till wanted, they should -simply be dropped alive into glycerine or alcohol. Glycerine -is perhaps best where only the tongues are wanted; -but it leaves the animals very soft; and as it does not -harden their mucus at all, they are very slippery and -difficult to work upon when so preserved.</p> - -<p>“Then as to the apparatus required for dissection. In the -first place, all the work is to be done under water, and a -common saucer is generally the most convenient vessel -to use. No kind of fastening down or pinning out of the -animal is needed; and, in fact, it is much better to have -it quite free, that you may turn it about any way you wish. -The necessary instruments are a needle-point, a pair -of fine-pointed scissors, and small forceps; the forceps -should have their points slightly turned in towards -each other.</p> - -<p>“A word or two on the lingual apparatus generally,<span class="pagenum" id="Page_119">119</span> -and on its special characters in a few different animals, -will conclude what I have to say.</p> - -<p>“The mode of using the tongue can be easily seen in -any of the common water-snails, when they are crawling -on the glass sides of an aquarium; it may then be observed -that from between the fleshy lips a thick mass is -protruded, with a motion forwards and upwards, and afterwards -withdrawn, these movements being almost continually -repeated. The action has the appearance of licking; but -when the light falls suitably on the protruded structure, -it is seen to be armed with a number of bright points, -which are the lingual teeth, so arranged as to give the -organ the character and action of a rasp.</p> - -<p>“If you proceed to dissection, and open the head of one -of these mollusca (say, for instance, a common limpet), you -will find the cavity of the mouth almost filled with the -thick fleshy mass, the front of which is protruded in the -act of feeding; and on its upper surface, extending along -the middle line from back to front, is seen the strong -membranous band upon which the teeth are set. The -mass itself consists of a cartilaginous frame, surrounded -by strong muscles; and these structures constitute the -whole of the active part of the lingual apparatus....</p> - -<p>“But the peculiarity of the toothed membrane, which -makes its name of ‘<em>ribbon</em>’ so appropriate, is, that there -is always a considerable length of it behind the mouth, -perfectly formed, and ready to come forward and supply -the place of that at the front, which is continually wearing -away by use.</p> - -<p>“In the limpet this reserve-ribbon is of great length, -being nearly twice as long as the body, and the whole -of it is exposed to view on simply removing the foot of -the animal; nothing, then, can be easier than to extract -the tongue of the common limpet. But, unfortunately, -what you find in one kind of mollusc is not at all what -you find in another. In the Acmæas, for instance, which -are very closely related to the limpets, and have shells<span class="pagenum" id="Page_120">120</span> -which cannot be distinguished, the reserve portion of the -ribbon has to be dug out from the substance of the liver, -in which it is imbedded, that organ being, as it were, -stitched completely through by a long loop of it.... -It might be thought a comfortable reflection that, at all -events, one end of the ribbon can always be found in the -mouth; but in many cases this is about the worst place -to look for it. Perhaps it may appear strange that in -some of the smaller species, with a retractile trunk, a -beginner may very likely fail altogether in his attempt to -find the mouth; if, however, the skin of the back is removed, -commencing just behind the tentacles, there will be -very little difficulty in making out the trunk, which either -contains the whole of the ribbon, as in the whelk, or the -front part of it, as in <i xml:lang="la" lang="la">Purpura</i> and <i xml:lang="la" lang="la">Murex</i>, where a free -coil is also seen to hang from its hinder extremity.... -In the periwinkles the same plan of proceeding, by at once -opening the back of the animal, is best; and on doing so, -the long ribbon, coiled up like a watch-spring, cannot fail -to be found.</p> - -<p>“In the Trochuses, and indeed in all the <i xml:lang="la" lang="la">Scutibranchiata</i>, -one point of the scissors should be introduced into the -mouth of the animal, and an incision made directly backwards -in the middle line above to some distance behind the -tentacles; the tongue is then immediately brought into -view, lying along the floor of the mouth.”</p> - -<p>Dr. Alcock’s method of dissection will be found to differ -in some degree from the general rules before given; and -when the tongue is dissected out he washes it for one hour -(shaking it now and then) in a weak solution of potash. -After cleaning thoroughly in water, it must be mounted by -one of the methods before mentioned.</p> - -<p>Amongst insects, especially the grasshopper tribe, are -found many which possess a gizzard, armed with strong -teeth, somewhat similar to those of the molluscs. It -requires great nicety of manipulation to obtain these for -the microscope; but it would be useless to attempt any<span class="pagenum" id="Page_121">121</span> -description of the process here, as the strident can only be -successful by experience in dissecting objects less difficult -to manage, and by using the most delicate instruments.</p> - -<p>We have now considered most of those objects which -require any <em>peculiar</em> treatment in section-cutting, &c.; but -in no branch of microscopic manipulation is experience -more necessary than in this.</p> - -<hr /> - -<p><span class="pagenum" id="Page_122">122</span></p> - -<div class="chapter"> -<h2 id="CHAPTER_VI" class="vspace"><span class="gesperrt">CHAPTER VI</span>.<br /> - -<span class="subhead">INJECTION.</span></h2> -</div> - -<p class="in0"><span class="firstword">1.</span> Injection is the filling of the arteries, veins, or other -vessels of animals with some coloured substance, in order -that their natural arrangement may be made visible. -This is, of course, a delicate operation, and needs special -apparatus, which I will now attempt to describe.</p> - -<p>2. <em>Syringe.</em>—This is usually made to contain about -two ounces. On each side of the part next to the -handle is a ring, so that the finger may be thrust through -it, and the thumb may work the piston as in an ordinary -syringe. The plug of the piston must be “packed” with -wash-leather, and fit so closely as to be perfectly air-tight; -and if, when it has been used awhile, it is found that -some of the liquid escapes past the plug into the back part -of the body, it must be <em>repacked</em>, which operation will be -best understood by examining the part. These syringes -are made of various sizes, but in ordinary operations the above -will be all that is needed. The <em>nozzle</em> is about an inch long, -and polished so accurately that there is no escape when -the <em>pipes</em> are tightly placed upon it <em>dry</em>.</p> - -<p>3. The <em>pipes</em> are usually about an inch long, to the end -of which are affixed thicker tubes so as to fit the nozzle, as -before mentioned, whilst a short arm projects from each -side of these, so that the silk or thread which is used to tie -this artery, &c., upon the thin pipe may be carried round -these arms, and all danger of slipping off prevented. The -<em>pipes</em> are made of different sizes, from that which will -admit only a very fine needle (and this will need now and -then to be cleaned, or to be freed from any chance obstruction),<span class="pagenum" id="Page_123">123</span> -to that which will take a large pin. These sizes must -always be at hand, as the vessels of some subjects are -exceedingly minute.</p> - -<p>4. <em>Stopcock.</em>—This is a short pipe like a small <em>straight</em> -tap, which fits accurately upon the end of the syringe like -the pipes, and also takes the pipes in the same manner. -The use of this is absolutely necessary when the object is -so large that one syringe full of liquid will not fill it. If -no preventive were used, some part of the liquid would return -whilst the syringe was being replenished, but the stopcock -is then turned as in an ordinary tap, and all danger of this -effectually removed.</p> - -<p>5. <em>Curved needles.</em>—These are easily made by heating -common needles at the end where the eye is situated, and -bending them with a small pair of “pliers” into a segment -of a circle half an inch in diameter. They are, perhaps, more -convenient when the bent part is thrown slightly back -where it commences. The pointed end is then thrust into -a common penholder, and the needle needs no re-tempering, -as the work for which it is wanted is simply to convey the -thread or silk <em>under</em> any artery or vessel where it would be -impossible to reach with the unassisted fingers.</p> - -<p>6. A kind of <em>forceps</em>, commonly know by the name of -“bullnose forceps,” will be constantly required during the -process of injecting. These are short, usually very strong, -but not heavy, and close very tightly by their own spring, -which may be easily overcome and so released by the -pressure of the fingers. When any vessel has not been -tied by the operator, and he finds the injected fluid -escaping, one of these “bulldogs” may be taken up and -closed upon the opening. This will cause very little interruption, -and the stoppage will be almost as effectual as -if it were tied.</p> - -<p>7. When the ordinary mode of injection is employed, it -is necessary that the preparations be kept warm during -the time they are used, otherwise the gelatine or size which -they contain becomes stiff, and will not allow of being<span class="pagenum" id="Page_124">124</span> -worked by the syringe. For this purpose we must procure -small earthenware or tin pots of the size required, which -will differ according to the kind of work to be done; and to -each of these a loose lid should be adapted to protect it -from dust, &c. These pots must be allowed to stand in -a tin bath of water, under which a lamp or gas flame -may be placed to keep the temperature sufficiently high -to insure the perfect fluidity of the mixture. The tin -bath is, perhaps, most convenient when made like a small -shallow cistern; but some close it on the top to place -the pots upon it, and alter the shape to their own convenience.</p> - -<p>8. We will now inquire into some of the materials which -are needed in this operation; the first of which is <em>size</em>. -This substance is often used in the form of <em>glue</em>, but it -must be of the very best and most transparent kind. To -make the liquid which is to receive the colours for the -usual mode of injecting, take of this glue seven ounces, and -pour upon it one quart of clean water; allow this to stand -a few hours, and then boil gently until it is thoroughly -dissolved, stirring with a wooden or glass rod during the -process. Take all impurities from the surface, and strain -through flannel or other fine medium. The weather affects -this a little as to its stiffness when cold, but this must be -counteracted by adding a little more glue if found too -liquid.</p> - -<p>9. Instead of glue, gelatine is generally used, especially -when the work to be accomplished is of the finer -kind. The proportions are very different in this case, -one ounce of gelatine to about fourteen ounces of water -being sufficient. This, like glue, must be soaked a few -hours in a small part of the cold water, the remainder -being boiled and added, when it must be stirred until -dissolved. A good size may be made by boiling clean -strips of parchment for awhile, and then straining the -liquid whilst hot through flannel; but when the injections -are to be <em>transparent</em>, it is of the greatest importance that<span class="pagenum" id="Page_125">125</span> -the size be as colourless as possible. For this purpose -good gelatine must be employed, as Nelson’s or Cox’s: some -persons of experience prefer the latter.</p> - -<p>10. <em>Colours.</em>—The size-solution above mentioned will -need some colouring matter to render it visible when -injected into the vessels of any animal, and different colours -are used when two or more kinds of vessels are so treated, -in order that each “set” may be easily distinguished by -sight. The proportion in which these colours are added to -the size-solution may be given as <span class="locked">follows:—</span></p> - -<p>11. <span class="locked">For—</span></p> - -<table summary="colouring solutions"> - <tr> - <td class="tdl">Red</td> - <td class="tdc"> 8</td> - <td class="tdc">parts of size-solution (by weight) to</td> - <td class="tdc">1</td> - <td class="tdc">part of </td> - <td class="tdl">vermilion.</td></tr> - <tr> - <td class="tdl">Yellow</td> - <td class="tdc"> 6</td> - <td class="tdc">” <span class="in2">”</span></td> - <td class="tdc">1</td> - <td class="tdc">”</td> - <td class="tdl">chrome yellow.</td></tr> - <tr> - <td class="tdl">White</td> - <td class="tdc"> 5</td> - <td class="tdc">” <span class="in2">”</span></td> - <td class="tdc">1</td> - <td class="tdc">”</td> - <td class="tdl">flake-white.</td></tr> - <tr> - <td class="tdl">Blue</td> - <td class="tdc"> 3</td> - <td class="tdc">” <span class="in2">”</span></td> - <td class="tdc">1</td> - <td class="tdc">”</td> - <td class="tdl">blue-smalt, fine.</td></tr> - <tr> - <td class="tdl">Black</td> - <td class="tdc">12</td> - <td class="tdc">” <span class="in2">”</span></td> - <td class="tdc">1</td> - <td class="tdc">”</td> - <td class="tdl">lamp-black.</td></tr> -</table> - -<p class="in0">Whichever of these colours is made use of must be levigated -in a mortar with the addition of a very small quantity of -water until every lump of colour or foreign matter is reduced -to the finest state possible, otherwise in the process of injecting -it will most likely be found that some of the small channels -have been closed and the progress of the liquid stopped. -When this fineness of particles is attained, warmth sufficient -to render the size quite fluid must be used, and the colour -added gradually, stirring all the time with a rod. It may -be here mentioned that where one colour only is required, -vermilion is, perhaps, the best; and blue is seldom used -for opaque objects, as it reflects very little more light than -black.</p> - -<p>12. When it is wished to fill the capillaries (the minute -vessels connecting the arteries with the veins), the “Micrographic -Dictionary” recommends the colouring matter to be -made by double decomposition. As a professed handbook -would be, perhaps, deemed incomplete without some directions<span class="pagenum" id="Page_126">126</span> -as to the mode of getting these colours, I will here -make use of those given in that work. For red, however, -vermilion, as above stated, may be used; but it must be -carefully examined by reflected light to see whether it be free -from all colourless crystals or not. It must first be worked in -a mortar, and then the whole thrown into a quantity of -water and stirred about; after leaving it not longer than -a quarter of a minute, the larger portions will settle to -the bottom, and the liquid being poured off will contain the -finer powder. This may then be dried slowly, or added to -the size whilst wet in the manner before advised.</p> - -<p>13. <em>Yellow injection.</em>—To prepare this, <span class="locked">take—</span></p> - -<table class="narrow20" summary="yellow injection"> - <tr> - <td class="tdl">Acetate (sugar) of lead</td> - <td class="tdl">380 grains.</td></tr> - <tr> - <td class="tdl">Bichromate of potash</td> - <td class="tdl">152 <span class="in1">”</span></td></tr> - <tr> - <td class="tdl">Size</td> - <td class="tdl"> 8 ounces.</td></tr> -</table> - -<p class="in0">Dissolve the lead salt in the warm size, then add the bichromate -of potash finely powdered.</p> - -<p class="p2">Some of the chromic acid remains free, and is wasted in -this solution, so the following is <span class="locked">given:—</span></p> - -<table class="narrow20" summary="yellow injection variation"> - <tr> - <td class="tdl">Acetate of lead</td> - <td class="tdl">190 grains.</td></tr> - <tr> - <td class="tdl">Chromate of potash (neutral)</td> - <td class="tdl">100 <span class="in1">”</span></td></tr> - <tr> - <td class="tdl">Size</td> - <td class="tdl"> 4 ounces.</td></tr> -</table> - -<p class="in0">The first of these has the deepest colour, and is the most -generally used.</p> - -<p>14. <em>White injection.</em>—This is a carbonate of <span class="locked">lead:—</span></p> - -<table class="narrow20" summary="white injection"> - <tr> - <td class="tdl">Acetate of lead</td> - <td class="tdl">190 grains.</td></tr> - <tr> - <td class="tdl">Carbonate of potash</td> - <td class="tdl"> 83 <span class="in1">”</span></td></tr> - <tr> - <td class="tdl">Size</td> - <td class="tdl"> 4 ounces.</td></tr> -</table> - -<p class="in0">Dissolve the acetate of lead in the warm size, and filter -through flannel; dissolve the carbonate of potash in the -smallest quantity of water, and add to the size: 143 grains -of carbonate of soda may be substituted for the carbonate of -potash.</p> - -<p><span class="pagenum" id="Page_127">127</span> -15. For blue injection, which is not, however, much used -with reflected light, as before stated, <span class="locked">take—</span></p> - -<table class="narrow20" summary="blue injection"> - <tr> - <td class="tdl">Prussian blue</td> - <td class="tdl">73 grains.</td></tr> - <tr> - <td class="tdl">Oxalic acid</td> - <td class="tdl">73 <span class="in1">”</span></td></tr> - <tr> - <td class="tdl">Size</td> - <td class="tdl"> 4 ounces.</td></tr> -</table> - -<p class="in0">The oxalic acid is first finely powdered in a mortar, the -Prussian blue and a little water added, and the whole then -thoroughly mixed with the size.</p> - -<p>16. It may here be repeated, that it is only when the capillaries -are to be filled that there is any need to be at the trouble -to prepare the colours by this double decomposition; and, -indeed, colours ground so finely may be procured that the -above instructions would have been omitted, had it not been -supposed that some students might find a double pleasure -in performing as much of the work as possible by their own -unaided labours.</p> - -<p>17. The process of injection may now be considered; but -it is impossible for written instructions to supply the place of -experience. I will do my best, however, to set the novice at -least in the right way. There are two kinds of injection—one -where the object and colours are opaque, and consequently -fit for examination by <em>reflected</em> light only; the -other, where the vessels are filled with transparent colours, -and must be viewed by <em>transmitted</em> light. The first of these -is most frequently employed, so we will begin with it. In -the object which is to be injected a vessel of the kind which -we wish to be filled must be found; an opening must then -be made in it to allow one of the small pipes before mentioned -to be thrust some distance within it. When this is -accomplished, thread the curved needle with a piece of silk -thread, or very fine string, which some operators rub well -with beeswax. This thread must not be too thin, else there -is danger of cutting the vessel. The cord is then carried -under the inserted pipe, and the vessel bound tightly upon -it, the ends being brought up round the transverse arms, -and there tied; so that all danger of accidentally withdrawing<span class="pagenum" id="Page_128">128</span> -the pipe is obviated. Care must now be used in -closing all the vessels which communicate with that where -the pipe is placed lest the injecting fluid escape; and this -must be done by tieing them with silk. Should, however, -any of these be left open by accident, the bullnose forceps -must be made use of, as before recommended.</p> - -<p>18. The part to be injected must now be immersed in -warm water, not, however, above 100° Fahrenheit, and be -left until the whole is thoroughly warmed. Whilst this is -being done, the coloured size must be made ready by the pot -being placed in the tin bath of warm water, which must be -of sufficient temperature (about 110° Fahrenheit) to keep it -perfectly liquid. For the same purpose, the syringe is often -tightly covered with two or three folds of flannel; and, -indeed, there is no part of the process which requires more -attention. If the substance to be injected is too hot, it is -injured; whilst, if any of the articles are too cold, the gelatine, -or size, loses a part of its fluidity, and consequently -cannot enter the minute parts. When all is prepared, the -syringe, with the stopcock attached, should be warmed, and -then filled and emptied with the injecting fluid two or three -times, care being taken that the end of the syringe be kept -beneath any bubbles which form upon the surface. The -syringe may then be filled, and closely attached to the pipe -which is tied in the vessel. With a firm and steady pressure -the piston must be forced downwards, when the substance -will be perceived to swell, and the colour show itself in places -where the covering is thin. When the syringe is <em>almost</em> -emptied of its contents, the stopcock must be turned to prevent -any escape of the injection from the subject. It must then be -refilled, as in the first instance, and the process repeated. I -say <em>almost emptied</em>, because it is well not to force the piston -of the syringe quite to the bottom, lest the small quantity -of air which frequently remains be driven into some of the -vessels, and the object be injured or quite ruined. As the -injection is proceeded with, it will be found that the force -required grows greater, yet care must be taken not to use<span class="pagenum" id="Page_129">129</span> -too much, or the vessels will burst, and render all the labour -fruitless. The movement of the piston must be occasionally -so slow as to be almost imperceptible, and for this reason it is -sometimes marked with lines about one-eighth of an inch -apart.</p> - -<p>19. Of course, during the whole process the injecting -fluid and subject must be kept at a temperature high enough -to allow the liquid to flow freely; and the escape of a little -of it need cause no fears to the student, as it is almost impossible -to fill any subject without some loss. When the -injected object has received sufficient fluid, it should have a -plump appearance, owing to all the vessels being well filled. -The vessel must then be tied up where the pipe was inserted, -and the whole left in cold water two or three hours, after -which time it may be mounted; but it may be well to notice -a few things which the beginner ought to know before entering -into that part of the process; and he may be here informed -that it is not necessary to mount the objects immediately, -otherwise it would be impossible for one person to make -use of half of any large subject, as it would be in a state -of decay long before each part could have been examined -and separated. Large pieces should be therefore immersed -in equal parts of spirits of wine and water, or -glycerine, which some think better still, and thus preserved -in bottles until time can be given to a closer examination.</p> - -<p>20. In operating upon large subjects, entire animals, -&c., the constant pressure required by the piston of the -syringe grows wearisome, besides occupying both hands, -which is sometimes inconvenient when working without -assistance. To obviate this, another way of driving the -syringe was published in the “Micrographic Dictionary” -which I will quote here:—“We have therefore contrived a -very simple piece of apparatus, which any one can prepare -for himself, and which effects the object by mechanical -means. It consists of a rectangular piece of board, two feet -long and ten inches wide, to one end of which is fastened an<span class="pagenum" id="Page_130">130</span> -inclined piece of wood (equal in width to the long board, -and one foot high). The inclined portion is pierced with -three holes, one above the other, into either of which the -syringe may be placed—the uppermost being used for the -larger, the lowermost for the smaller syringe; and these -holes are of such size as freely to admit the syringe covered -with flannel, but not to allow the rings to pass through -them. The lower part of the syringe is supported upon a -semiannular piece of wood, fastened to the upper end of an -upright rod, which slides in a hollow cylinder fixed at its -base to a small rectangular piece of wood; and by means of -a horizontal wooden screw, the rod may be made to support -the syringe at any height required. The handle of the -syringe is let into a groove in a stout wooden rod connected -by means of two catgut strings with a smaller rod, to the -middle of which is fastened a string playing over a pulley, -and at the end of which is a hook for supporting weights, -the catgut strings passing through a longitudinal slit in the -inclined piece of wood.” When in use the syringe is filled -with injecting fluid, and passed through one of the three -holes which is most suitable. The object being placed so -that the pipe and syringe can be best joined, the rod -and strings are set in order, and a weight placed on -the hook. The stopcock must then be opened gradually, -when the operator will be able to judge whether the weight -is a proper one or not: if the piston is driven with any -speed, there is danger of injuring the subject, and less -weight may be used; if, however, the piston does not move, -more must be added.</p> - -<p>21. Such is the method recommended by the “Micrographic -Dictionary,” and perhaps it is as good as any -mechanical plan could be; but where the operator is willing -to undergo the labour of performing all this with the hand, -he has a much better chance of succeeding, because the -pressure can be regulated so accurately, and changed so -quickly when requisite, that no mere machine can compete -with it, however well contrived.</p> - -<p><span class="pagenum" id="Page_131">131</span> -22. When the beginner attempts to inject a subject, one -of his difficulties is finding the vessel from which to commence. -Another consists in distinguishing the arteries -from the veins; but this is partly removed by making a -longitudinal incision in the vessel, and with a blunt thick -needle probing a little distance into the tube. The artery -will be found thicker in the coating than the vein, and the -difference is easily perceived by this mode of testing: the -vein is also of a bluer colour than the artery. I say above, -a “longitudinal incision” must be made: the reason for -this is, the artery when cut across contracts considerably, -and is lost in the adjoining substance; but where the -opening is made <em>longitudinally</em> all danger of this contraction -is obviated.</p> - -<p>23. The different systems of vessels are often injected -with various colours, so that their relative positions, &c., -may be shown most clearly. In some specimens, the veins -are injected with white, and the arteries with red; in the -kidney, the urinary tubes are often filled with white, and -the arteries with red. Then, again, the liver affords tubes -for three or four colours. But no written instructions on -this point can benefit the young student, and he must be -content for a while to employ himself with single colours -until he has gained the mechanical skill and the primary -knowledge which are necessary before he can make any -advance.</p> - -<p>24. We will now consider the best methods of <em>mounting</em> -injected objects. They must always be well washed -in water after they have been kept in any preservative -liquid, using a camel-hair pencil to clean the surface if -necessary. Many parts when injected are in masses, such -as the lungs, liver, &c., of animals, and consequently sections -of these must be cut. For this purpose Valentine’s knife -is very convenient, as the thickness can be regulated so -easily; but where the injections are opaque, there is no -need to have the sections very thin. Some few of this -kind undergo comparatively little change in drying, so that<span class="pagenum" id="Page_132">132</span> -the section may be well washed and floated upon the glass -slide in the place desired, where it will dry perfectly and -adhere to it. It must be then moistened with turpentine -and mounted in Canada balsam like other objects. No great -heat should be used with these preparations, as it is very -liable to injure them; and some of the colours seem to -suffer a slight contraction when any great degree of warmth -is applied. There are many objects, however, which -must be seen in the mass to be understood, and, indeed, -lose all their form and beauty in drying, such as certain -parts of the intestines, &c. These must be mounted in -fluid, with the precautions noticed at length in <a href="#CHAPTER_IV">Chapter IV.</a>, -and for this purpose either Goadby’s fluid, the chloride of -zinc solution, or spirit diluted with ten parts of distilled -water, may be employed. It is a good thing, when practicable, -to mount similar objects on two separate slides, -using different preservative liquids, and taking the precaution -of marking each with the kind of liquid employed. -This not only serves as a guide to what is best for certain -subjects, but if one is injured, there will probably be a -good specimen in the other.</p> - -<p>25. It may be here mentioned that many are now mounting -sections of injected substances with the balsam and -chloroform before mentioned, instead of using balsam alone, -and consider that the labour is much lessened thereby.</p> - -<p>26. A description of that mode of injection which is most -generally employed has now been given, but this is not -the only method of effecting our object. A most ingenious -process was invented by M. Doyers, requiring no artificial -warmth, by which many beautiful objects have been prepared. -Make a solution of bichromate of potash, 524 grains -to a pint of water, and throw this into the vessels to be -injected; then take 1,000 grains of acetate of lead dissolved -in half a pint of water, and force this into the same vessels. -A decomposition now takes place in the vessels, and the -yellow chromate of lead is formed. In this decomposition, -however, the acetate of potash also is formed and as this<span class="pagenum" id="Page_133">133</span> -salt has an injurious action upon the cells, Dr. Goadby -recommends nitrate of lead to be used, which preserves -rather than destroys them. He also advises the addition -of two ounces of gelatine dissolved in eight ounces of water, -to eight ounces of the saturated solution of each salt; but -with this addition the hot-water bath would be required to -keep the injecting fluid liquid.</p> - -<p>27. Many of these are best mounted in balsam, in the -same manner as those made in the ordinary way; whilst -others are best shown when preserved in liquids, for which -purpose Goadby’s fluid may be employed.</p> - -<p>28. This mode of making injections with chromate of -lead is deemed by many the best, especially where one -colour only is employed. But it must be allowed that -there is a little more danger of failure where two separate -fluids are used for the same vessels.</p> - -<p>29. We will now consider the best manner of making -<em>transparent</em> injections, which, for many purposes, possess an -undoubted advantage over the opaque ones. But it must -be remembered that there are certain subjects to which no -transparent injection could be applied, as they are too thick -when in their natural state, and cutting would destroy all -that beauty which is shown by the different parts in their -relative adaptation. For those objects, however, which -must be cut into sections to display their wonders, or are -naturally thin—such as some of the finer tissues, livers, -kidneys, &c.—transparency is a great acquisition, and -enables us to understand the arrangement of the vessels -more perfectly. Again, another advantage is the simplicity -of the process; no hot water is needed with some preparations, -either for the subject or the injecting fluid, which -runs into the minute vessels thoroughly and easily, whilst -the cost is small.</p> - -<p>30. For this kind of injection no colour is so commonly -made use of as Prussian blue. It is not a good one, as -was before stated, for any opaque object, as the light -reflected from it appears almost black; yet by transmitted<span class="pagenum" id="Page_134">134</span> -light no colour is more useful, because its distinctness -is equally great by artificial light and ordinary daylight. -The method of preparing this, as given by Dr. Beale, is as -<span class="locked">follows:—</span></p> - -<table class="narrow25" summary="prussian blue"> - <tr> - <td class="tdl">Glycerine</td> - <td class="tdl"> 1 ounce.</td></tr> - <tr> - <td class="tdl">Wood naphtha, or pyroacetic acid</td> - <td class="tdl"> 1½ drachm.</td></tr> - <tr> - <td class="tdl">Spirits of wine</td> - <td class="tdl"> 1 ounce.</td></tr> - <tr> - <td class="tdl">Ferrocyanide (yellow prussiate) of potash</td> - <td class="tdl">12 grains.</td></tr> - <tr> - <td class="tdl">Tincture of sesquichloride of iron</td> - <td class="tdl"> 1 drachm.</td></tr> - <tr> - <td class="tdl">Water</td> - <td class="tdl"> 4 ounces.</td></tr> -</table> - -<p class="in0">Dissolve the ferrocyanide of potash in one ounce of the -water; add the tincture of sesquichloride of iron to another -ounce. Mix these solutions gradually together, shaking the -bottle well which contains them—it is best to add the iron -to the potash solution. When thoroughly mixed, these -solutions should produce a dark-blue mixture, perfectly -free from any perceptible masses or flocculi. Next mix the -naphtha and spirits of wine, and add the glycerine and the -remaining two ounces of water. This must now be slowly -mixed with the blue liquid, shaking the whole well in a -large bottle whilst the two come together. The tincture of -sesquichloride of iron is recommended, because it can always -be obtained of a uniform strength.</p> - -<p>31. Dr. Turnbull used a mixture slightly different from the -above, which is made with the sulphate of <span class="locked">iron:—</span></p> - -<table class="narrow25" summary="Dr Turnbull's prussian blue"> - <tr> - <td class="tdl">Purified sulphate of iron</td> - <td class="tdl">10 grains.</td></tr> - <tr> - <td class="tdl">Ferrocyanide of potassium</td> - <td class="tdl">32 grains.</td></tr> - <tr> - <td class="tdl">Glycerine</td> - <td class="tdl"> 1 ounce.</td></tr> - <tr> - <td class="tdl">Pyroacetic acid</td> - <td class="tdl"> 1½ drachm.</td></tr> - <tr> - <td class="tdl">Alcohol</td> - <td class="tdl"> 1 ounce.</td></tr> - <tr> - <td class="tdl">Water</td> - <td class="tdl"> 4 ounces.</td></tr> -</table> - -<p class="in0">Dissolve the sulphate of iron in one ounce of the water, -gradually add the ferrocyanide of potassium dissolved in -another ounce, and proceed as above.</p> - -<p><span class="pagenum" id="Page_135">135</span> -32. Dr. Beale also gives us the following carmine injection -to be employed in the same way as the blue.<a id="FNanchor_G" href="#Footnote_G" class="fnanchor">G</a> <span class="locked">Take—</span></p> - -<table class="narrow25" summary="carmine"> - <tr> - <td class="tdl">Carmine</td> - <td class="tdl"> 5 grains.</td></tr> - <tr> - <td class="tdl">Glycerine, with 8 or 10 drops of hydrochloric acid</td> - <td class="tdl">½ ounce.</td></tr> - <tr> - <td class="tdl">Glycerine (pure)</td> - <td class="tdl"> 1 ounce.</td></tr> - <tr> - <td class="tdl">Alcohol</td> - <td class="tdl"> 2 drachms.</td></tr> - <tr> - <td class="tdl">Water</td> - <td class="tdl"> 6 drachms.</td></tr> -</table> - -<p class="in0">Mix the carmine with a few drops of water, and when well -incorporated add about five drops of liquor ammoniæ. To -this dark-red solution about half an ounce of the glycerine is -to be added, and the whole well shaken in a bottle. Next, -very gradually pour in the acid glycerine, frequently shaking -the bottle during admixture. Test the mixture with blue -litmus-paper, and if not of a very decidedly acid reaction, a -few more drops of acid may be added to the remainder of -the glycerine and mixed as before. Lastly, mix the alcohol -and water very gradually, shaking the bottle thoroughly -after adding each successive portion till the whole is mixed. -This fluid may be kept ready prepared, and injections made -very rapidly with it.</p> - -<div class="footnote"> - -<p><a id="Footnote_G" href="#FNanchor_G" class="fnanchor">G</a> When, however, it is desirable to cut very thin sections of the -injected subject, the carmine is sometimes added to a solution of fine -gelatine—gelatine one part to water eight parts. But the warm water -and mode of proceeding which are used with the size solutions before -described will be necessary in this case also.</p></div> - -<p>33. The method of making injections with these colours -is the same as with the gelatine mixtures before described, -except that no heat is required, and consequently most of -the trouble removed. The bottle of the fluid must be well -shaken immediately before use; and when the object is -injected, we must allow it to remain in a cool place for a -few hours before cutting it. Thin sections of the subject -may be cut with Valentine’s knife, as before described, and -are very beautiful transparent objects. Some of the finer -tissues, also, are shown much better by this mode of injection<span class="pagenum" id="Page_136">136</span> -than by the opaque, and are easily mounted by -washing in clean water when first separated, and floating -upon a slide, where they must be allowed to dry -thoroughly. They may then be immediately mounted in -balsam, or kept in the dry state until it is convenient to -finish them; but in many cases this keeping, if too much -prolonged, will injure the object. If it is desired to -transfer the section to another slide, it will be necessary to -wet it thoroughly with water by the aid of a camel-hair -pencil, and then gently strip it off with the forceps. -When it is wished to preserve injected subjects in -“masses,” it must be done by immersion in spirit, and -the sections may be cut at leisure. Most of these transparent -objects may be mounted in Canada balsam; but -some recommend glycerine or glycerine jelly, as allowing -the use of a higher power in their examination, and preserving -them in a more natural form.</p> - -<p>34. A few subjects may be noticed which are very -beautiful when injected, and amongst these are the -eyes of many animals. They must be injected by -the artery in the back part, and when the blue transparent -liquid is employed, nothing can exceed the delicate -beauty which some of the membrane bears. It must, however, -be dissected with care, but well repays us for the -trouble. Water-newts and frogs are not difficult subjects, -and in their skin and other parts are many interesting -objects. Amongst the commoner animals—rats, rabbits, cats, -&c. &c.—almost endless employment may be found, making -use either of portions or the whole animal at once. The -intestines of many of these are very beautiful. We must -divide them with a pair of scissors along the tube, and -cleanse them from all the matter; the coating may then be -laid upon a slide, and any remaining impurity removed -with a camel-hair pencil and water. When dried it may -be mounted in balsam, and having been injected with -the transparent blue, its minute beauty is shown most -perfectly. In injecting a sheep’s foot, which is a good<span class="pagenum" id="Page_137">137</span> -object, the liquid should be forced into it until a slight -paring of the hoof shows the colour in the fine channels -there.</p> - -<p>35. When the lungs of small animals are injected, the -finest fluid must be used, as some of the capillaries are so -small that it is not an easy matter to fill them properly. -And before entering upon these subjects, a certain proficiency -in the mode of using the syringe, &c., should be -obtained by practising upon simpler parts.</p> - -<p>36. No subjects are more difficult to inject than fish, -owing to the extreme softness of their tissues. Dr. Hogg -recommends the tail of the fish to be cut off, and the pipe -to be put into the divided vessel which lies just beneath the -spinal column; by which method beautiful injections may -be made. The gills, however, are the most interesting part -as microscopic objects.</p> - -<p>37. These instructions may seem very imperfect to those -who have had much experience in this branch; but they -will remember that their own knowledge was not gained -from any written descriptions, but was forced upon them -by frequent failures, some of which probably were very disheartening. -As I before stated, it is very difficult (if not -impossible) to accomplish much without some knowledge of -anatomy.</p> - -<p>38. I may here mention that the transparent injections -sent over from the Continent are beautifully executed by -Hyrtl of Vienna (who states that the injected fluid is composed -of gelatine and carmine), Dr. Oschatz of Berlin, -the Microscopic Institute of Wabern, Schaffer and Co. of -Magdeburg, and others. Some of these will bear examining -with a high power. A friend informs me that he measured -a vessel in a rat’s tongue by Hyrtl, which was 1-7200th -of an inch in diameter, and had a clear outline with quarter-inch -objective. He has also made many experiments with -the same materials, but has as yet failed in producing -perfectly distinct outlines, there being a tendency of the -colouring matter (magenta, carmine. &c.) to diffuse itself<span class="pagenum" id="Page_138">138</span> -through the coats of the vessels into the surrounding tissues, -although he has varied the pressure from one half a pound -to sixty pounds. He believes the vessels are first washed -out (injected with warm water and pressure applied), then -some fluid introduced which renders the arteries impervious -to the coloured fluid afterwards injected.</p> - -<p>39. He finds that after washing out the vessels as above, -the injecting fluid is much more easily introduced. He -has used a strong solution of gallic acid previously to injecting -with the colouring matter (in one experiment only), and -the result was satisfactory. He puts the query,—Might not -carbolic acid have a similar effect? He has often used it -with injections to preserve the specimens, but not in sufficient -quantity to act in the way indicated above.</p> - -<p>Since writing the above, Mr. J. G. Dale, F.C.S., and I -have made numerous experiments with carmine injection, -and have at length been favoured with what we deem -success. Some of the vessels in a kitten lately injected do -not exceed 1-2000th of an inch in diameter, and present a -clear outline with one-fifth objective. There is no extra-vasation, -neither does the colouring matter show any grain -except when a very high power is employed. The following -is our <span class="locked">process:—</span></p> - -<table summary="carmine variation"> - <tr> - <td class="tdl w3">Take</td> - <td class="tdl">180 grains best carmine.</td></tr> - <tr> - <td> </td> - <td class="tdl hang3"> ½ fluid ounce of ammonia, commercial strength, viz., 0·92, or 15° ammonia meter.</td></tr> - <tr> - <td> </td> - <td class="tdl hang3"> 3 or 4 ounces distilled water.</td></tr> -</table> - -<p class="in0">Put these into a small flask, and allow them to digest without -heat from twenty-four to thirty-six hours, or until the -carmine is dissolved. Then take a Winchester quart bottle, -and with a diamond mark the spot to which sixteen ounces -of water extend. The coloured solution must be filtered -into the bottle, and to this pure water should be added -until the whole is equal to sixteen ounces.</p> - -<p>Dissolve 600 grains potash alum in ten fluid ounces of -water, and add to this, under constant boiling, a solution<span class="pagenum" id="Page_139">139</span> -of carbonate of soda until a slight permanent precipitate is -produced. Filter and add water up to sixteen ounces. -Boil and add the solution to the cold ammoniacal solution -of carmine in the Winchester quart, and shake vigorously -for a few minutes. A drop of this placed upon white -filtering-paper should show no coloured ring. If much -colour is in solution the whole must be rejected, because, -although it is possible to precipitate all the colouring -matter by the addition of ammonia or alum, it is not well -to do so, as the physical condition of the precipitate is -thereby altered.</p> - -<p>Supposing the precipitation to be complete, or very -nearly so, shake vigorously for at least half an hour, and -allow it to stand until quite cold. The shaking must then -be renewed for some time, and the bottle filled up with pure -water.</p> - -<p>After allowing the precipitate to settle a day, draw off -the clear supernatant fluid with a syphon. Repeat the -washing until the clear liquid gives little or no precipitate -with chloride of barium. So much water must be left -with the colour at last that it shall measure forty fluid -ounces.</p> - -<p>For the injecting fluid take twenty-four ounces of the -above coloured liquid, and three ounces of good gelatine. -Allow these to remain together twelve hours, and then -dissolve by the heat of a water bath; after which it should -be strained through fine muslin.</p> - -<p>As this injecting fluid contains gelatine, the hot water, -and other contrivances mentioned in a former part of the -chapter, will be necessary here also, but no peculiar treatment -will be required.</p> - -<hr /> - -<p><span class="pagenum" id="Page_140">140</span></p> - -<div class="chapter"> -<h2 id="CHAPTER_VII" class="vspace"><span class="gesperrt">CHAPTER VII</span>.<br /> - -<span class="subhead">MISCELLANEOUS.</span></h2> -</div> - -<p class="in0"><span class="firstword">It</span> must be evident to all readers that there are various -objects of interest to the microscopist which cannot be -properly placed amongst any of the forementioned classes, -but must not be omitted in such a guide as this professes -to be. Of these may be mentioned the circulation of the -blood in various animals, the rotary motion of the fluid -in many plants, the best means of taking minute photographs, -&c. &c.</p> - -<p>Perhaps the most interesting of these objects is the circulation -of the blood through the finer vessels of various parts of -the animals made use of for these purposes, which parts, it -is evident, must be very transparent to afford a perfect view -of this phenomenon. The web of the frog’s foot is very -frequently made use of, but requires a certain arrangement, -which we will now describe. A piece of thin wood (Dr. -Carpenter recommends <em>cork</em>) is taken, about eight inches -long and three wide; about an inch from one end is cut -a hole, half or three-quarters of an inch in diameter. The -body of the frog is then placed in a wet bag, or wrapped in -wet calico, whilst the hind-foot projects; the whole is then -laid upon the piece of wood so that the foot, which is left -free, may be extended over the hole. The web must then -be spread out, and secured either by threads to small pins -on the wood, or the pins must be driven through the web -into the wood, and so kept in position. A few bands of -tape must be passed round the body, the leg, and the wood, -to prevent any disarrangement arising from the animal<span class="pagenum" id="Page_141">141</span> -starting, &c. Care must be taken that the tape is not too -tight, else the circulation will be very slow or altogether -stopped. The wood must now be fixed upon the stage, -with the aperture under the object-glass: this is sometimes -done by simply binding it, or a spring is fixed so as to -accomplish the same object without so much trouble. With -a half-inch power the blood may now be seen to flow very -distinctly. The frog may be used for hours if care is taken -to prevent the web from becoming dry, by wetting it with a -little water from time to time. The piece of wood or cork -upon which the frog is laid is often made to give place -to the “frog-plates,” supplied by opticians. These are -made of brass, somewhat resembling the piece of wood -above recommended, but each maker’s pattern differs according -to his own taste.</p> - -<p>The tongue of the frog is also sometimes used for the -purpose of showing the circulation of the blood, which is -done in the following manner:—The body is wrapped -with the calico, and made fast to the plate as before, only -the <em>mouth</em> of the frog is brought to the opening. The -tongue is then gently drawn out of the mouth and pinned -down over the aperture, when the circulation will be well -shown. But, as Dr. Carpenter observes, the cruelty of this -mode of treatment is so repulsive that it is unjustifiable.</p> - -<p>Tadpoles of the frog (which, of course, are only obtainable -in their season) are good subjects for showing the circulation -of the blood. They are best suited for the microscope -when about one inch long. The tadpoles of the newt and -toad also are equally suitable. They may be placed in a -very shallow glass trough with a little water, and a narrow -band of linen bound lightly round in some part not required -for examination, to keep them from moving; or they may -be laid upon a glass plate with a drop or two of water, and -a thin glass covering lightly bound upon it. Dr. Carpenter, -however, places them first in cold water, gradually adding -warm until the whole becomes about 100°, when the tadpole -becomes rigid, whilst the circulation is still maintained. I<span class="pagenum" id="Page_142">142</span> -have not, however, found this necessary, the thin glass -accomplishing all that is desired. The tail is generally the -most transparent, and shows the circulation best; but in -some of the newt larvæ the blood may be traced down to -the very extremities if they are not <em>too old</em>. Mr. Whitney -places the tadpole upon its back, by which means the heart -and other internal arrangements may be seen.</p> - -<p>Amongst fishes also may be found subjects for the -same purpose, but they seldom furnish as good examples as -those before mentioned, because the blood-vessels are not -nearly so abundant, as in the foot of the frog, &c. The -stickleback is, however, procurable almost in any place -during the summer months, and may be laid in a shallow -trough, loosely bound down as the tadpole. The tail may -be covered with a piece of thin glass to prevent him curling -it to the object-glass. The power needed with this will be -about the same as with the other subjects—viz., half to -quarter inch object-glass.</p> - -<p>It is not absolutely necessary to go to reptiles or fishes -for this curious sight, as some other animals serve very -well. In the wings of the common bat may be found a -good subject. These must be stretched out on something -resembling the frog-plate before described, when those parts -near to the bones will show the <em>largest</em> vessels very clearly. -The ear of a young mouse is an illustration of the same -phenomenon, but it is very difficult to fix it in a good -position, as these animals are so very timid and restless.</p> - -<p>Amongst insects also the same law may be observed, -by placing them in the “cage,” or “live-box,” so as to keep -them still, but not to injure them by too much pressure. In -certain larvæ this is particularly well shown, as that of the -day-fly and plumed gnat; but in some of these the blood is -almost colourless. In the wings also of many insects this -circulation is well seen, as in those of the common housefly; -but as these parts become dry in a few days, the -subject should not be more than twenty-four hours old.</p> - -<p>Somewhat approximating to the forementioned phenomenon,<span class="pagenum" id="Page_143">143</span> -is the “rotation” of fluid in the cells, or, as it is -usually termed, the <em>circulation of the sap</em>, of plants. This -is shown in certain vegetable growths as a constant stream -of thick fluid, wherein small globules are seen; which -stream flows round the individual cells, or up the leaf, turning -at the extremity, and down again by a different but -parallel channel. There is little or no difficulty in showing -this in many plants; but some are, of course, better than -others, and require a different treatment; we will, therefore, -notice a few of these. Perhaps the best of all is the -<i xml:lang="la" lang="la">Vallisneria spiralis</i>, which is an aquatic plant, frequently -grown in, but not really belonging to, this country. As it -somewhat resembles grass, the leaf is not used in its natural -state, but a thin section cut lengthwise with a razor or -other sharp instrument—this section, however, is much -better when the outer surface has been first removed. It -should then be laid upon a slide with a drop or two of -water, and covered with a piece of thin glass. Often the -cutting of the section seems to be such a shock to the leaf -that no motion is visible for awhile, but in a short time the -warmth of an ordinary sitting-room will revive it, and with -a quarter-inch object-glass the currents will be rendered -beautifully distinct. Where the “stream” is unusually -obstinate the warmth may be slightly increased, but too -great heat destroys the movement altogether. In the -summer, any of the leaves show this “circulation” very well; -but in the winter, the slightly yellow ones are said to be -the best.</p> - -<p>The Vallisneria requires to be cut in sections to show -this “circulation;” but there are many plants of which it -is but necessary to take a fragment and lay it upon a -slide. The <i xml:lang="la" lang="la">Anacharis alsinastrum</i> is one of these: it grows -in water, having three leaves round the stem, then a bare -portion, again another three leaves, and so on. One of -these leaves must be plucked close to the stem, and laid -upon a slide with a drop of water. Thin glass should be -placed upon it, and along the mid-rib of the leaves the<span class="pagenum" id="Page_144">144</span> -“circulation” may be seen most beautifully when a good -specimen has been chosen; but it requires rather more -power than the Vallisneria. This plant is very common -in many parts of the country, a great number of our -ponds and streams being literally choked up by it. In -the <i xml:lang="la" lang="la">Chara vulgaris</i> and two or three of the Nitellæ, &c., -this phenomenon may also be seen with no preparation -except plucking a part from the stem and laying it upon -a slide as with the Anacharis. In using the Frog-bit, the -outer part of the young leaf-buds must be taken to obtain -the best specimens for this purpose; but a section of the -stem will also show the “circulation,” though not so well. -The plants before mentioned are all aquatic, but the same -movement of the globules has been observed in several kinds -of land plants, as in the hairs upon the leaf-stalks of the -common groundsel; but these do not show it so well, nor -are they so easily managed as the above.</p> - -<p>Many microscopists who are not fortunate enough to be -in the neighbourhood of these plants (indeed the Vallisneria -is a foreign one) grow them in jars, so a few remarks as to -the treatment they require will not be out of place. The -Vallisneria requires a temperature not lower than 55° or -60°, and even a higher degree than this renders its growth -quicker; and no great change must take place: the more -equable the temperature the more healthy will the plant be. -A glass jar should be taken, having an inch or two of mould -at the bottom, which must be pressed down closely, and the -plant must be set in this. Water must then be gently -poured in, so as not to disturb the mould. As this plant -flourishes best when the water is frequently changed, -Mr. Quekett recommends that the jar should be occasionally -placed under a tap of water, and a very gentle stream -allowed to fall into it for several hours, by which means -much of the confervoid growth will be got rid of and the -plant invigorated. The Anacharis may be rooted in the -earth like the Vallisneria, but a small detached piece may -be thrown into the jar of water and there left until wanted.<span class="pagenum" id="Page_145">145</span> -For months the “circulation” will be well shown by -it, and it will probably grow and increase. It is also very -healthy in an in-door aquarium. It is recommended that -the jars in which any of the <i xml:lang="la" lang="la">Chara</i> are grown should be -moved about as little as possible, as the long roots are very -tender, and will not bear agitation.</p> - -<p>An object which is interesting to the microscopist, as -well as the unscientific observer, is the <em>growth</em> of seeds, as -it is often erroneously termed. A shaving of the outside -of the seed is taken and laid upon the glass slide; a thin -glass cover is then placed upon it, and a drop of water -applied to the edge of this. The water will then gradually -flow under the glass and reach the section of the seed, when -the transparent fibres will appear to spring out and “grow” -for some minutes. This, however, is produced by the unfolding -of a spiral formation in the cells, and, therefore, has -really no similarity to the true growth. The seeds of the -Salvias, Collomias, Senecio, Ruellia, &c., are well suited for -the display of this curious sight.</p> - -<p>To watch the development of the spores of ferns, and the -fertilization and products, Dr. Carpenter recommends the -following mode of proceeding:—“Let a frond of a fern, -whose fructification is mature, be laid upon a piece of fine -paper, with its spore-bearing surface downwards; in the -course of a day or two this paper will be found to be covered -with a very fine brownish dust, which consists of the discharged -spores. This must be carefully collected, and should -be spread upon the surface of a smoothed fragment of porous -sandstone; the stone being placed in a saucer, the bottom -of which is covered with water, and a glass ‘tumbler’ -being inverted over it, the requisite supply of moisture is -insured, and the spores will germinate luxuriantly. Some -of the prothallia soon advance beyond the rest; and at the -time when the advanced ones have long ceased to produce -antheridia, and bear abundance of archegonia, those which -have remained behind in their growth are beginning to be -covered with antheridia. If the crop be now kept with<span class="pagenum" id="Page_146">146</span> -little moisture for several weeks and then suddenly watered, -a large number of antheridia and archegonia simultaneously -open, and in a few hours afterwards the surface of the -larger prothallia will be found almost covered with moving -antherozoids. Such prothallia as exhibit freshly opened -archegonia are now to be held by one lobe between the -forefinger and thumb of the left hand, so that the upper -surface of the prothallium lies upon the thumb; and the -thinnest possible sections are then to be made with a -narrow-bladed knife perpendicularly to the surface of the -prothallium. Of these sections, which after much practice -may be made no more than 1-15th of a line of thickness, -some will probably lay open the canals of the archegonia, -and within these, when examined with a power of 200 or -300 diameters, antherozoids may be occasionally distinguished.”</p> - -<p>Another interesting object to the young microscopist is -afforded by the spores of the equiseta (or horsetails, as -they are often called). These may be obtained by shaking -the higher portion of the stems when the spores are ripe. -They will then fall like small dust, and may be placed -under the microscope. The spores are then seen to consist -of a somewhat heart-shaped mass with bands rather -intricately curled around it. As they dry these bands -expand, and are seen to be four lines at right angles, with -the ends clubbed, as it may be called. If, whilst watching -them, the spores are breathed upon, these bands immediately -return to their former state, and are closely curled around -the spore; but as they gradually dry again expand. This -experiment may be repeated many times, and is a very -interesting one.</p> - -<p>The above are the principal objects which could not possibly -be included in any of the former chapters, but would -have left a most interesting branch untouched had it -been neglected. There is another subject also which -should not be passed by—viz., the production of minute -pictures which serve as objects for microscopic examination.</p> - -<p>I may here mention that as this manual is<span class="pagenum" id="Page_147">147</span> -simply to enable the young student to prepare and mount -his objects, the photography of <em>magnified</em> objects has -evidently no place here.</p> - -<p>Few slides caused so much astonishment as these minute -photographs when first exhibited; small spots were seen to -contain large pictures, and a page of printed matter was -compressed into the one-hundredth part of a square inch. -It would be impossible in this place to give the inquirer -any instruction in the manipulation of photography, so it -must be assumed that he already knows this.</p> - -<p>We will first consider the process performed by artificial -light. The collodion employed in photographing generally -shows as much structure when magnified as is found in -linen of moderate texture; but this is not always the case, -as some samples bear much enlargement without any of -this appearance. It is evident that a structure so coarse -would make it entirely unfit for these minute pictures, as -all the small markings would be destroyed, or so interfered -with that no great enlargement would be practicable. -To obtain almost structureless collodion is not an easy -matter, and a clever practitioner in this branch of photography -states that he knows of no method to accomplish -this with certainty, but he himself tries different samples -until he falls upon a suitable one, which he then lays aside -for this object. A beneficial effect is often derived from -keeping the collodion awhile, but this is not always the -case. The slides should be chosen of an equal thickness, so -that when focussed upon one no re-adjustment may be -necessary for the others. The glass should, of course, be -free from any roughness, scratches, or other imperfections, -and of first-rate quality and colour.</p> - -<p>The microscope must then be placed in a horizontal -position, and the eye-piece removed, the stage having a -small clip upon it to keep the prepared plate in position. -The negative must then be supported at a distance from -the end of the microscope tube from which the eye-piece was<span class="pagenum" id="Page_148">148</span> -withdrawn. This distance will, of course, vary according to -the relative sizes of the negative and desired picture. -With a one-inch object-glass, which is a very convenient -focus, it will have to be changed usually betwixt one and -four feet. The negative must be lighted by an argand -gas-burner or camphine-lamp, and the rays rendered as -parallel as possible by the use of a large lens placed -betwixt the light and the negative. It is not easy to -arrange the apparatus so as to get the light <em>uniform</em>; but -a little practice will soon do away with this difficulty. -Ordinary ground-glass is too coarsely grained to focus upon, -as the magnifying power used to examine the minute -reflection must be considerable. One of the slides must -therefore be coated with the collodion, submitted to the -silver-bath, and after washing with water be allowed to -dry. Upon this may be focussed the reflected image, -and its minuteness examined with a powerful hand-magnifier, -or another microscope placed behind in a horizontal -position. When the utmost sharpness of definition is -obtained, it is usually required to remove the plate a little -distance from the object-glass, as object-glasses for the -microscope are slightly “over corrected,” and the chemical -rays which accomplish the photography are beyond the -visual ones. The exact distance required to give a picture -to bear the greatest enlargement cannot be given by rule; -but experiments must be made at first, and it will always -be the same with the object-glass which we have tested.</p> - -<p>The plate may now be prepared as in ordinary photography, -and placed upon the stage whilst the light is -shaded. When all is ready, the shade is removed and the -process allowed to go on, usually for thirty or forty seconds; -but no certain rule can be given as to the required time, on -account of various collodions, lamps, and powers being used. -It may be here mentioned, that it is well to contrive some -little frame to receive the prepared plate, as the silver bath -solution is liable to get upon the microscope stage and so, -to say the least, disfigure it. When the exposure has been<span class="pagenum" id="Page_149">149</span> -continued sufficiently long, the picture may be developed by -any of the ordinary methods, but some of the best productions -have been brought out by the aid of pyrogallic and -citric acid solution, with the addition of a little alcohol. -The “fixing” may be effected by a strong solution of hypo-sulphite -of soda, and the picture must then be very well -washed with pure water. When dry, the photograph must -be mounted with Canada balsam, in the same manner as -any ordinary object; but great heat must not be used, or -the picture may be injured.</p> - -<p>When ordinary daylight is employed for this purpose, -a dark slide will be required for the prepared plate, -in the same way as for photographing landscape, &c. -These dark slides are generally made by each individual -to suit his particular arrangements of negatives, &c.; but -it may be here recommended that the operator should -always focus in the same slide which he is about to use, as -so small a difference in distance lies betwixt perfection and -failure.</p> - -<p>For an ordinary student, perhaps the above method is that -which is the most readily used, and consequently the most -generally available; but almost every one has a different -arrangement of microscope, &c., by which he procures these -minute pictures. Mr. Shadbolt (one of our most successful -photographers) gives the following instructions:—“Having -removed the upper stage plate of a large compound microscope, -I replace it with one of wood, supplied with guide -pins of silver wire, in order to admit of its supporting a slip -of glass coated with collodion, and excited in the nitrate -of silver bath in the usual way. If the ordinary brass -stage plate were left undisturbed, it is obvious that it and -the excited slip of glass would be mutually destructive.</p> - -<p>“The microscope is now to be placed in a horizontal -position, the objective, intended to produce the picture, -made to occupy the place usually filled by the achromatic -condenser on the <em>sub-stage</em> of the microscope, while <em>another</em> -objective is screwed into the lower end of the body of the<span class="pagenum" id="Page_150">150</span> -instrument, which is used not only to focus with, but also -to make the requisite allowance for actinic variation.</p> - -<p>“The negative intended to be reduced is then arranged -vertically, with its centre in the axis of the microscopic -body, at a distance of from two to four feet from the lower -object-glass, and with a convenient screen of card, wood, or -thick paper, to cut off any extraneous light that would -otherwise pass beyond the limits of the picture.</p> - -<p>“A small camphine-lamp is employed for the purpose of -illuminating the negative, having a good bull’s-eye lens as -a condenser, so arranged with its flat side next the lamp -that the refracted rays shall just fill the whole of a double -convex lens of about six inches in diameter, the latter being -placed in such a position as to refract the rays of light in a -parallel direction upon the negative. By this arrangement -the <em>bull’s-eye lens</em> of about two inches and a half in -diameter <em>appears</em> as the source of the light instead of the -small flame of the lamp.</p> - -<p>“By using a bat’s-wing gas-burner of a good size, a <em>single</em> -lens, instead of the two, may be so placed as to give the -necessary uniformity of illumination.”</p> - -<p>This arrangement requires the same care in working as -that before mentioned, the pictures being produced, developed, -and fixed by the same treatment.</p> - -<p>As before stated, almost every manipulator makes -some small changes in the method of producing these -minute pictures; but the rules given, though far from -new, are sufficient for all purposes; and I may state with -truth, that those which I procured when these wonders -were quite new, are fully equal in every respect to the best -usually met with at the present time.</p> - -<p>With these instructions I shall close my Handbook, as I -believe that every branch of Preparation and Mounting -of Microscopic Objects has been treated of. Not that -the beginner can expect that he has nothing to do except -read this to be able to mount everything; but there -are difficulties from which he may be freed by instruction,<span class="pagenum" id="Page_151">151</span> -when otherwise he would have been compelled to learn by -failure alone. I may, here, however, repeat certain advice -before given,—that, when practicable, it is a good thing -to mount each object by two or more different methods, -as very frequently one feature is best shown dry, another in -liquid, and a third in balsam. Secondly, let the <em>mounting</em> -be studied thoroughly, as no part of the microscopic -science is more worthy of thought than this. And lastly, -let no failures prevent you following up what will assuredly -one day become a source of great pleasure, and render your -daily “constitutional walk,” which is often dull in the -extreme, very delightful, as it will afford you some new -wonder in every hedge-row.</p> - -<hr /> - -<p><span class="pagenum" id="Page_153">153</span></p> - -<div class="chapter"><div class="index"> -<h2 id="INDEX" class="nobreak p1">INDEX.</h2> - -<ul class="index nobreak"> -<li class="ifrst">Air-bubbles, <a href="#Page_56">56</a>.</li> - -<li class="indx">Air-pump, <a href="#Page_13">13</a>;</li> -<li class="isub1">use of, <a href="#Page_57">57</a>.</li> - -<li class="indx">Alcock, Dr., on tongues of Mollusca, <a href="#Page_118">118</a>.</li> - -<li class="indx">Algæ, mounting of, <a href="#Page_91">91</a>.</li> - -<li class="indx">Anacharis alsinastrum, rotation in, <a href="#Page_143">143</a>;</li> -<li class="isub1">to cultivate, <a href="#Page_144">144</a>.</li> - -<li class="indx">Animal tissues, dissection of, <a href="#Page_114">114</a>.</li> - -<li class="indx">Antennæ of insects, <a href="#Page_71">71</a>;</li> -<li class="isub1">in preservative liquid, <a href="#Page_94">94</a>.</li> - -<li class="indx">Apparatus required in mounting objects, <a href="#CHAPTER_I">i.</a></li> - -<li class="indx">Arteries, how to distinguish, in injection, <a href="#Page_131">131</a>.</li> - -<li class="indx">Asparagus, spiral vessels of, <a href="#Page_114">114</a>.</li> - -<li class="indx">Asphaltum, <a href="#Page_15">15</a>;</li> -<li class="isub1">and india-rubber, as cement and varnish, <a href="#Page_18">18</a>.</li> - -<li class="ifrst">Bat, circulation of blood in wings of, <a href="#Page_142">142</a>.</li> - -<li class="indx">Beale’s, Dr., Prussian blue for injecting, <a href="#Page_134">134</a>;</li> -<li class="isub1">carmine, <a href="#Page_135">135</a>.</li> - -<li class="indx">Bell-glasses, use of, <a href="#Page_12">12</a>.</li> - -<li class="indx">Berg-mehl, <a href="#Page_40">40</a>.</li> - -<li class="indx">Bermuda earth, <a href="#Page_40">40</a>.</li> - -<li class="indx">Bichromate of lead, injection with, <a href="#Page_132">132</a>.</li> - -<li class="indx">Bird, Dr. Golding, on preparation of Zoophytes, <a href="#Page_65">65</a>.</li> - -<li class="indx">Black-japan, as a cement, <a href="#Page_16">16</a>.</li> - -<li class="indx">Black varnish, <a href="#Page_18">18</a>.</li> - -<li class="indx">Blood, as a microscopic object, <a href="#Page_50">50</a>;</li> -<li class="isub1">circulation of, <a href="#Page_140">140–142</a>.</li> - -<li class="indx">Bone, sections of, <a href="#Page_102">102</a>;</li> -<li class="isub1">fossil, <a href="#Page_103">103</a>.</li> - -<li class="indx">Brass plate for heating glasses, &c., <a href="#Page_13">13</a>.</li> - -<li class="ifrst">Cactaceæ, raphides of, <a href="#Page_52">52</a>.</li> - -<li class="indx">Camel-hair pencils, use of, <a href="#Page_10">10</a>.</li> - -<li class="indx"><a id="Canada_balsam"></a>Canada balsam, <a href="#Page_14">14</a>;</li> -<li class="isub1">with chloroform, <a href="#Page_14">14</a>, <a href="#Page_60">60</a>, <a href="#Page_132">132</a>;</li> -<li class="isub1">with turpentine, <a href="#Page_14">14</a>;</li> -<li class="isub1">air bubbles in, <a href="#Page_56">56</a>;</li> -<li class="isub1">Dr. Carpenter’s syringe for, <a href="#Page_59">59</a>;</li> -<li class="isub1">to fill cells with, <a href="#Page_60">60</a>;</li> -<li class="isub1">mounting of objects in, <a href="#Page_56">56</a>.</li> - -<li class="indx">Carbolic acid, <a href="#Page_86">86</a>.</li> - -<li class="indx">Carmine injecting fluid, Dr. Beale’s, 135:</li> -<li class="isub1">Dale & Davies’, <a href="#Page_138">138</a>.</li> - -<li class="indx">Cartilage, dissection of, <a href="#Page_114">114</a>.</li> - -<li class="indx">Castor oil, as a preservative, <a href="#Page_86">86</a>.</li> - -<li class="indx">Cells for dry objects, <a href="#Page_6">6</a>;</li> -<li class="isub1">with rings of cardboard, <a href="#Page_7">7</a>;</li> -<li class="isub1">with gutta-percha, <a href="#Page_7">7</a>;</li> -<li class="isub1">with leather, <a href="#Page_7">7</a>;</li> -<li class="isub1">with ivory, <a href="#Page_8">8</a>;</li> -<li class="isub1">with thin glass, <a href="#Page_7">7</a>;</li> -<li class="isub1">with varnish, <a href="#Page_23">23</a>, <a href="#Page_26">26</a>;</li> -<li class="isub1">for balsam, <a href="#Page_60">60</a>;</li> -<li class="isub1">for preservative liquids, <a href="#Page_87">87–89</a>;</li> -<li class="isub1">Shadbolt’s turntable useful in making, <a href="#Page_9">9</a>.</li> - -<li class="indx">Cements, <a href="#Page_13">13–17</a>.</li> - -<li class="indx">Chalk, foraminifera from, <a href="#Page_63">63</a>.</li> - -<li class="indx">Chara vulgaris, rotation in, <a href="#Page_144">144</a>.</li> - -<li class="indx">Chloride of zinc, solution of, <a href="#Page_85">85</a>;</li> -<li class="isub1">of calcium, solution of, <a href="#Page_92">92</a>.</li> - -<li class="indx">Chloroform, use of (<i>see</i> <a href="#Canada_balsam">Canada balsam</a>).</li> - -<li class="indx">Circulation of blood, <a href="#Page_140">140–142</a>;</li> -<li class="isub1">of sap (<i>see</i> <a href="#Rotation_of_fluid_in_cells_of_plants">Rotation</a>).</li> - -<li class="indx">Cleanliness in microscopic work, <a href="#Page_1">1</a>.<span class="pagenum" id="Page_154">154</span></li> - -<li class="indx">Coal, sections of, <a href="#Page_99">99</a>.</li> - -<li class="indx">Collection of diatoms, <a href="#Page_29">29</a>.</li> - -<li class="indx">Colours for injection, <a href="#Page_125">125–127</a>.</li> - -<li class="indx">Condenser, cheap, to make, <a href="#Page_20">20</a>.</li> - -<li class="indx">Corals, sections of, <a href="#Page_99">99</a>.</li> - -<li class="indx">Corallines, to mount, <a href="#Page_48">48</a>.</li> - -<li class="indx">Cover of objects, to remove, <a href="#Page_60">60</a>.</li> - -<li class="indx">Crystals, mounting of, dry, <a href="#Page_50">50</a>;</li> -<li class="isub1">to vary form of, and mount in balsam, <a href="#Page_75">75</a>;</li> -<li class="isub1">sections of, <a href="#Page_109">109</a>.</li> - -<li class="indx">Cuticle of equisetum, &c., <a href="#Page_80">80</a>.</li> - -<li class="ifrst">Dale & Davies’, carmine injection, <a href="#Page_138">138</a>.</li> - -<li class="indx">Deane’s gelatine, <a href="#Page_84">84</a>.</li> - -<li class="indx">Decalcifying process for shells, <a href="#Page_98">98</a>.</li> - -<li class="indx">Desmidiaceæ, in preservative liquid, <a href="#Page_92">92</a>.</li> - -<li class="indx">Diachæa elegans, <a href="#Page_53">53</a>.</li> - -<li class="indx">Diamond beetle, <a href="#Page_54">54</a>.</li> - -<li class="indx">Diatomaceæ, nature of, <a href="#Page_28">28</a>;</li> -<li class="isub1">collection of, <a href="#Page_29">29</a>;</li> -<li class="isub1">in stomachs of fish, <a href="#Page_30">30</a>;</li> -<li class="isub1">to prepare and mount dry, <a href="#Page_30">30–40</a>;</li> -<li class="isub1">Mr. Rylands on, <a href="#Page_33">33</a>;</li> -<li class="isub1">in guano, <a href="#Page_39">39</a>;</li> -<li class="isub1">fossilized, <a href="#Page_40">40</a>;</li> -<li class="isub1">mounting in balsam, <a href="#Page_61">61</a>;</li> -<li class="isub1">mounting in preservative liquids, <a href="#Page_92">92</a>, <a href="#Page_93">93</a>.</li> - -<li class="indx">Discs used in mounting, <a href="#Page_22">22</a>;</li> -<li class="isub1">supporter, Smith & Beck’s, <a href="#Page_23">23</a>.</li> - -<li class="indx"><a id="Dissection"></a>Dissection, <a href="#Page_111">111</a>;</li> -<li class="isub1">microscope for, <a href="#Page_111">111</a>;</li> -<li class="isub1">instruments for, <a href="#Page_112">112</a>.</li> - -<li class="indx">Distilled water, as preservative liquid, <a href="#Page_83">83</a>.</li> - -<li class="indx">Doyer’s, M., method of injection, <a href="#Page_132">132</a>.</li> - -<li class="indx">Dry objects, to mount, <a href="#Page_22">22</a>.</li> - -<li class="ifrst">Echinodermata spines, sections of, <a href="#Page_99">99</a>.</li> - -<li class="indx">Eel, scales of, <a href="#Page_78">78</a>.</li> - -<li class="indx">Eggs of insects, <a href="#Page_94">94</a>.</li> - -<li class="indx">Elastic objects, to keep flat upon the slide, <a href="#Page_11">11</a>.</li> - -<li class="indx">Electrical cement, <a href="#Page_16">16</a>.</li> - -<li class="indx">Equisetaceæ, <a href="#Page_80">80</a>;</li> -<li class="isub1">spores of, <a href="#Page_146">146</a>.</li> - -<li class="indx">Erector, not indispensable, <a href="#Page_19">19</a>.</li> - -<li class="indx">Eyes of insects, <a href="#Page_70">70</a>, <a href="#Page_54">54</a>;</li> -<li class="isub1">of animals injected, <a href="#Page_136">136</a>.</li> - -<li class="ifrst">Feathers, <a href="#Page_73">73</a>.</li> - -<li class="indx">Feet of insects, <a href="#Page_54">54</a>, <a href="#Page_71">71</a>.</li> - -<li class="indx">Ferns, <a href="#Page_51">51</a>;</li> -<li class="isub1">development of spores of, <a href="#Page_145">145</a>.</li> - -<li class="indx">Fish, fins and tails of, <a href="#Page_50">50</a>;</li> -<li class="isub1">scales of, <a href="#Page_53">53</a>, <a href="#Page_78">78</a>;</li> -<li class="isub1">injection of, <a href="#Page_137">137</a>;</li> -<li class="isub1">circulation of blood in, <a href="#Page_142">142</a>.</li> - -<li class="indx">Flint, sections of, <a href="#Page_101">101</a>.</li> - -<li class="indx">Fluid, mounting objects in, <a href="#Page_83">83</a>.</li> - -<li class="indx">Flustra avicularis, <a href="#Page_79">79</a>.</li> - -<li class="indx">Fly (<i>see</i> <a href="#Insects">Insects</a>).</li> - -<li class="indx">Foot of sheep injected, <a href="#Page_136">136</a>.</li> - -<li class="indx">Foraminifera, <a href="#Page_41">41</a>;</li> -<li class="isub1">separation of, <a href="#Page_41">41</a>;</li> -<li class="isub1">to clean, <a href="#Page_42">42</a>;</li> -<li class="isub1">to clean from tallow soundings, <a href="#Page_42">42</a>;</li> -<li class="isub1">to mount, <a href="#Page_45">45</a>, <a href="#Page_63">63</a>;</li> -<li class="isub1">from chalk, <a href="#Page_63">63</a>.</li> - -<li class="indx">Forceps, ordinary and wooden, <a href="#Page_11">11</a>;</li> -<li class="isub1">bull-nosed, for injection, <a href="#Page_123">123</a>.</li> - -<li class="indx">Fossil infusoria, <a href="#Page_40">40</a>.</li> - -<li class="indx">Frog, injected, <a href="#Page_136">136</a>;</li> -<li class="isub1">to show circulation of blood, <a href="#Page_140">140</a>.</li> - -<li class="indx">Frog-bit, rotation in, <a href="#Page_144">144</a>.</li> - -<li class="indx">Fruit-stones, sections of, <a href="#Page_104">104</a>.</li> - -<li class="indx"><a id="Fungi"></a>Fungi, <a href="#Page_53">53</a>, <a href="#Page_94">94</a>.</li> - -<li class="ifrst">Gastric teeth of insects, <a href="#Page_120">120</a>;</li> -<li class="isub1">of molluscs, <a href="#Page_117">117</a>.</li> - -<li class="indx">Gelatine for injection, <a href="#Page_124">124</a>;</li> -<li class="isub1">preservative liquid, <a href="#Page_84">84</a>.</li> - -<li class="indx">Glass slides, <a href="#Page_1">1</a>;</li> -<li class="isub1">thin, <a href="#Page_3">3</a>;</li> -<li class="isub1">thin, to cut, <a href="#Page_3">3</a>;</li> -<li class="isub1">thin, to measure, <a href="#Page_4">4</a>;</li> -<li class="isub1">thin, to clean, <a href="#Page_5">5</a>;</li> -<li class="isub1">cells, to make, <a href="#Page_88">88</a>;</li> -<li class="isub1">rings for cells, <a href="#Page_88">88</a>;</li> -<li class="isub1">tubes, <a href="#Page_10">10</a>.</li> - -<li class="indx">Glycerine, <a href="#Page_84">84</a>, <a href="#Page_94">94</a>;</li> -<li class="isub1">jelly, <a href="#Page_84">84</a>, <a href="#Page_91">91</a>.</li> - -<li class="indx">Goadby’s fluid, <a href="#Page_85">85</a>.</li> - -<li class="indx">Gold-size, <a href="#Page_15">15</a>.</li> - -<li class="indx">Grasses, <a href="#Page_80">80</a>.</li> - -<li class="indx">Grasshopper, gizzard of, <a href="#Page_120">120</a>.<span class="pagenum" id="Page_155">155</span></li> - -<li class="indx">Guano, containing Diatomaceæ, <a href="#Page_39">39</a>.</li> - -<li class="indx">Gum-water, and modifications of, <a href="#Page_17">17</a>.</li> - -<li class="indx">Gutta-percha cells, <a href="#Page_7">7</a>;</li> -<li class="isub1">for liquids, <a href="#Page_87">87</a>.</li> - -<li class="ifrst">Hairs, vegetable, <a href="#Page_46">46</a>;</li> -<li class="isub1">to mount dry, <a href="#Page_54">54</a>;</li> -<li class="isub1">to mount as polarizing objects, <a href="#Page_79">79</a>;</li> -<li class="isub1">sections of, <a href="#Page_105">105</a>.</li> - -<li class="indx">Hepworth, Mr., on mounting insects, <a href="#Page_68">68</a>.</li> - -<li class="indx">Horn, sections of, <a href="#Page_104">104</a>.</li> - -<li class="indx">Hot-water bath, use of, <a href="#Page_58">58</a>.</li> - -<li class="ifrst">Infusoria, in preservative liquid, <a href="#Page_92">92</a>;</li> -<li class="isub1">fossil, <a href="#Page_40">40</a>.</li> - -<li class="indx">Injections, <a href="#CHAPTER_VI">vi.</a>, <a href="#Page_122">122</a>;</li> -<li class="isub1">apparatus for, <a href="#Page_122">122</a>;</li> -<li class="isub1">colours for, <a href="#Page_125">125</a>;</li> -<li class="isub1">directions for, <a href="#Page_127">127</a>;</li> -<li class="isub1">with various colours, <a href="#Page_131">131</a>;</li> -<li class="isub1">mounting of, <a href="#Page_131">131</a>;</li> -<li class="isub1">transparent, <a href="#Page_133">133</a>, <a href="#Page_138">138</a>.</li> - -<li class="indx"><a id="Insects"></a>Insects, scales of, <a href="#Page_48">48</a>;</li> -<li class="isub1">to mount, <a href="#Page_49">49</a>;</li> -<li class="isub1">legs and feet of, <a href="#Page_54">54</a>, <a href="#Page_72">72</a>;</li> -<li class="isub1">eyes of, <a href="#Page_54">54</a>, <a href="#Page_70">70</a>;</li> -<li class="isub1">Mr. Hepworth on mounting, <a href="#Page_68">68</a>;</li> -<li class="isub1">antennæ of, <a href="#Page_71">71</a>;</li> -<li class="isub1">mouth of, <a href="#Page_72">72</a>;</li> -<li class="isub1">tracheæ and spiracles of, <a href="#Page_72">72</a>, <a href="#Page_115">115</a>;</li> -<li class="isub1">parasitic, <a href="#Page_73">73</a>;</li> -<li class="isub1">in preservative liquid, <a href="#Page_94">94</a>;</li> -<li class="isub1">eggs of, <a href="#Page_94">94</a>;</li> -<li class="isub1">gizzard of, <a href="#Page_120">120</a>;</li> -<li class="isub1">circulation of blood in, <a href="#Page_142">142</a>.</li> - -<li class="indx">Intestines, injected, <a href="#Page_136">136</a>.</li> - -<li class="ifrst">Knives for dissecting, <a href="#Page_112">112</a>;</li> -<li class="isub1">Valentin’s, <a href="#Page_108">108</a>.</li> - -<li class="ifrst">Labelling of objects, <a href="#Page_19">19</a>.</li> - -<li class="indx">Lamps, for mounting, <a href="#Page_12">12</a>.</li> - -<li class="indx">Larvæ, skins of, <a href="#Page_50">50</a>.</li> - -<li class="indx">Leaves, sections of, <a href="#Page_107">107</a>;</li> -<li class="isub1">scales of, <a href="#Page_46">46</a>, <a href="#Page_81">81</a>.</li> - -<li class="indx">Liquid-glue, <a href="#Page_16">16</a>.</li> - -<li class="indx">Lungs of animals injected, <a href="#Page_137">137</a>.</li> - -<li class="ifrst">Mallow, pollen of, <a href="#Page_47">47</a>.</li> - -<li class="indx">Marine glue, <a href="#Page_15">15</a>, <a href="#Page_88">88</a>.</li> - -<li class="indx">Microscope for dissection, <a href="#Page_111">111</a>.</li> - -<li class="indx">Miscellaneous, <a href="#CHAPTER_VII">vii.</a>, <a href="#Page_140">140</a>.</li> - -<li class="indx">Mites, <a href="#Page_73">73</a>.</li> - -<li class="indx">Molluscs, tongues of, <a href="#Page_116">116</a>.</li> - -<li class="indx">Mosses, <a href="#Page_51">51</a>;</li> -<li class="isub1">in preservative fluids, <a href="#Page_91">91</a>.</li> - -<li class="indx">Mould (<i>see</i> <a href="#Fungi">Fungi</a>).</li> - -<li class="indx">Mounting objects, apparatus for, <a href="#CHAPTER_I">i.</a>;</li> -<li class="isub1">dry, <a href="#CHAPTER_II">ii.</a>, <a href="#Page_22">22</a>;</li> -<li class="isub1">in Canada balsam, <a href="#CHAPTER_III">iii.</a>, <a href="#Page_56">56</a>;</li> -<li class="isub1">in cells, <a href="#CHAPTER_IV">iv.</a>, <a href="#Page_83">83</a>.</li> - -<li class="indx">Mouse, ear of, <a href="#Page_114">114</a>;</li> -<li class="isub1">circulation of blood in, <a href="#Page_142">142</a>.</li> - -<li class="indx">Mouth of insects, <a href="#Page_72">72</a>.</li> - -<li class="indx">Muscle, dissection of, <a href="#Page_114">114</a>.</li> - -<li class="ifrst">Needles, how to mount, <a href="#Page_10">10</a>;</li> -<li class="isub1">for dissection, <a href="#Page_112">112</a>;</li> -<li class="isub1">curved, for injection, <a href="#Page_123">123</a>.</li> - -<li class="indx">Nervous tissue, dissection of, <a href="#Page_115">115</a>.</li> - -<li class="indx">Nettle leaf, <a href="#Page_52">52</a>.</li> - -<li class="indx">Newts, injected, <a href="#Page_136">136</a>.</li> - -<li class="ifrst">Onion, raphides of, <a href="#Page_52">52</a>.</li> - -<li class="indx">Orbitolite, section of, <a href="#Page_97">97</a>.</li> - -<li class="indx">Oxalurate of ammonia, crystals of, <a href="#Page_75">75</a>.</li> - -<li class="ifrst">Palates of Molluscs (<i>see</i> <a href="#Tongues">tongues</a>).</li> - -<li class="indx">Papers, ornamental, to cover slides, <a href="#Page_8">8</a>, <a href="#Page_27">27</a>.</li> - -<li class="indx">Photographs, microscopic, to produce, <a href="#Page_147">147</a>;</li> -<li class="isub1">Mr. Shadbolt on, <a href="#Page_149">149</a>.</li> - -<li class="indx">Pipes for injecting syringe, <a href="#Page_122">122</a>.</li> - -<li class="indx">Podura, scales of, <a href="#Page_49">49</a>.</li> - -<li class="indx">Polariscope, objects for, <a href="#Page_74">74–82</a>, <a href="#Page_104">104</a>.</li> - -<li class="indx">Pollen, <a href="#Page_47">47</a>, <a href="#Page_74">74</a>.</li> - -<li class="indx">Polycystina, preparation and mounting of, <a href="#Page_63">63</a>.</li> - -<li class="indx">Preservative liquids, <a href="#CHAPTER_IV">iv.</a>, <a href="#Page_83">83</a>;</li> -<li class="isub1">cells suited for, <a href="#Page_87">87–89</a>.</li> - -<li class="indx">Prussian blue for injection, <a href="#Page_134">134</a>.</li> - -<li class="ifrst">Raphides, vegetable, <a href="#Page_52">52</a>, <a href="#Page_80">80</a>.</li> - -<li class="indx">Rhinoceros, horn of, <a href="#Page_104">104</a>.</li> - -<li class="indx">Rhubarb, spiral vessels of, <a href="#Page_113">113</a>.</li> - -<li class="indx">Rings and cross of crystals, <a href="#Page_109">109</a>.</li> - -<li class="indx"><a id="Rotation_of_fluid_in_cells_of_plants"></a>Rotation of fluid in cells of plants, <a href="#Page_143">143–145</a>.</li> - -<li class="indx">Rush, section of, <a href="#Page_108">108</a>.<span class="pagenum" id="Page_156">156</span></li> - -<li class="indx">Rylands, Mr. T. G., on Diatomaceæ, <a href="#Page_33">33</a>, <a href="#Page_93">93</a>.</li> - -<li class="ifrst">Salicine, crystals of, <a href="#Page_76">76</a>.</li> - -<li class="indx">Saw of watch-spring, <a href="#Page_97">97</a>.</li> - -<li class="indx">Scales of fishes, <a href="#Page_53">53</a>, <a href="#Page_78">78</a>;</li> -<li class="isub1">of leaves, <a href="#Page_46">46</a>, <a href="#Page_81">81</a>;</li> -<li class="isub1">of insects, <a href="#Page_48">48</a>.</li> - -<li class="indx">Scissors, <a href="#Page_10">10</a>;</li> -<li class="isub1">for dissection, <a href="#Page_112">112</a>.</li> - -<li class="indx">Sea-mats, <a href="#Page_53">53</a>.</li> - -<li class="indx">Sea-soundings, to cleanse, <a href="#Page_42">42</a>.</li> - -<li class="indx">Sealing-wax varnish, <a href="#Page_17">17</a>.</li> - -<li class="indx">Sections, <a href="#Page_96">96</a>;</li> -<li class="isub1">of shells, <a href="#Page_97">97</a>;</li> -<li class="isub1">of orbitolite, <a href="#Page_97">97</a>;</li> -<li class="isub1">of spines of Echinodermata, <a href="#Page_99">99</a>;</li> -<li class="isub1">of corals, <a href="#Page_99">99</a>;</li> -<li class="isub1">of coal, <a href="#Page_99">99</a>;</li> -<li class="isub1">of flint, <a href="#Page_101">101</a>;</li> -<li class="isub1">of teeth, <a href="#Page_101">101</a>;</li> -<li class="isub1">of bone, <a href="#Page_102">102</a>;</li> -<li class="isub1">of fruit-stones, <a href="#Page_104">104</a>;</li> -<li class="isub1">of horn, <a href="#Page_104">104</a>;</li> -<li class="isub1">of whalebone, <a href="#Page_105">105</a>;</li> -<li class="isub1">of hairs, <a href="#Page_105">105</a>;</li> -<li class="isub1">of wood, <a href="#Page_106">106</a>;</li> -<li class="isub1">of leaves, <a href="#Page_107">107</a>;</li> -<li class="isub1">of sponges, <a href="#Page_108">108</a>;</li> -<li class="isub1">of skin, <a href="#Page_109">109</a>;</li> -<li class="isub1">of crystals, <a href="#Page_109">109</a>;</li> -<li class="isub1">of seeds, <a href="#Page_111">111</a>.</li> - -<li class="indx">Seeds, <a href="#Page_47">47</a>, <a href="#Page_74">74</a>;</li> -<li class="isub1">sections of, <a href="#Page_111">111</a>;</li> -<li class="isub1">growth of, <a href="#Page_145">145</a>.</li> - -<li class="indx">Shadbolt’s turntable, <a href="#Page_9">9</a>.</li> - -<li class="indx">Shells, sections of, <a href="#Page_97">97</a>;</li> -<li class="isub1">decalcifying, <a href="#Page_98">98</a>;</li> -<li class="isub1">laminæ of, <a href="#Page_98">98</a>.</li> - -<li class="indx">Siliceous cuticles, <a href="#Page_80">80</a>.</li> - -<li class="indx">Size for injection, <a href="#Page_124">124</a>.</li> - -<li class="indx">Skins of larvæ, <a href="#Page_50">50</a>;</li> -<li class="isub1">sections of, <a href="#Page_109">109</a>;</li> -<li class="isub1">sole, <a href="#Page_54">54</a>.</li> - -<li class="indx">Slides, glass, for mounting objects, <a href="#Page_1">1</a>;</li> -<li class="isub1">glass, to clean, <a href="#Page_2">2</a>;</li> -<li class="isub1">wood, &c., <a href="#Page_6">6</a>;</li> -<li class="isub1">most useful, <a href="#Page_8">8</a>;</li> -<li class="isub1">to cover and varnish, <a href="#Page_27">27</a>.</li> - -<li class="indx">Spicula, from sponges, &c., <a href="#Page_67">67</a>.</li> - -<li class="indx">Spines of Echinus, <a href="#Page_99">99</a>.</li> - -<li class="indx">Spiracles of insects, <a href="#Page_72">72</a>, <a href="#Page_116">116</a>.</li> - -<li class="indx">Spiral vessels of vegetables, <a href="#Page_113">113</a>.</li> - -<li class="indx">Split bristles, use of, <a href="#Page_10">10</a>.</li> - -<li class="indx">Sponges, sections of, <a href="#Page_108">108</a>.</li> - -<li class="indx">Spores of ferns, development of, <a href="#Page_145">145</a>;</li> -<li class="isub1">equisetum, <a href="#Page_146">146</a>.</li> - -<li class="indx">Starch, preparation and mounting of, <a href="#Page_79">79</a>.</li> - -<li class="indx">Sulphate of copper and magnesia, crystals of, <a href="#Page_76">76</a>.</li> - -<li class="indx">Syringe for Canada balsam, <a href="#Page_59">59</a>;</li> -<li class="isub1">for dissection, <a href="#Page_113">113</a>;</li> -<li class="isub1">for injection, <a href="#Page_122">122</a>.</li> - -<li class="ifrst">Tadpole, to show circulation of blood of, <a href="#Page_141">141</a>.</li> - -<li class="indx">Teeth, sections of, <a href="#Page_101">101</a>.</li> - -<li class="indx">Thin glass, to cut, <a href="#Page_3">3</a>;</li> -<li class="isub1">to measure thickness of, <a href="#Page_4">4</a>;</li> -<li class="isub1">to clean, <a href="#Page_5">5</a>.</li> - -<li class="indx">Thwaites’ preservative liquid, <a href="#Page_85">85</a>.</li> - -<li class="indx">Ticks, <a href="#Page_73">73</a>.</li> - -<li class="indx">Tissues, animal and vegetable (<i>see</i> <a href="#Dissection">Dissection</a>).</li> - -<li class="indx"><a id="Tongues"></a>Tongues or palates of Molluscs, <a href="#Page_116">116</a>.</li> - -<li class="indx">Tracheæ of insects, <a href="#Page_72">72</a>, <a href="#Page_115">115</a>.</li> - -<li class="indx">Transfer of objects, <a href="#Page_10">10</a>.</li> - -<li class="indx">Trough for dissection, <a href="#Page_113">113</a>.</li> - -<li class="indx">Tubes, glass, <a href="#Page_10">10</a>.</li> - -<li class="indx">Turnbull’s, Dr., Prussian blue for injection, <a href="#Page_134">134</a>.</li> - -<li class="indx">Turpentine, use of, <a href="#Page_57">57</a>.</li> - -<li class="ifrst">Universal stand, to make, <a href="#Page_20">20</a>.</li> - -<li class="ifrst">Valentin’s knife, <a href="#Page_108">108</a>.</li> - -<li class="indx">Vallisneria spiralis, rotation in, <a href="#Page_143">143</a>;</li> -<li class="isub1">to cultivate, <a href="#Page_144">144</a>.</li> - -<li class="indx">Varnishes, <a href="#Page_17">17</a>.</li> - -<li class="indx">Vegetable objects, to mount dry, <a href="#Page_46">46</a>;</li> -<li class="isub1">to mount in jelly, <a href="#Page_91">91</a>;</li> -<li class="isub1">dissection of, <a href="#Page_113">113</a>.</li> - -<li class="ifrst">Watch-glasses, <a href="#Page_12">12</a>.</li> - -<li class="indx">Whalebone, sections of, <a href="#Page_105">105</a>.</li> - -<li class="indx">Wood, sections of, <a href="#Page_106">106</a>.</li> - -<li class="ifrst">Zoophytes, to mount dry, <a href="#Page_53">53</a>;</li> -<li class="isub1">Dr. Golding Bird on mounting, in balsam, <a href="#Page_65">65</a>;</li> -<li class="isub1">as polarizing objects, <a href="#Page_79">79</a>.</li> -</ul> -</div></div> - -<p class="p2 center"><span class="small wspace bt">COX AND WYMAN, PRINTERS, GREAT QUEEN STREET, LONDON.</span></p> - -<div class="chapter"><div class="transnote"> -<h2 id="Transcribers_Notes" class="nobreak p1">Transcriber’s Notes</h2> - -<p>Punctuation and spelling were made consistent when a predominant -preference was found in the original book; otherwise they were not -changed.</p> - -<p>Inconsistent hyphenation was not changed.</p> - -<p>Simple typographical errors were corrected; unbalanced quotation -marks were remedied when the change was obvious, and otherwise left -unbalanced.</p> - -<p>The Table of Contents was added by the Transcriber.</p> - -<p>The index was not checked for proper alphabetization or correct page -references. Roman numeral references are to chapters, not to pages.</p> -</div></div> - - - - - - - - -<pre> - - - - - -End of the Project Gutenberg EBook of The Preparation & Mounting of -Microscopic Objects, by Thomas Davies - -*** END OF THIS PROJECT GUTENBERG EBOOK PREPARATION OF MICROSCOPIC OBJECTS *** - -***** This file should be named 60225-h.htm or 60225-h.zip ***** -This and all associated files of various formats will be found in: - http://www.gutenberg.org/6/0/2/2/60225/ - -Produced by deaurider, Charlie Howard, and the Online -Distributed Proofreading Team at http://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive) - -Updated editions will replace the previous one--the old editions will -be renamed. - -Creating the works from print editions not protected by U.S. copyright -law means that no one owns a United States copyright in these works, -so the Foundation (and you!) can copy and distribute it in the United -States without permission and without paying copyright -royalties. 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