diff options
Diffstat (limited to 'old/60225-0.txt')
| -rw-r--r-- | old/60225-0.txt | 6091 |
1 files changed, 0 insertions, 6091 deletions
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. Special rules, set forth in the General Terms of Use part -of this license, apply to copying and distributing Project -Gutenberg-tm electronic works to protect the PROJECT GUTENBERG-tm -concept and trademark. Project Gutenberg is a registered trademark, -and may not be used if you charge for the eBooks, unless you receive -specific permission. If you do not charge anything for copies of this -eBook, complying with the rules is very easy. You may use this eBook -for nearly any purpose such as creation of derivative works, reports, -performances and research. They may be modified and printed and given -away--you may do practically ANYTHING in the United States with eBooks -not protected by U.S. copyright law. Redistribution is subject to the -trademark license, especially commercial redistribution. - -START: FULL LICENSE - -THE FULL PROJECT GUTENBERG LICENSE -PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK - -To protect the Project Gutenberg-tm mission of promoting the free -distribution of electronic works, by using or distributing this work -(or any other work associated in any way with the phrase "Project -Gutenberg"), you agree to comply with all the terms of the Full -Project Gutenberg-tm License available with this file or online at -www.gutenberg.org/license. - -Section 1. General Terms of Use and Redistributing Project -Gutenberg-tm electronic works - -1.A. By reading or using any part of this Project Gutenberg-tm -electronic work, you indicate that you have read, understand, agree to -and accept all the terms of this license and intellectual property -(trademark/copyright) agreement. If you do not agree to abide by all -the terms of this agreement, you must cease using and return or -destroy all copies of Project Gutenberg-tm electronic works in your -possession. If you paid a fee for obtaining a copy of or access to a -Project Gutenberg-tm electronic work and you do not agree to be bound -by the terms of this agreement, you may obtain a refund from the -person or entity to whom you paid the fee as set forth in paragraph -1.E.8. - -1.B. "Project Gutenberg" is a registered trademark. It may only be -used on or associated in any way with an electronic work by people who -agree to be bound by the terms of this agreement. There are a few -things that you can do with most Project Gutenberg-tm electronic works -even without complying with the full terms of this agreement. See -paragraph 1.C below. There are a lot of things you can do with Project -Gutenberg-tm electronic works if you follow the terms of this -agreement and help preserve free future access to Project Gutenberg-tm -electronic works. See paragraph 1.E below. - -1.C. The Project Gutenberg Literary Archive Foundation ("the -Foundation" or PGLAF), owns a compilation copyright in the collection -of Project Gutenberg-tm electronic works. Nearly all the individual -works in the collection are in the public domain in the United -States. If an individual work is unprotected by copyright law in the -United States and you are located in the United States, we do not -claim a right to prevent you from copying, distributing, performing, -displaying or creating derivative works based on the work as long as -all references to Project Gutenberg are removed. Of course, we hope -that you will support the Project Gutenberg-tm mission of promoting -free access to electronic works by freely sharing Project Gutenberg-tm -works in compliance with the terms of this agreement for keeping the -Project Gutenberg-tm name associated with the work. You can easily -comply with the terms of this agreement by keeping this work in the -same format with its attached full Project Gutenberg-tm License when -you share it without charge with others. - -1.D. The copyright laws of the place where you are located also govern -what you can do with this work. Copyright laws in most countries are -in a constant state of change. If you are outside the United States, -check the laws of your country in addition to the terms of this -agreement before downloading, copying, displaying, performing, -distributing or creating derivative works based on this work or any -other Project Gutenberg-tm work. The Foundation makes no -representations concerning the copyright status of any work in any -country outside the United States. - -1.E. Unless you have removed all references to Project Gutenberg: - -1.E.1. The following sentence, with active links to, or other -immediate access to, the full Project Gutenberg-tm License must appear -prominently whenever any copy of a Project Gutenberg-tm work (any work -on which the phrase "Project Gutenberg" appears, or with which the -phrase "Project Gutenberg" is associated) is accessed, displayed, -performed, viewed, copied or distributed: - - 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. - -1.E.2. If an individual Project Gutenberg-tm electronic work is -derived from texts not protected by U.S. copyright law (does not -contain a notice indicating that it is posted with permission of the -copyright holder), the work can be copied and distributed to anyone in -the United States without paying any fees or charges. If you are -redistributing or providing access to a work with the phrase "Project -Gutenberg" associated with or appearing on the work, you must comply -either with the requirements of paragraphs 1.E.1 through 1.E.7 or -obtain permission for the use of the work and the Project Gutenberg-tm -trademark as set forth in paragraphs 1.E.8 or 1.E.9. - -1.E.3. If an individual Project Gutenberg-tm electronic work is posted -with the permission of the copyright holder, your use and distribution -must comply with both paragraphs 1.E.1 through 1.E.7 and any -additional terms imposed by the copyright holder. Additional terms -will be linked to the Project Gutenberg-tm License for all works -posted with the permission of the copyright holder found at the -beginning of this work. - -1.E.4. Do not unlink or detach or remove the full Project Gutenberg-tm -License terms from this work, or any files containing a part of this -work or any other work associated with Project Gutenberg-tm. - -1.E.5. Do not copy, display, perform, distribute or redistribute this -electronic work, or any part of this electronic work, without -prominently displaying the sentence set forth in paragraph 1.E.1 with -active links or immediate access to the full terms of the Project -Gutenberg-tm License. - -1.E.6. You may convert to and distribute this work in any binary, -compressed, marked up, nonproprietary or proprietary form, including -any word processing or hypertext form. However, if you provide access -to or distribute copies of a Project Gutenberg-tm work in a format -other than "Plain Vanilla ASCII" or other format used in the official -version posted on the official Project Gutenberg-tm web site -(www.gutenberg.org), you must, at no additional cost, fee or expense -to the user, provide a copy, a means of exporting a copy, or a means -of obtaining a copy upon request, of the work in its original "Plain -Vanilla ASCII" or other form. Any alternate format must include the -full Project Gutenberg-tm License as specified in paragraph 1.E.1. - -1.E.7. Do not charge a fee for access to, viewing, displaying, -performing, copying or distributing any Project Gutenberg-tm works -unless you comply with paragraph 1.E.8 or 1.E.9. - -1.E.8. You may charge a reasonable fee for copies of or providing -access to or distributing Project Gutenberg-tm electronic works -provided that - -* You pay a royalty fee of 20% of the gross profits you derive from - the use of Project Gutenberg-tm works calculated using the method - you already use to calculate your applicable taxes. The fee is owed - to the owner of the Project Gutenberg-tm trademark, but he has - agreed to donate royalties under this paragraph to the Project - Gutenberg Literary Archive Foundation. Royalty payments must be paid - within 60 days following each date on which you prepare (or are - legally required to prepare) your periodic tax returns. Royalty - payments should be clearly marked as such and sent to the Project - Gutenberg Literary Archive Foundation at the address specified in - Section 4, "Information about donations to the Project Gutenberg - Literary Archive Foundation." - -* You provide a full refund of any money paid by a user who notifies - you in writing (or by e-mail) within 30 days of receipt that s/he - does not agree to the terms of the full Project Gutenberg-tm - License. You must require such a user to return or destroy all - copies of the works possessed in a physical medium and discontinue - all use of and all access to other copies of Project Gutenberg-tm - works. - -* You provide, in accordance with paragraph 1.F.3, a full refund of - any money paid for a work or a replacement copy, if a defect in the - electronic work is discovered and reported to you within 90 days of - receipt of the work. - -* You comply with all other terms of this agreement for free - distribution of Project Gutenberg-tm works. - -1.E.9. If you wish to charge a fee or distribute a Project -Gutenberg-tm electronic work or group of works on different terms than -are set forth in this agreement, you must obtain permission in writing -from both the Project Gutenberg Literary Archive Foundation and The -Project Gutenberg Trademark LLC, the owner of the Project Gutenberg-tm -trademark. Contact the Foundation as set forth in Section 3 below. - -1.F. - -1.F.1. Project Gutenberg volunteers and employees expend considerable -effort to identify, do copyright research on, transcribe and proofread -works not protected by U.S. copyright law in creating the Project -Gutenberg-tm collection. Despite these efforts, Project Gutenberg-tm -electronic works, and the medium on which they may be stored, may -contain "Defects," such as, but not limited to, incomplete, inaccurate -or corrupt data, transcription errors, a copyright or other -intellectual property infringement, a defective or damaged disk or -other medium, a computer virus, or computer codes that damage or -cannot be read by your equipment. - -1.F.2. LIMITED WARRANTY, DISCLAIMER OF DAMAGES - Except for the "Right -of Replacement or Refund" described in paragraph 1.F.3, the Project -Gutenberg Literary Archive Foundation, the owner of the Project -Gutenberg-tm trademark, and any other party distributing a Project -Gutenberg-tm electronic work under this agreement, disclaim all -liability to you for damages, costs and expenses, including legal -fees. YOU AGREE THAT YOU HAVE NO REMEDIES FOR NEGLIGENCE, STRICT -LIABILITY, BREACH OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE -PROVIDED IN PARAGRAPH 1.F.3. YOU AGREE THAT THE FOUNDATION, THE -TRADEMARK OWNER, AND ANY DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE -LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE OR -INCIDENTAL DAMAGES EVEN IF YOU GIVE NOTICE OF THE POSSIBILITY OF SUCH -DAMAGE. - -1.F.3. LIMITED RIGHT OF REPLACEMENT OR REFUND - If you discover a -defect in this electronic work within 90 days of receiving it, you can -receive a refund of the money (if any) you paid for it by sending a -written explanation to the person you received the work from. If you -received the work on a physical medium, you must return the medium -with your written explanation. The person or entity that provided you -with the defective work may elect to provide a replacement copy in -lieu of a refund. If you received the work electronically, the person -or entity providing it to you may choose to give you a second -opportunity to receive the work electronically in lieu of a refund. If -the second copy is also defective, you may demand a refund in writing -without further opportunities to fix the problem. - -1.F.4. Except for the limited right of replacement or refund set forth -in paragraph 1.F.3, this work is provided to you 'AS-IS', WITH NO -OTHER WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT -LIMITED TO WARRANTIES OF MERCHANTABILITY OR FITNESS FOR ANY PURPOSE. - -1.F.5. Some states do not allow disclaimers of certain implied -warranties or the exclusion or limitation of certain types of -damages. If any disclaimer or limitation set forth in this agreement -violates the law of the state applicable to this agreement, the -agreement shall be interpreted to make the maximum disclaimer or -limitation permitted by the applicable state law. The invalidity or -unenforceability of any provision of this agreement shall not void the -remaining provisions. - -1.F.6. INDEMNITY - You agree to indemnify and hold the Foundation, the -trademark owner, any agent or employee of the Foundation, anyone -providing copies of Project Gutenberg-tm electronic works in -accordance with this agreement, and any volunteers associated with the -production, promotion and distribution of Project Gutenberg-tm -electronic works, harmless from all liability, costs and expenses, -including legal fees, that arise directly or indirectly from any of -the following which you do or cause to occur: (a) distribution of this -or any Project Gutenberg-tm work, (b) alteration, modification, or -additions or deletions to any Project Gutenberg-tm work, and (c) any -Defect you cause. - -Section 2. Information about the Mission of Project Gutenberg-tm - -Project Gutenberg-tm is synonymous with the free distribution of -electronic works in formats readable by the widest variety of -computers including obsolete, old, middle-aged and new computers. It -exists because of the efforts of hundreds of volunteers and donations -from people in all walks of life. - -Volunteers and financial support to provide volunteers with the -assistance they need are critical to reaching Project Gutenberg-tm's -goals and ensuring that the Project Gutenberg-tm collection will -remain freely available for generations to come. In 2001, the Project -Gutenberg Literary Archive Foundation was created to provide a secure -and permanent future for Project Gutenberg-tm and future -generations. To learn more about the Project Gutenberg Literary -Archive Foundation and how your efforts and donations can help, see -Sections 3 and 4 and the Foundation information page at -www.gutenberg.org - - - -Section 3. Information about the Project Gutenberg Literary Archive Foundation - -The Project Gutenberg Literary Archive Foundation is a non profit -501(c)(3) educational corporation organized under the laws of the -state of Mississippi and granted tax exempt status by the Internal -Revenue Service. The Foundation's EIN or federal tax identification -number is 64-6221541. Contributions to the Project Gutenberg Literary -Archive Foundation are tax deductible to the full extent permitted by -U.S. federal laws and your state's laws. - -The Foundation's principal office is in Fairbanks, Alaska, with the -mailing address: PO Box 750175, Fairbanks, AK 99775, but its -volunteers and employees are scattered throughout numerous -locations. Its business office is located at 809 North 1500 West, Salt -Lake City, UT 84116, (801) 596-1887. Email contact links and up to -date contact information can be found at the Foundation's web site and -official page at www.gutenberg.org/contact - -For additional contact information: - - Dr. Gregory B. Newby - Chief Executive and Director - gbnewby@pglaf.org - -Section 4. Information about Donations to the Project Gutenberg -Literary Archive Foundation - -Project Gutenberg-tm depends upon and cannot survive without wide -spread public support and donations to carry out its mission of -increasing the number of public domain and licensed works that can be -freely distributed in machine readable form accessible by the widest -array of equipment including outdated equipment. Many small donations -($1 to $5,000) are particularly important to maintaining tax exempt -status with the IRS. - -The Foundation is committed to complying with the laws regulating -charities and charitable donations in all 50 states of the United -States. Compliance requirements are not uniform and it takes a -considerable effort, much paperwork and many fees to meet and keep up -with these requirements. We do not solicit donations in locations -where we have not received written confirmation of compliance. To SEND -DONATIONS or determine the status of compliance for any particular -state visit www.gutenberg.org/donate - -While we cannot and do not solicit contributions from states where we -have not met the solicitation requirements, we know of no prohibition -against accepting unsolicited donations from donors in such states who -approach us with offers to donate. - -International donations are gratefully accepted, but we cannot make -any statements concerning tax treatment of donations received from -outside the United States. U.S. laws alone swamp our small staff. - -Please check the Project Gutenberg Web pages for current donation -methods and addresses. Donations are accepted in a number of other -ways including checks, online payments and credit card donations. To -donate, please visit: www.gutenberg.org/donate - -Section 5. General Information About Project Gutenberg-tm electronic works. - -Professor Michael S. Hart was the originator of the Project -Gutenberg-tm concept of a library of electronic works that could be -freely shared with anyone. For forty years, he produced and -distributed Project Gutenberg-tm eBooks with only a loose network of -volunteer support. - -Project Gutenberg-tm eBooks are often created from several printed -editions, all of which are confirmed as not protected by copyright in -the U.S. unless a copyright notice is included. Thus, we do not -necessarily keep eBooks in compliance with any particular paper -edition. - -Most people start at our Web site which has the main PG search -facility: www.gutenberg.org - -This Web site includes information about Project Gutenberg-tm, -including how to make donations to the Project Gutenberg Literary -Archive Foundation, how to help produce our new eBooks, and how to -subscribe to our email newsletter to hear about new eBooks. - |