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diff --git a/1708.txt b/1708.txt new file mode 100644 index 0000000..ebb6297 --- /dev/null +++ b/1708.txt @@ -0,0 +1,8464 @@ +The Project Gutenberg EBook of A History of Science, Volume 4(of 5), by +Henry Smith Williams + +This eBook is for the use of anyone anywhere 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 + + +Title: A History of Science, Volume 4(of 5) + +Author: Henry Smith Williams + +Release Date: April, 1999 [Etext #1708] +Posting Date: November 18, 2009 + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK HISTORY OF SCIENCE, V4 *** + + + + +Produced by Charles Keller + + + + + +A HISTORY OF SCIENCE + + +By Henry Smith Williams, M.D., LL.D. + +Assisted By Edward H. Williams, M.D. + +In Five Volumes + +Volume IV. + + +MODERN DEVELOPMENT OF THE CHEMICAL AND BIOLOGICAL SCIENCES + + + + +BOOK IV. MODERN DEVELOPMENT OF THE CHEMICAL AND BIOLOGICAL SCIENCES + +AS regards chronology, the epoch covered in the present volume is +identical with that viewed in the preceding one. But now as regards +subject matter we pass on to those diverse phases of the physical world +which are the field of the chemist, and to those yet more intricate +processes which have to do with living organisms. So radical are the +changes here that we seem to be entering new worlds; and yet, here as +before, there are intimations of the new discoveries away back in the +Greek days. The solution of the problem of respiration will remind +us that Anaxagoras half guessed the secret; and in those diversified +studies which tell us of the Daltonian atom in its wonderful +transmutations, we shall be reminded again of the Clazomenian +philosopher and his successor Democritus. + +Yet we should press the analogy much too far were we to intimate that +the Greek of the elder day or any thinker of a more recent period had +penetrated, even in the vaguest way, all of the mysteries that the +nineteenth century has revealed in the fields of chemistry and biology. +At the very most the insight of those great Greeks and of the wonderful +seventeenth-century philosophers who so often seemed on the verge of our +later discoveries did no more than vaguely anticipate their successors +of this later century. To gain an accurate, really specific knowledge of +the properties of elementary bodies was reserved for the chemists of a +recent epoch. The vague Greek questionings as to organic evolution were +world-wide from the precise inductions of a Darwin. If the mediaeval +Arabian endeavored to dull the knife of the surgeon with the use of +drugs, his results hardly merit to be termed even an anticipation +of modern anaesthesia. And when we speak of preventive medicine--of +bacteriology in all its phases--we have to do with a marvellous field of +which no previous generation of men had even the slightest inkling. + +All in all, then, those that lie before us are perhaps the most +wonderful and the most fascinating of all the fields of science. As +the chapters of the preceding book carried us out into a macrocosm of +inconceivable magnitude, our present studies are to reveal a microcosm +of equally inconceivable smallness. As the studies of the physicist +attempted to reveal the very nature of matter and of energy, we have now +to seek the solution of the yet more inscrutable problems of life and of +mind. + + + + +I. THE PHLOGISTON THEORY IN CHEMISTRY + +The development of the science of chemistry from the "science" of +alchemy is a striking example of the complete revolution in the attitude +of observers in the field of science. As has been pointed out in a +preceding chapter, the alchemist, having a preconceived idea of how +things should be, made all his experiments to prove his preconceived +theory; while the chemist reverses this attitude of mind and bases his +conceptions on the results of his laboratory experiments. In short, +chemistry is what alchemy never could be, an inductive science. But +this transition from one point of view to an exactly opposite one was +necessarily a very slow process. Ideas that have held undisputed sway +over the minds of succeeding generations for hundreds of years cannot +be overthrown in a moment, unless the agent of such an overthrow be so +obvious that it cannot be challenged. The rudimentary chemistry that +overthrew alchemy had nothing so obvious and palpable. + +The great first step was the substitution of the one principle, +phlogiston, for the three principles, salt, sulphur, and mercury. We +have seen how the experiment of burning or calcining such a metal +as lead "destroyed" the lead as such, leaving an entirely different +substance in its place, and how the original metal could be restored by +the addition of wheat to the calcined product. To the alchemist this was +"mortification" and "revivification" of the metal. For, as pointed +out by Paracelsus, "anything that could be killed by man could also be +revivified by him, although this was not possible to the things killed +by God." The burning of such substances as wood, wax, oil, etc., was +also looked upon as the same "killing" process, and the fact that the +alchemist was unable to revivify them was regarded as simply the lack of +skill on his part, and in no wise affecting the theory itself. + +But the iconoclastic spirit, if not the acceptance of all the teachings, +of the great Paracelsus had been gradually taking root among the better +class of alchemists, and about the middle of the seventeenth century +Robert Boyle (1626-1691) called attention to the possibility of making +a wrong deduction from the phenomenon of the calcination of the metals, +because of a very important factor, the action of the air, which was +generally overlooked. And he urged his colleagues of the laboratories to +give greater heed to certain other phenomena that might pass unnoticed +in the ordinary calcinating process. In his work, The Sceptical Chemist, +he showed the reasons for doubting the threefold constitution of matter; +and in his General History of the Air advanced some novel and carefully +studied theories as to the composition of the atmosphere. This was an +important step, and although Boyle is not directly responsible for the +phlogiston theory, it is probable that his experiments on the atmosphere +influenced considerably the real founders, Becker and Stahl. + +Boyle gave very definitely his idea of how he thought air might be +composed. "I conjecture that the atmospherical air consists of three +different kinds of corpuscles," he says; "the first, those numberless +particles which, in the form of vapors or dry exhalations, ascend +from the earth, water, minerals, vegetables, animals, etc.; in a word, +whatever substances are elevated by the celestial or subterraneal heat, +and thence diffused into the atmosphere. The second may be yet more +subtle, and consist of those exceedingly minute atoms, the magnetical +effluvia of the earth, with other innumerable particles sent out from +the bodies of the celestial luminaries, and causing, by their influence, +the idea of light in us. The third sort is its characteristic and +essential property, I mean permanently elastic parts. Various hypotheses +may be framed relating to the structure of these later particles of the +air. They might be resembled to the springs of watches, coiled up and +endeavoring to restore themselves; to wool, which, being compressed, +has an elastic force; to slender wires of different substances, +consistencies, lengths, and thickness; in greater curls or less, +near to, or remote from each other, etc., yet all continuing springy, +expansible, and compressible. Lastly, they may also be compared to the +thin shavings of different kinds of wood, various in their lengths, +breadth, and thickness. And this, perhaps, will seem the most eligible +hypothesis, because it, in some measure, illustrates the production +of the elastic particles we are considering. For no art or curious +instruments are required to make these shavings whose curls are in no +wise uniform, but seemingly casual; and what is more remarkable, bodies +that before seemed unelastic, as beams and blocks, will afford them."(1) + +Although this explanation of the composition of the air is most crude, +it had the effect of directing attention to the fact that the +atmosphere is not "mere nothingness," but a "something" with a +definite composition, and this served as a good foundation for future +investigations. To be sure, Boyle was neither the first nor the only +chemist who had suspected that the air was a mixture of gases, and not +a simple one, and that only certain of these gases take part in the +process of calcination. Jean Rey, a French physician, and John Mayow, an +Englishman, had preformed experiments which showed conclusively that the +air was not a simple substance; but Boyle's work was better known, and +in its effect probably more important. But with all Boyle's explanations +of the composition of air, he still believed that there was an +inexplicable something, a "vital substance," which he was unable to +fathom, and which later became the basis of Stahl's phlogiston theory. +Commenting on this mysterious substance, Boyle says: "The difficulty +we find in keeping flame and fire alive, though but for a little time, +without air, renders it suspicious that there be dispersed through the +rest of the atmosphere some odd substance, either of a solar, astral, or +other foreign nature; on account of which the air is so necessary to the +substance of flame!" It was this idea that attracted the attention +of George Ernst Stahl (1660-1734), a professor of medicine in the +University of Halle, who later founded his new theory upon it. Stahl's +theory was a development of an earlier chemist, Johann Joachim Becker +(1635-1682), in whose footsteps he followed and whose experiments he +carried further. + +In many experiments Stahl had been struck with the fact that certain +substances, while differing widely, from one another in many respects, +were alike in combustibility. From this he argued that all combustible +substances must contain a common principle, and this principle he named +phlogiston. This phlogiston he believed to be intimately associated in +combination with other substances in nature, and in that condition not +perceivable by the senses; but it was supposed to escape as a substance +burned, and become apparent to the senses as fire or flame. In other +words, phlogiston was something imprisoned in a combustible structure +(itself forming part of the structure), and only liberated when this +structure was destroyed. Fire, or flame, was FREE phlogiston, while the +imprisoned phlogiston was called COMBINED PHLOGISTON, or combined fire. +The peculiar quality of this strange substance was that it disliked +freedom and was always striving to conceal itself in some combustible +substance. Boyle's tentative suggestion that heat was simply motion was +apparently not accepted by Stahl, or perhaps it was unknown to him. + +According to the phlogistic theory, the part remaining after a substance +was burned was simply the original substance deprived of phlogiston. To +restore the original combustible substance, it was necessary to heat the +residue of the combustion with something that burned easily, so that the +freed phlogiston might again combine with the ashes. This was explained +by the supposition that the more combustible a substance was the more +phlogiston it contained, and since free phlogiston sought always to +combine with some suitable substance, it was only necessary to mix the +phlogisticating agents, such as charcoal, phosphorus, oils, fats, etc., +with the ashes of the original substance, and heat the mixture, the +phlogiston thus freed uniting at once with the ashes. This theory fitted +very nicely as applied to the calcined lead revivified by the grains of +wheat, although with some other products of calcination it did not seem +to apply at all. + +It will be seen from this that the phlogistic theory was a step towards +chemistry and away from alchemy. It led away from the idea of a "spirit" +in metals that could not be seen, felt, or appreciated by any of the +senses, and substituted for it a principle which, although a falsely +conceived one, was still much more tangible than the "spirit," since it +could be seen and felt as free phlogiston and weighed and measured as +combined phlogiston. The definiteness of the statement that a metal, +for example, was composed of phlogiston and an element was much less +enigmatic, even if wrong, than the statement of the alchemist that +"metals are produced by the spiritual action of the three principles, +salt, mercury, sulphur"--particularly when it is explained that salt, +mercury, and sulphur were really not what their names implied, and that +there was no universally accepted belief as to what they really were. + +The metals, which are now regarded as elementary bodies, were considered +compounds by the phlogistians, and they believed that the calcining of +a metal was a process of simplification. They noted, however, that the +remains of calcination weighed more than the original product, and the +natural inference from this would be that the metal must have taken in +some substance rather than have given off anything. But the phlogistians +had not learned the all-important significance of weights, and their +explanation of variation in weight was either that such gain or loss +was an unimportant "accident" at best, or that phlogiston, being light, +tended to lighten any substance containing it, so that driving it out of +the metal by calcination naturally left the residue heavier. + +At first the phlogiston theory seemed to explain in an indisputable way +all the known chemical phenomena. Gradually, however, as experiments +multiplied, it became evident that the plain theory as stated by Stahl +and his followers failed to explain satisfactorily certain laboratory +reactions. To meet these new conditions, certain modifications were +introduced from time to time, giving the theory a flexibility that +would allow it to cover all cases. But as the number of inexplicable +experiments continued to increase, and new modifications to the theory +became necessary, it was found that some of these modifications were +directly contradictory to others, and thus the simple theory became +too cumbersome from the number of its modifications. Its supporters +disagreed among themselves, first as to the explanation of certain +phenomena that did not seem to accord with the phlogistic theory, and +a little later as to the theory itself. But as yet there was no +satisfactory substitute for this theory, which, even if unsatisfactory, +seemed better than anything that had gone before or could be suggested. + +But the good effects of the era of experimental research, to which the +theory of Stahl had given such an impetus, were showing in the attitude +of the experimenters. The works of some of the older writers, such +as Boyle and Hooke, were again sought out in their dusty corners and +consulted, and their surmises as to the possible mixture of various +gases in the air were more carefully considered. Still the phlogiston +theory was firmly grounded in the minds of the philosophers, who can +hardly be censured for adhering to it, at least until some satisfactory +substitute was offered. The foundation for such a theory was finally +laid, as we shall see presently, by the work of Black, Priestley, +Cavendish, and Lavoisier, in the eighteenth century, but the phlogiston +theory cannot be said to have finally succumbed until the opening years +of the nineteenth century. + + + + +II. THE BEGINNINGS OF MODERN CHEMISTRY + +THE "PNEUMATIC" CHEMISTS + +Modern chemistry may be said to have its beginning with the work of +Stephen Hales (1677-1761), who early in the eighteenth century began his +important study of the elasticity of air. Departing from the point of +view of most of the scientists of the time, he considered air to be "a +fine elastic fluid, with particles of very different nature floating in +it"; and he showed that these "particles" could be separated. He pointed +out, also, that various gases, or "airs," as he called them, were +contained in many solid substances. The importance of his work, however, +lies in the fact that his general studies were along lines leading away +from the accepted doctrines of the time, and that they gave the impetus +to the investigation of the properties of gases by such chemists as +Black, Priestley, Cavendish, and Lavoisier, whose specific discoveries +are the foundation-stones of modern chemistry. + + +JOSEPH BLACK + +The careful studies of Hales were continued by his younger confrere, Dr. +Joseph Black (1728-1799), whose experiments in the weights of gases and +other chemicals were first steps in quantitative chemistry. But even +more important than his discoveries of chemical properties in general +was his discovery of the properties of carbonic-acid gas. + +Black had been educated for the medical profession in the University of +Glasgow, being a friend and pupil of the famous Dr. William Cullen. But +his liking was for the chemical laboratory rather than for the practice +of medicine. Within three years after completing his medical course, +and when only twenty-three years of age, he made the discovery of the +properties of carbonic acid, which he called by the name of "fixed air." +After discovering this gas, Black made a long series of experiments, +by which he was able to show how widely it was distributed throughout +nature. Thus, in 1757, he discovered that the bubbles given off in +the process of brewing, where there was vegetable fermentation, were +composed of it. To prove this, he collected the contents of these +bubbles in a bottle containing lime-water. When this bottle was +shaken violently, so that the lime-water and the carbonic acid became +thoroughly mixed, an insoluble white powder was precipitated from the +solution, the carbonic acid having combined chemically with the lime +to form the insoluble calcium carbonate, or chalk. This experiment +suggested another. Fixing a piece of burning charcoal in the end of a +bellows, he arranged a tube so that the gas coming from the charcoal +would pass through the lime-water, and, as in the case of the bubbles +from the brewer's vat, he found that the white precipitate was thrown +down; in short, that carbonic acid was given off in combustion. Shortly +after, Black discovered that by blowing through a glass tube inserted +into lime-water, chalk was precipitated, thus proving that carbonic acid +was being constantly thrown off in respiration. + +The effect of Black's discoveries was revolutionary, and the attitude +of mind of the chemists towards gases, or "airs," was changed from that +time forward. Most of the chemists, however, attempted to harmonize the +new facts with the older theories--to explain all the phenomena on the +basis of the phlogiston theory, which was still dominant. But while many +of Black's discoveries could not be made to harmonize with that +theory, they did not directly overthrow it. It required the additional +discoveries of some of Black's fellow-scientists to complete its +downfall, as we shall see. + + +HENRY CAVENDISH + +This work of Black's was followed by the equally important work of +his former pupil, Henry Cavendish (1731-1810), whose discovery of the +composition of many substances, notably of nitric acid and of water, +was of great importance, adding another link to the important chain of +evidence against the phlogiston theory. Cavendish is one of the most +eccentric figures in the history of science, being widely known in his +own time for his immense wealth and brilliant intellect, and also for +his peculiarities and his morbid sensibility, which made him dread +society, and probably did much in determining his career. Fortunately +for him, and incidentally for the cause of science, he was able to +pursue laboratory investigations without being obliged to mingle with +his dreaded fellow-mortals, his every want being provided for by the +immense fortune inherited from his father and an uncle. + +When a young man, as a pupil of Dr. Black, he had become imbued with the +enthusiasm of his teacher, continuing Black's investigations as to the +properties of carbonic-acid gas when free and in combination. One of his +first investigations was reported in 1766, when he communicated to +the Royal Society his experiments for ascertaining the properties of +carbonic-acid and hydrogen gas, in which he first showed the possibility +of weighing permanently elastic fluids, although Torricelli had before +this shown the relative weights of a column of air and a column of +mercury. Other important experiments were continued by Cavendish, and +in 1784 he announced his discovery of the composition of water, thus +robbing it of its time-honored position as an "element." But his +claim to priority in this discovery was at once disputed by his +fellow-countryman James Watt and by the Frenchman Lavoisier. Lavoisier's +claim was soon disallowed even by his own countrymen, but for many +years a bitter controversy was carried on by the partisans of Watt and +Cavendish. The two principals, however, seem never to have entered +into this controversy with anything like the same ardor as some of their +successors, as they remained on the best of terms.(1) It is certain, at +any rate, that Cavendish announced his discovery officially before Watt +claimed that the announcement had been previously made by him, "and, +whether right or wrong, the honor of scientific discoveries seems to be +accorded naturally to the man who first publishes a demonstration of his +discovery." Englishmen very generally admit the justness of Cavendish's +claim, although the French scientist Arago, after reviewing the evidence +carefully in 1833, decided in favor of Watt. + +It appears that something like a year before Cavendish made known his +complete demonstration of the composition of water, Watt communicated +to the Royal Society a suggestion that water was composed of +"dephlogisticated air (oxygen) and phlogiston (hydrogen) deprived of +part of its latent heat." Cavendish knew of the suggestion, but in his +experiments refuted the idea that the hydrogen lost any of its latent +heat. Furthermore, Watt merely suggested the possible composition +without proving it, although his idea was practically correct, if we can +rightly interpret the vagaries of the nomenclature then in use. But +had Watt taken the steps to demonstrate his theory, the great "Water +Controversy" would have been avoided. Cavendish's report of his +discovery to the Royal Society covers something like forty pages of +printed matter. In this he shows how, by passing an electric spark +through a closed jar containing a mixture of hydrogen gas and oxygen, +water is invariably formed, apparently by the union of the two gases. +The experiment was first tried with hydrogen and common air, the oxygen +of the air uniting with the hydrogen to form water, leaving the nitrogen +of the air still to be accounted for. With pure oxygen and hydrogen, +however, Cavendish found that pure water was formed, leaving slight +traces of any other, substance which might not be interpreted as being +Chemical impurities. There was only one possible explanation of this +phenomenon--that hydrogen and oxygen, when combined, form water. + +"By experiments with the globe it appeared," wrote Cavendish, "that when +inflammable and common air are exploded in a proper proportion, almost +all the inflammable air, and near one-fifth the common air, lose their +elasticity and are condensed into dew. And by this experiment it appears +that this dew is plain water, and consequently that almost all the +inflammable air is turned into pure water. + +"In order to examine the nature of the matter condensed on firing a +mixture of dephlogisticated and inflammable air, I took a glass +globe, holding 8800 grain measures, furnished with a brass cock and an +apparatus for firing by electricity. This globe was well exhausted by +an air-pump, and then filled with a mixture of inflammable and +dephlogisticated air by shutting the cock, fastening the bent glass tube +into its mouth, and letting up the end of it into a glass jar inverted +into water and containing a mixture of 19,500 grain measures of +dephlogisticated air, and 37,000 of inflammable air; so that, upon +opening the cock, some of this mixed air rushed through the bent tube +and filled the globe. The cock was then shut and the included air fired +by electricity, by means of which almost all of it lost its elasticity +(was condensed into water vapors). The cock was then again opened so as +to let in more of the same air to supply the place of that destroyed by +the explosion, which was again fired, and the operation continued till +almost the whole of the mixture was let into the globe and exploded. +By this means, though the globe held not more than a sixth part of the +mixture, almost the whole of it was exploded therein without any fresh +exhaustion of the globe." + +At first this condensed matter was "acid to the taste and contained +two grains of nitre," but Cavendish, suspecting that this was due to +impurities, tried another experiment that proved conclusively that his +opinions were correct. "I therefore made another experiment," he says, +"with some more of the same air from plants in which the proportion of +inflammable air was greater, so that the burnt air was almost completely +phlogisticated, its standard being one-tenth. The condensed liquor was +then not at all acid, but seemed pure water." + +From these experiments he concludes "that when a mixture of inflammable +and dephlogisticated air is exploded, in such proportions that the burnt +air is not much phlogisticated, the condensed liquor contains a little +acid which is always of the nitrous kind, whatever substance the +dephlogisticated air is procured from; but if the proportion be such +that the burnt air is almost entirely phlogisticated, the condensed +liquor is not at all acid, but seems pure water, without any addition +whatever."(2) + +These same experiments, which were undertaken to discover the +composition of water, led him to discover also the composition of nitric +acid. He had observed that, in the combustion of hydrogen gas with +common air, the water was slightly tinged with acid, but that this +was not the case when pure oxygen gas was used. Acting upon this +observation, he devised an experiment to determine the nature of this +acid. He constructed an apparatus whereby an electric spark was passed +through a vessel containing common air. After this process had been +carried on for several weeks a small amount of liquid was formed. This +liquid combined with a solution of potash to form common nitre, which +"detonated with charcoal, sparkled when paper impregnated with it was +burned, and gave out nitrous fumes when sulphuric acid was poured on +it." In other words, the liquid was shown to be nitric acid. Now, since +nothing but pure air had been used in the initial experiment, and since +air is composed of nitrogen and oxygen, there seemed no room to doubt +that nitric acid is a combination of nitrogen and oxygen. + +This discovery of the nature of nitric acid seems to have been about the +last work of importance that Cavendish did in the field of chemistry, +although almost to the hour of his death he was constantly occupied with +scientific observations. Even in the last moments of his life this habit +asserted itself, according to Lord Brougham. "He died on March 10, 1810, +after a short illness, probably the first, as well as the last, which he +ever suffered. His habit of curious observation continued to the end. +He was desirous of marking the progress of the disease and the gradual +extinction of the vital powers. With these ends in view, that he might +not be disturbed, he desired to be left alone. His servant, returning +sooner than he had wished, was ordered again to leave the chamber of +death, and when he came back a second time he found his master had +expired."(3) + + +JOSEPH PRIESTLEY + +While the opulent but diffident Cavendish was making his important +discoveries, another Englishman, a poor country preacher named Joseph +Priestley (1733-1804) was not only rivalling him, but, if anything, +outstripping him in the pursuit of chemical discoveries. In 1761 this +young minister was given a position as tutor in a nonconformist academy +at Warrington, and here, for six years, he was able to pursue his +studies in chemistry and electricity. In 1766, while on a visit to +London, he met Benjamin Franklin, at whose suggestion he published his +History of Electricity. From this time on he made steady progress in +scientific investigations, keeping up his ecclesiastical duties at the +same time. In 1780 he removed to Birmingham, having there for associates +such scientists as James Watt, Boulton, and Erasmus Darwin. + +Eleven years later, on the anniversary of the fall of the Bastile in +Paris, a fanatical mob, knowing Priestley's sympathies with the +French revolutionists, attacked his house and chapel, burning both and +destroying a great number of valuable papers and scientific instruments. +Priestley and his family escaped violence by flight, but his most +cherished possessions were destroyed; and three years later he quitted +England forever, removing to the United States, whose struggle for +liberty he had championed. The last ten years of his life were spent +at Northumberland, Pennsylvania, where he continued his scientific +researches. + +Early in his scientific career Priestley began investigations upon the +"fixed air" of Dr. Black, and, oddly enough, he was stimulated to this +by the same thing that had influenced Black--that is, his residence in +the immediate neighborhood of a brewery. It was during the course of a +series of experiments on this and other gases that he made his greatest +discovery, that of oxygen, or "dephlogisticated air," as he called +it. The story of this important discovery is probably best told in +Priestley's own words: + +"There are, I believe, very few maxims in philosophy that have laid +firmer hold upon the mind than that air, meaning atmospheric air, is a +simple elementary substance, indestructible and unalterable, at least as +much so as water is supposed to be. In the course of my inquiries I +was, however, soon satisfied that atmospheric air is not an unalterable +thing; for that, according to my first hypothesis, the phlogiston with +which it becomes loaded from bodies burning in it, and the animals +breathing it, and various other chemical processes, so far alters +and depraves it as to render it altogether unfit for inflammation, +respiration, and other purposes to which it is subservient; and I had +discovered that agitation in the water, the process of vegetation, and +probably other natural processes, restore it to its original purity.... + +"Having procured a lens of twelve inches diameter and twenty inches +local distance, I proceeded with the greatest alacrity, by the help of +it, to discover what kind of air a great variety of substances would +yield, putting them into the vessel, which I filled with quicksilver, +and kept inverted in a basin of the same .... With this apparatus, after +a variety of experiments.... on the 1st of August, 1774, I endeavored +to extract air from mercurius calcinatus per se; and I presently found +that, by means of this lens, air was expelled from it very readily. +Having got about three or four times as much as the bulk of my +materials, I admitted water to it, and found that it was not imbibed +by it. But what surprised me more than I can express was that a candle +burned in this air with a remarkably vigorous flame, very much like that +enlarged flame with which a candle burns in nitrous oxide, exposed to +iron or liver of sulphur; but as I had got nothing like this remarkable +appearance from any kind of air besides this particular modification of +vitrous air, and I knew no vitrous acid was used in the preparation of +mercurius calcinatus, I was utterly at a loss to account for it."(4) + + +The "new air" was, of course, oxygen. Priestley at once proceeded to +examine it by a long series of careful experiments, in which, as will +be seen, he discovered most of the remarkable qualities of this gas. +Continuing his description of these experiments, he says: + +"The flame of the candle, besides being larger, burned with more +splendor and heat than in that species of nitrous air; and a piece of +red-hot wood sparkled in it, exactly like paper dipped in a solution of +nitre, and it consumed very fast; an experiment that I had never thought +of trying with dephlogisticated nitrous air. + +"... I had so little suspicion of the air from the mercurius calcinatus, +etc., being wholesome, that I had not even thought of applying it to +the test of nitrous air; but thinking (as my reader must imagine I +frequently must have done) on the candle burning in it after long +agitation in water, it occurred to me at last to make the experiment; +and, putting one measure of nitrous air to two measures of this air, I +found not only that it was diminished, but that it was diminished quite +as much as common air, and that the redness of the mixture was likewise +equal to a similar mixture of nitrous and common air.... The next day I +was more surprised than ever I had been before with finding that, after +the above-mentioned mixture of nitrous air and the air from mercurius +calcinatus had stood all night,... a candle burned in it, even better +than in common air." + +A little later Priestley discovered that "dephlogisticated air... is a +principal element in the composition of acids, and may be extracted by +means of heat from many substances which contain them.... It is likewise +produced by the action of light upon green vegetables; and this seems to +be the chief means employed to preserve the purity of the atmosphere." + +This recognition of the important part played by oxygen in the +atmosphere led Priestley to make some experiments upon mice and insects, +and finally upon himself, by inhalations of the pure gas. "The feeling +in my lungs," he said, "was not sensibly different from that of common +air, but I fancied that my breathing felt peculiarly light and easy for +some time afterwards. Who can tell but that in time this pure air may +become a fashionable article in luxury?... Perhaps we may from these +experiments see that though pure dephlogisticated air might be useful as +a medicine, it might not be so proper for us in the usual healthy state +of the body." + +This suggestion as to the possible usefulness of oxygen as a medicine +was prophetic. A century later the use of oxygen had become a matter of +routine practice with many physicians. Even in Priestley's own time such +men as Dr. John Hunter expressed their belief in its efficacy in certain +conditions, as we shall see, but its value in medicine was not fully +appreciated until several generations later. + +Several years after discovering oxygen Priestley thus summarized its +properties: "It is this ingredient in the atmospheric air that enables +it to support combustion and animal life. By means of it most intense +heat may be produced, and in the purest of it animals will live nearly +five times as long as in an equal quantity of atmospheric air. In +respiration, part of this air, passing the membranes of the lungs, +unites with the blood and imparts to it its florid color, while the +remainder, uniting with phlogiston exhaled from venous blood, forms +mixed air. It is dephlogisticated air combined with water that enables +fishes to live in it."(5) + + +KARL WILHELM SCHEELE + +The discovery of oxygen was the last but most important blow to the +tottering phlogiston theory, though Priestley himself would not admit +it. But before considering the final steps in the overthrow of Stahl's +famous theory and the establishment of modern chemistry, we must review +the work of another great chemist, Karl Wilhelm Scheele (1742-1786), of +Sweden, who discovered oxygen quite independently, although later than +Priestley. In the matter of brilliant discoveries in a brief space of +time Scheele probably eclipsed all his great contemporaries. He had a +veritable genius for interpreting chemical reactions and discovering +new substances, in this respect rivalling Priestley himself. Unlike +Priestley, however, he planned all his experiments along the lines of +definite theories from the beginning, the results obtained being the +logical outcome of a predetermined plan. + +Scheele was the son of a merchant of Stralsund, Pomerania, which then +belonged to Sweden. As a boy in school he showed so little aptitude for +the study of languages that he was apprenticed to an apothecary at the +age of fourteen. In this work he became at once greatly interested, and, +when not attending to his duties in the dispensary, he was busy day and +night making experiments or studying books on chemistry. In 1775, still +employed as an apothecary, he moved to Stockholm, and soon after he sent +to Bergman, the leading chemist of Sweden, his first discovery--that of +tartaric acid, which he had isolated from cream of tartar. This was the +beginning of his career of discovery, and from that time on until his +death he sent forth accounts of new discoveries almost uninterruptedly. +Meanwhile he was performing the duties of an ordinary apothecary, and +struggling against poverty. His treatise upon Air and Fire appeared +in 1777. In this remarkable book he tells of his discovery of +oxygen--"empyreal" or "fire-air," as he calls it--which he seems to +have made independently and without ever having heard of the previous +discovery by Priestley. In this book, also, he shows that air is +composed chiefly of oxygen and nitrogen gas. + +Early in his experimental career Scheele undertook the solution of +the composition of black oxide of manganese, a substance that had long +puzzled the chemists. He not only succeeded in this, but incidentally in +the course of this series of experiments he discovered oxygen, baryta, +and chlorine, the last of far greater importance, at least commercially, +than the real object of his search. In speaking of the experiment in +which the discovery was made he says: + +"When marine (hydrochloric) acid stood over manganese in the cold it +acquired a dark reddish-brown color. As manganese does not give any +colorless solution without uniting with phlogiston (probably meaning +hydrogen), it follows that marine acid can dissolve it without this +principle. But such a solution has a blue or red color. The color is +here more brown than red, the reason being that the very finest portions +of the manganese, which do not sink so easily, swim in the red solution; +for without these fine particles the solution is red, and red mixed with +black is brown. The manganese has here attached itself so loosely to +acidum salis that the water can precipitate it, and this precipitate +behaves like ordinary manganese. When, now, the mixture of manganese and +spiritus salis was set to digest, there arose an effervescence and smell +of aqua regis."(6) + +The "effervescence" he refers to was chlorine, which he proceeded to +confine in a suitable vessel and examine more fully. He described it as +having a "quite characteristically suffocating smell," which was very +offensive. He very soon noted the decolorizing or bleaching effects of +this now product, finding that it decolorized flowers, vegetables, and +many other substances. + +Commercially this discovery of chlorine was of enormous importance and +the practical application of this new chemical in bleaching cloth soon +supplanted the old process of crofting--that is, bleaching by spreading +the cloth upon the grass. But although Scheele first pointed out the +bleaching quality of his newly discovered gas, it was the French savant, +Berthollet, who, acting upon Scheele's discovery that the new gas would +decolorize vegetables and flowers, was led to suspect that this property +might be turned to account in destroying the color of cloth. In 1785 he +read a paper before the Academy of Sciences of Paris, in which he showed +that bleaching by chlorine was entirely satisfactory, the color but +not the substance of the cloth being affected. He had experimented +previously and found that the chlorine gas was soluble in water and +could thus be made practically available for bleaching purposes. In 1786 +James Watt examined specimens of the bleached cloth made by Berthollet, +and upon his return to England first instituted the process of practical +bleaching. His process, however, was not entirely satisfactory, and, +after undergoing various modifications and improvements, it was finally +made thoroughly practicable by Mr. Tennant, who hit upon a compound of +chlorine and lime--the chloride of lime--which was a comparatively cheap +chemical product, and answered the purpose better even than chlorine +itself. + +To appreciate how momentous this discovery was to cloth manufacturers, +it should be remembered that the old process of bleaching consumed an +entire summer for the whitening of a single piece of linen; the new +process reduced the period to a few hours. To be sure, lime had been +used with fair success previous to Tennant's discovery, but successful +and practical bleaching by a solution of chloride of lime was first made +possible by him and through Scheele's discovery of chlorine. + +Until the time of Scheele the great subject of organic chemistry had +remained practically unexplored, but under the touch of his marvellous +inventive genius new methods of isolating and studying animal and +vegetable products were introduced, and a large number of acids and +other organic compounds prepared that had been hitherto unknown. His +explanations of chemical phenomena were based on the phlogiston theory, +in which, like Priestley, he always, believed. Although in error in +this respect, he was, nevertheless, able to make his discoveries with +extremely accurate interpretations. A brief epitome of the list of some +of his more important discoveries conveys some idea, of his fertility of +mind as well as his industry. In 1780 he discovered lactic acid,(7) and +showed that it was the substance that caused the acidity of sour +milk; and in the same year he discovered mucic acid. Next followed the +discovery of tungstic acid, and in 1783 he added to his list of useful +discoveries that of glycerine. Then in rapid succession came his +announcements of the new vegetable products citric, malic, oxalic, and +gallic acids. Scheele not only made the discoveries, but told the +world how he had made them--how any chemist might have made them if +he chose--for he never considered that he had really discovered any +substance until he had made it, decomposed it, and made it again. + +His experiments on Prussian blue are most interesting, not only because +of the enormous amount of work involved and the skill he displayed in +his experiments, but because all the time the chemist was handling, +smelling, and even tasting a compound of one of the most deadly poisons, +ignorant of the fact that the substance was a dangerous one to handle. +His escape from injury seems almost miraculous; for his experiments, +which were most elaborate, extended over a considerable period of time, +during which he seems to have handled this chemical with impunity. + +While only forty years of age and just at the zenith of his fame, +Scheele was stricken by a fatal illness, probably induced by his +ceaseless labor and exposure. It is gratifying to know, however, that +during the last eight or nine years of his life he had been less bound +down by pecuniary difficulties than before, as Bergman had obtained for +him an annual grant from the Academy. But it was characteristic of the +man that, while devoting one-sixth of the amount of this grant to his +personal wants, the remaining five-sixths was devoted to the expense of +his experiments. + + +LAVOISIER AND THE FOUNDATION OF MODERN CHEMISTRY + +The time was ripe for formulating the correct theory of chemical +composition: it needed but the master hand to mould the materials into +the proper shape. The discoveries in chemistry during the eighteenth +century had been far-reaching and revolutionary in character. A brief +review of these discoveries shows how completely they had subverted +the old ideas of chemical elements and chemical compounds. Of the four +substances earth, air, fire, and water, for many centuries believed +to be elementary bodies, not one has stood the test of the +eighteenth-century chemists. Earth had long since ceased to be regarded +as an element, and water and air had suffered the same fate in this +century. And now at last fire itself, the last of the four "elements" +and the keystone to the phlogiston arch, was shown to be nothing more +than one of the manifestations of the new element, oxygen, and not +"phlogiston" or any other intangible substance. + +In this epoch of chemical discoveries England had produced such mental +giants and pioneers in science as Black, Priestley, and Cavendish; +Sweden had given the world Scheele and Bergman, whose work, added to +that of their English confreres, had laid the broad base of chemistry +as a science; but it was for France to produce a man who gave the +final touches to the broad but rough workmanship of its foundation, +and establish it as the science of modern chemistry. It was for Antoine +Laurent Lavoisier (1743-1794) to gather together, interpret correctly, +rename, and classify the wealth of facts that his immediate predecessors +and contemporaries had given to the world. + +The attitude of the mother-countries towards these illustrious sons is +an interesting piece of history. Sweden honored and rewarded Scheele +and Bergman for their efforts; England received the intellectuality of +Cavendish with less appreciation than the Continent, and a fanatical mob +drove Priestley out of the country; while France, by sending Lavoisier +to the guillotine, demonstrated how dangerous it was, at that time +at least, for an intelligent Frenchman to serve his fellowman and his +country well. + +"The revolution brought about by Lavoisier in science," says Hoefer, +"coincides by a singular act of destiny with another revolution, much +greater indeed, going on then in the political and social world. Both +happened on the same soil, at the same epoch, among the same people; +and both marked the commencement of a new era in their respective +spheres."(8) + +Lavoisier was born in Paris, and being the son of an opulent family, +was educated under the instruction of the best teachers of the day. With +Lacaille he studied mathematics and astronomy; with Jussieu, botany; +and, finally, chemistry under Rouelle. His first work of importance was +a paper on the practical illumination of the streets of Paris, for which +a prize had been offered by M. de Sartine, the chief of police. This +prize was not awarded to Lavoisier, but his suggestions were of such +importance that the king directed that a gold medal be bestowed upon the +young author at the public sitting of the Academy in April, 1776. Two +years later, at the age of thirty-five, Lavoisier was admitted a member +of the Academy. + +In this same year he began to devote himself almost exclusively to +chemical inquiries, and established a laboratory in his home, fitted +with all manner of costly apparatus and chemicals. Here he was in +constant communication with the great men of science of Paris, to all of +whom his doors were thrown open. One of his first undertakings in this +laboratory was to demonstrate that water could not be converted into +earth by repeated distillations, as was generally advocated; and to show +also that there was no foundation to the existing belief that it was +possible to convert water into a gas so "elastic" as to pass through +the pores of a vessel. He demonstrated the fallaciousness of both these +theories in 1768-1769 by elaborate experiments, a single investigation +of this series occupying one hundred and one days. + +In 1771 he gave the first blow to the phlogiston theory by his +experiments on the calcination of metals. It will be recalled that one +basis for the belief in phlogiston was the fact that when a metal was +calcined it was converted into an ash, giving up its "phlogiston" in the +process. To restore the metal, it was necessary to add some substance +such as wheat or charcoal to the ash. Lavoisier, in examining this +process of restoration, found that there was always evolved a great +quantity of "air," which he supposed to be "fixed air" or carbonic +acid--the same that escapes in effervescence of alkalies and calcareous +earths, and in the fermentation of liquors. He then examined the process +of calcination, whereby the phlogiston of the metal was supposed to +have been drawn off. But far from finding that phlogiston or any other +substance had been driven off, he found that something had been taken +on: that the metal "absorbed air," and that the increased weight of the +metal corresponded to the amount of air "absorbed." Meanwhile he +was within grasp of two great discoveries, that of oxygen and of the +composition of the air, which Priestley made some two years later. + +The next important inquiry of this great Frenchman was as to the +composition of diamonds. With the great lens of Tschirnhausen belonging +to the Academy he succeeded in burning up several diamonds, regardless +of expense, which, thanks to his inheritance, he could ignore. In this +process he found that a gas was given off which precipitated lime from +water, and proved to be carbonic acid. Observing this, and experimenting +with other substances known to give off carbonic acid in the same +manner, he was evidently impressed with the now well-known fact that +diamond and charcoal are chemically the same. But if he did really +believe it, he was cautious in expressing his belief fully. "We should +never have expected," he says, "to find any relation between charcoal +and diamond, and it would be unreasonable to push this analogy too far; +it only exists because both substances seem to be properly ranged in the +class of combustible bodies, and because they are of all these bodies +the most fixed when kept from contact with air." + +As we have seen, Priestley, in 1774, had discovered oxygen, or +"dephlogisticated air." Four years later Lavoisier first advanced his +theory that this element discovered by Priestley was the universal +acidifying or oxygenating principle, which, when combined with charcoal +or carbon, formed carbonic acid; when combined with sulphur, formed +sulphuric (or vitriolic) acid; with nitrogen, formed nitric acid, +etc., and when combined with the metals formed oxides, or calcides. +Furthermore, he postulated the theory that combustion was not due to any +such illusive thing as "phlogiston," since this did not exist, and it +seemed to him that the phenomena of combustion heretofore attributed to +phlogiston could be explained by the action of the new element oxygen +and heat. This was the final blow to the phlogiston theory, which, +although it had been tottering for some time, had not been completely +overthrown. + +In 1787 Lavoisier, in conjunction with Guyon de Morveau, Berthollet, +and Fourcroy, introduced the reform in chemical nomenclature which until +then had remained practically unchanged since alchemical days. Such +expressions as "dephlogisticated" and "phlogisticated" would obviously +have little meaning to a generation who were no longer to believe in +the existence of phlogiston. It was appropriate that a revolution in +chemical thought should be accompanied by a corresponding revolution in +chemical names, and to Lavoisier belongs chiefly the credit of bringing +about this revolution. In his Elements of Chemistry he made use of this +new nomenclature, and it seemed so clearly an improvement over the +old that the scientific world hastened to adopt it. In this connection +Lavoisier says: "We have, therefore, laid aside the expression metallic +calx altogether, and have substituted in its place the word oxide. By +this it may be seen that the language we have adopted is both copious +and expressive. The first or lowest degree of oxygenation in bodies +converts them into oxides; a second degree of additional oxygenation +constitutes the class of acids of which the specific names drawn from +their particular bases terminate in ous, as in the nitrous and the +sulphurous acids. The third degree of oxygenation changes these into the +species of acids distinguished by the termination in ic, as the nitric +and sulphuric acids; and, lastly, we can express a fourth or higher +degree of oxygenation by adding the word oxygenated to the name of the +acid, as has already been done with oxygenated muriatic acid."(9) + +This new work when given to the world was not merely an epoch-making +book; it was revolutionary. It not only discarded phlogiston altogether, +but set forth that metals are simple elements, not compounds of "earth" +and "phlogiston." It upheld Cavendish's demonstration that water itself, +like air, is a compound of oxygen with another element. In short, it was +scientific chemistry, in the modern acceptance of the term. + +Lavoisier's observations on combustion are at once important and +interesting: "Combustion," he says, "... is the decomposition of oxygen +produced by a combustible body. The oxygen which forms the base of this +gas is absorbed by and enters into combination with the burning body, +while the caloric and light are set free. Every combustion necessarily +supposes oxygenation; whereas, on the contrary, every oxygenation +does not necessarily imply concomitant combustion; because combustion +properly so called cannot take place without disengagement of caloric +and light. Before combustion can take place, it is necessary that the +base of oxygen gas should have greater affinity to the combustible body +than it has to caloric; and this elective attraction, to use Bergman's +expression, can only take place at a certain degree of temperature which +is different for each combustible substance; hence the necessity of +giving the first motion or beginning to every combustion by the approach +of a heated body. This necessity of heating any body we mean to burn +depends upon certain considerations which have not hitherto been +attended to by any natural philosopher, for which reason I shall enlarge +a little upon the subject in this place: + +"Nature is at present in a state of equilibrium, which cannot have been +attained until all the spontaneous combustions or oxygenations possible +in an ordinary degree of temperature had taken place.... To illustrate +this abstract view of the matter by example: Let us suppose the usual +temperature of the earth a little changed, and it is raised only to the +degree of boiling water; it is evident that in this case phosphorus, +which is combustible in a considerably lower degree of temperature, +would no longer exist in nature in its pure and simple state, but would +always be procured in its acid or oxygenated state, and its radical +would become one of the substances unknown to chemistry. By gradually +increasing the temperature of the earth, the same circumstance would +successively happen to all the bodies capable of combustion; and, at +the last, every possible combustion having taken place, there would +no longer exist any combustible body whatever, and every substance +susceptible of the operation would be oxygenated and consequently +incombustible. + +"There cannot, therefore, exist, as far as relates to us, any +combustible body but such as are non-combustible at the ordinary +temperature of the earth, or, what is the same thing in other words, +that it is essential to the nature of every combustible body not to +possess the property of combustion unless heated, or raised to a degree +of temperature at which its combustion naturally takes place. When this +degree is once produced, combustion commences, and the caloric which +is disengaged by the decomposition of the oxygen gas keeps up the +temperature which is necessary for continuing combustion. When this is +not the case--that is, when the disengaged caloric is not sufficient +for keeping up the necessary temperature--the combustion ceases. This +circumstance is expressed in the common language by saying that a body +burns ill or with difficulty."(10) + + +It needed the genius of such a man as Lavoisier to complete the +refutation of the false but firmly grounded phlogiston theory, and +against such a book as his Elements of Chemistry the feeble weapons of +the supporters of the phlogiston theory were hurled in vain. + +But while chemists, as a class, had become converts to the new chemistry +before the end of the century, one man, Dr. Priestley, whose work had +done so much to found it, remained unconverted. In this, as in all his +life-work, he showed himself to be a most remarkable man. Davy said of +him, a generation later, that no other person ever discovered so many +new and curious substances as he; yet to the last he was only an amateur +in science, his profession, as we know, being the ministry. There is +hardly another case in history of a man not a specialist in science +accomplishing so much in original research as did this chemist, +physiologist, electrician; the mathematician, logician, and moralist; +the theologian, mental philosopher, and political economist. He took +all knowledge for his field; but how he found time for his numberless +researches and multifarious writings, along with his every-day duties, +must ever remain a mystery to ordinary mortals. + +That this marvellously receptive, flexible mind should have refused +acceptance to the clearly logical doctrines of the new chemistry seems +equally inexplicable. But so it was. To the very last, after all his +friends had capitulated, Priestley kept up the fight. From America he +sent out his last defy to the enemy, in 1800, in a brochure entitled +"The Doctrine of Phlogiston Upheld," etc. In the mind of its author it +was little less than a paean of victory; but all the world beside knew +that it was the swan-song of the doctrine of phlogiston. Despite the +defiance of this single warrior the battle was really lost and won, +and as the century closed "antiphlogistic" chemistry had practical +possession of the field. + + + + +III. CHEMISTRY SINCE THE TIME OF DALTON + +JOHN DALTON AND THE ATOMIC THEORY + +Small beginnings as have great endings--sometimes. As a case in +point, note what came of the small, original effort of a self-trained +back-country Quaker youth named John Dalton, who along towards the close +of the eighteenth century became interested in the weather, and was +led to construct and use a crude water-gauge to test the amount of the +rainfall. The simple experiments thus inaugurated led to no fewer than +two hundred thousand recorded observations regarding the weather, +which formed the basis for some of the most epochal discoveries in +meteorology, as we have seen. But this was only a beginning. The simple +rain-gauge pointed the way to the most important generalization of +the nineteenth century in a field of science with which, to the casual +observer, it might seem to have no alliance whatever. The wonderful +theory of atoms, on which the whole gigantic structure of modern +chemistry is founded, was the logical outgrowth, in the mind of John +Dalton, of those early studies in meteorology. + +The way it happened was this: From studying the rainfall, Dalton turned +naturally to the complementary process of evaporation. He was soon led +to believe that vapor exists, in the atmosphere as an independent gas. +But since two bodies cannot occupy the same space at the same time, +this implies that the various atmospheric gases are really composed of +discrete particles. These ultimate particles are so small that we cannot +see them--cannot, indeed, more than vaguely imagine them--yet each +particle of vapor, for example, is just as much a portion of water as if +it were a drop out of the ocean, or, for that matter, the ocean itself. +But, again, water is a compound substance, for it may be separated, as +Cavendish has shown, into the two elementary substances hydrogen and +oxygen. Hence the atom of water must be composed of two lesser atoms +joined together. Imagine an atom of hydrogen and one of oxygen. Unite +them, and we have an atom of water; sever them, and the water no longer +exists; but whether united or separate the atoms of hydrogen and of +oxygen remain hydrogen and oxygen and nothing else. Differently mixed +together or united, atoms produce different gross substances; but the +elementary atoms never change their chemical nature--their distinct +personality. + +It was about the year 1803 that Dalton first gained a full grasp of the +conception of the chemical atom. At once he saw that the hypothesis, +if true, furnished a marvellous key to secrets of matter hitherto +insoluble--questions relating to the relative proportions of the atoms +themselves. It is known, for example, that a certain bulk of hydrogen +gas unites with a certain bulk of oxygen gas to form water. If it be +true that this combination consists essentially of the union of atoms +one with another (each single atom of hydrogen united to a single atom +of oxygen), then the relative weights of the original masses of hydrogen +and of oxygen must be also the relative weights of each of their +respective atoms. If one pound of hydrogen unites with five and one-half +pounds of oxygen (as, according to Dalton's experiments, it did), then +the weight of the oxygen atom must be five and one-half times that of +the hydrogen atom. Other compounds may plainly be tested in the same +way. Dalton made numerous tests before he published his theory. He found +that hydrogen enters into compounds in smaller proportions than any +other element known to him, and so, for convenience, determined to take +the weight of the hydrogen atom as unity. The atomic weight of oxygen +then becomes (as given in Dalton's first table of 1803) 5.5; that of +water (hydrogen plus oxygen) being of course 6.5. The atomic weights of +about a score of substances are given in Dalton's first paper, which +was read before the Literary and Philosophical Society of Manchester, +October 21, 1803. I wonder if Dalton himself, great and acute intellect +though he had, suspected, when he read that paper, that he was +inaugurating one of the most fertile movements ever entered on in the +whole history of science? + +Be that as it may, it is certain enough that Dalton's contemporaries +were at first little impressed with the novel atomic theory. Just at +this time, as it chanced, a dispute was waging in the field of chemistry +regarding a matter of empirical fact which must necessarily be settled +before such a theory as that of Dalton could even hope for a bearing. +This was the question whether or not chemical elements unite with one +another always in definite proportions. Berthollet, the great co-worker +with Lavoisier, and now the most authoritative of living chemists, +contended that substances combine in almost indefinitely graded +proportions between fixed extremes. He held that solution is really a +form of chemical combination--a position which, if accepted, left no +room for argument. + +But this contention of the master was most actively disputed, in +particular by Louis Joseph Proust, and all chemists of repute were +obliged to take sides with one or the other. For a time the authority of +Berthollet held out against the facts, but at last accumulated evidence +told for Proust and his followers, and towards the close of the first +decade of our century it came to be generally conceded that chemical +elements combine with one another in fixed and definite proportions. + +More than that. As the analysts were led to weigh carefully the +quantities of combining elements, it was observed that the proportions +are not only definite, but that they bear a very curious relation to one +another. If element A combines with two different proportions of element +B to form two compounds, it appears that the weight of the larger +quantity of B is an exact multiple of that of the smaller quantity. This +curious relation was noticed by Dr. Wollaston, one of the most accurate +of observers, and a little later it was confirmed by Johan Jakob +Berzelius, the great Swedish chemist, who was to be a dominating +influence in the chemical world for a generation to come. But this +combination of elements in numerical proportions was exactly what Dalton +had noticed as early as 1802, and what bad led him directly to the +atomic weights. So the confirmation of this essential point by chemists +of such authority gave the strongest confirmation to the atomic theory. + +During these same years the rising authority of the French chemical +world, Joseph Louis Gay-Lussac, was conducting experiments with gases, +which he had undertaken at first in conjunction with Humboldt, but which +later on were conducted independently. In 1809, the next year after +the publication of the first volume of Dalton's New System of Chemical +Philosophy, Gay-Lussac published the results of his observations, and +among other things brought out the remarkable fact that gases, under +the same conditions as to temperature and pressure, combine always in +definite numerical proportions as to volume. Exactly two volumes of +hydrogen, for example, combine with one volume of oxygen to form water. +Moreover, the resulting compound gas always bears a simple relation to +the combining volumes. In the case just cited, the union of two volumes +of hydrogen and one of oxygen results in precisely two volumes of water +vapor. + +Naturally enough, the champions of the atomic theory seized upon +these observations of Gay-Lussac as lending strong support to their +hypothesis--all of them, that is, but the curiously self-reliant and +self-sufficient author of the atomic theory himself, who declined +to accept the observations of the French chemist as valid. Yet the +observations of Gay-Lussac were correct, as countless chemists since +then have demonstrated anew, and his theory of combination by volumes +became one of the foundation-stones of the atomic theory, despite the +opposition of the author of that theory. + +The true explanation of Gay-Lussac's law of combination by volumes was +thought out almost immediately by an Italian savant, Amadeo, Avogadro, +and expressed in terms of the atomic theory. The fact must be, said +Avogadro, that under similar physical conditions every form of gas +contains exactly the same number of ultimate particles in a given +volume. Each of these ultimate physical particles may be composed of two +or more atoms (as in the case of water vapor), but such a compound atom +conducts itself as if it were a simple and indivisible atom, as regards +the amount of space that separates it from its fellows under given +conditions of pressure and temperature. The compound atom, composed +of two or more elementary atoms, Avogadro proposed to distinguish, for +purposes of convenience, by the name molecule. It is to the molecule, +considered as the unit of physical structure, that Avogadro's law +applies. + +This vastly important distinction between atoms and molecules, implied +in the law just expressed, was published in 1811. Four years later, the +famous French physicist Ampere outlined a similar theory, and utilized +the law in his mathematical calculations. And with that the law of +Avogadro dropped out of sight for a full generation. Little suspecting +that it was the very key to the inner mysteries of the atoms for which +they were seeking, the chemists of the time cast it aside, and let it +fade from the memory of their science. + +This, however, was not strange, for of course the law of Avogadro is +based on the atomic theory, and in 1811 the atomic theory was itself +still being weighed in the balance. The law of multiple proportions +found general acceptance as an empirical fact; but many of the leading +lights of chemistry still looked askance at Dalton's explanation of this +law. Thus Wollaston, though from the first he inclined to acceptance of +the Daltonian view, cautiously suggested that it would be well to use +the non-committal word "equivalent" instead of "atom"; and Davy, for +a similar reason, in his book of 1812, speaks only of "proportions," +binding himself to no theory as to what might be the nature of these +proportions. + +At least two great chemists of the time, however, adopted the atomic +view with less reservation. One of these was Thomas Thomson, professor +at Edinburgh, who, in 1807, had given an outline of Dalton's theory in +a widely circulated book, which first brought the theory to the general +attention of the chemical world. The other and even more noted advocate +of the atomic theory was Johan Jakob Berzelius. This great Swedish +chemist at once set to work to put the atomic theory to such tests as +might be applied in the laboratory. He was an analyst of the utmost +skill, and for years he devoted himself to the determination of the +combining weights, "equivalents" or "proportions," of the different +elements. These determinations, in so far as they were accurately made, +were simple expressions of empirical facts, independent of any theory; +but gradually it became more and more plain that these facts all +harmonize with the atomic theory of Dalton. So by common consent the +proportionate combining weights of the elements came to be known as +atomic weights--the name Dalton had given them from the first--and +the tangible conception of the chemical atom as a body of definite +constitution and weight gained steadily in favor. + +From the outset the idea had had the utmost tangibility in the mind of +Dalton. He had all along represented the different atoms by geometrical +symbols--as a circle for oxygen, a circle enclosing a dot for hydrogen, +and the like--and had represented compounds by placing these symbols of +the elements in juxtaposition. Berzelius proposed to improve upon this +method by substituting for the geometrical symbol the initial of the +Latin name of the element represented--O for oxygen, H for hydrogen, and +so on--a numerical coefficient to follow the letter as an indication of +the number of atoms present in any given compound. This simple system +soon gained general acceptance, and with slight modifications it is +still universally employed. Every school-boy now is aware that H2O is +the chemical way of expressing the union of two atoms of hydrogen with +one of oxygen to form a molecule of water. But such a formula would have +had no meaning for the wisest chemist before the day of Berzelius. + +The universal fame of the great Swedish authority served to give general +currency to his symbols and atomic weights, and the new point of view +thus developed led presently to two important discoveries which removed +the last lingering doubts as to the validity of the atomic theory. In +1819 two French physicists, Dulong and Petit, while experimenting with +heat, discovered that the specific heats of solids (that is to say, the +amount of heat required to raise the temperature of a given mass to a +given degree) vary inversely as their atomic weights. In the same year +Eilhard Mitscherlich, a German investigator, observed that compounds +having the same number of atoms to the molecule are disposed to form the +same angles of crystallization--a property which he called isomorphism. + +Here, then, were two utterly novel and independent sets of empirical +facts which harmonize strangely with the supposition that substances are +composed of chemical atoms of a determinate weight. This surely could +not be coincidence--it tells of law. And so as soon as the claims of +Dulong and Petit and of Mitscherlich had been substantiated by other +observers, the laws of the specific heat of atoms, and of isomorphism, +took their place as new levers of chemical science. With the aid of +these new tools an impregnable breastwork of facts was soon piled about +the atomic theory. And John Dalton, the author of that theory, plain, +provincial Quaker, working on to the end in semi-retirement, became +known to all the world and for all time as a master of masters. + + +HUMPHRY DAVY AND ELECTRO-CHEMISTRY + +During those early years of the nineteenth century, when Dalton was +grinding away at chemical fact and theory in his obscure Manchester +laboratory, another Englishman held the attention of the chemical world +with a series of the most brilliant and widely heralded researches. This +was Humphry Davy, a young man who had conic to London in 1801, at the +instance of Count Rumford, to assume the chair of chemical philosophy in +the Royal Institution, which the famous American had just founded. + +Here, under Davy's direction, the largest voltaic battery yet +constructed had been put in operation, and with its aid the brilliant +young experimenter was expected almost to perform miracles. And indeed +he scarcely disappointed the expectation, for with the aid of his +battery he transformed so familiar a substance as common potash into +a metal which was not only so light that it floated on water, but +possessed the seemingly miraculous property of bursting into flames as +soon as it came in contact with that fire-quenching liquid. If this +were not a miracle, it had for the popular eye all the appearance of the +miraculous. + +What Davy really had done was to decompose the potash, which hitherto +had been supposed to be elementary, liberating its oxygen, and thus +isolating its metallic base, which he named potassium. The same +thing was done with soda, and the closely similar metal sodium was +discovered--metals of a unique type, possessed of a strange avidity for +oxygen, and capable of seizing on it even when it is bound up in the +molecules of water. Considered as mere curiosities, these discoveries +were interesting, but aside from that they were of great theoretical +importance, because they showed the compound nature of some familiar +chemicals that had been regarded as elements. Several other elementary +earths met the same fate when subjected to the electrical influence; the +metals barium, calcium, and strontium being thus discovered. Thereafter +Davy always referred to the supposed elementary substances (including +oxygen, hydrogen, and the rest) as "unde-compounded" bodies. These +resist all present efforts to decompose them, but how can one know what +might not happen were they subjected to an influence, perhaps some day +to be discovered, which exceeds the battery in power as the battery +exceeds the blowpipe? + +Another and even more important theoretical result that flowed from +Davy's experiments during this first decade of the century was the +proof that no elementary substances other than hydrogen and oxygen are +produced when pure water is decomposed by the electric current. It was +early noticed by Davy and others that when a strong current is passed +through water, alkalies appear at one pole of the battery and acids at +the other, and this though the water used were absolutely pure. This +seemingly told of the creation of elements--a transmutation but one step +removed from the creation of matter itself--under the influence of the +new "force." It was one of Davy's greatest triumphs to prove, in the +series of experiments recorded in his famous Bakerian lecture of 1806, +that the alleged creation of elements did not take place, the substances +found at the poles of the battery having been dissolved from the walls +of the vessels in which the water experimented upon had been placed. +Thus the same implement which had served to give a certain philosophical +warrant to the fading dreams of alchemy banished those dreams +peremptorily from the domain of present science. + +"As early as 1800," writes Davy, "I had found that when separate +portions of distilled water, filling two glass tubes, connected by moist +bladders, or any moist animal or vegetable substances, were submitted +to the electrical action of the pile of Volta by means of gold wires, +a nitro-muriatic solution of gold appeared in the tube containing the +positive wire, or the wire transmitting the electricity, and a solution +of soda in the opposite tube; but I soon ascertained that the muriatic +acid owed its existence to the animal or vegetable matters employed; +for when the same fibres of cotton were made use of in successive +experiments, and washed after every process in a weak solution of nitric +acid, the water in the apparatus containing them, though acted on for +a great length of time with a very strong power, at last produced no +effects upon nitrate of silver. + +"In cases when I had procured much soda, the glass at its point of +contact with the wire seemed considerably corroded; and I was confirmed +in my idea of referring the production of the alkali principally to +this source, by finding that no fixed saline matter could be obtained +by electrifying distilled water in a single agate cup from two points of +platina with the Voltaic battery. + +"Mr. Sylvester, however, in a paper published in Mr. Nicholson's journal +for last August, states that though no fixed alkali or muriatic acid +appears when a single vessel is employed, yet that they are both formed +when two vessels are used. And to do away with all objections with +regard to vegetable substances or glass, he conducted his process in +a vessel made of baked tobacco-pipe clay inserted in a crucible of +platina. I have no doubt of the correctness of his results; but the +conclusion appears objectionable. He conceives, that he obtained fixed +alkali, because the fluid after being heated and evaporated left a +matter that tinged turmeric brown, which would have happened had it +been lime, a substance that exists in considerable quantities in all +pipe-clay; and even allowing the presence of fixed alkali, the materials +employed for the manufacture of tobacco-pipes are not at all such as to +exclude the combinations of this substance. + +"I resumed the inquiry; I procured small cylindrical cups of agate of +the capacity of about one-quarter of a cubic inch each. They were +boiled for some hours in distilled water, and a piece of very white and +transparent amianthus that had been treated in the same way was made +then to connect together; they were filled with distilled water and +exposed by means of two platina wires to a current of electricity, from +one hundred and fifty pairs of plates of copper and zinc four inches +square, made active by means of solution of alum. After forty-eight +hours the process was examined: Paper tinged with litmus plunged into +the tube containing the transmitting or positive wire was immediately +strongly reddened. Paper colored by turmeric introduced into the other +tube had its color much deepened; the acid matter gave a very slight +degree of turgidness to solution of nitrate of soda. The fluid that +affected turmeric retained this property after being strongly +boiled; and it appeared more vivid as the quantity became reduced by +evaporation; carbonate of ammonia was mixed with it, and the whole +dried and exposed to a strong heat; a minute quantity of white matter +remained, which, as far as my examinations could go, had the properties +of carbonate of soda. I compared it with similar minute portions of +the pure carbonates of potash, and similar minute portions of the pure +carbonates of potash and soda. It was not so deliquescent as the former +of these bodies, and it formed a salt with nitric acid, which, like +nitrate of soda, soon attracted moisture from a damp atmosphere and +became fluid. + +"This result was unexpected, but it was far from convincing me that the +substances which were obtained were generated. In a similar process with +glass tubes, carried on under exactly the same circumstances and for +the same time, I obtained a quantity of alkali which must have been more +than twenty times greater, but no traces of muriatic acid. There was +much probability that the agate contained some minute portion of saline +matter, not easily detected by chemical analysis, either in combination +or intimate cohesion in its pores. To determine this, I repeated this a +second, a third, and a fourth time. In the second experiment turbidness +was still produced by a solution of nitrate of silver in the tube +containing the acid, but it was less distinct; in the third process +it was barely perceptible; and in the fourth process the two fluids +remained perfectly clear after the mixture. The quantity of alkaline +matter diminished in every operation; and in the last process, though +the battery had been kept in great activity for three days, the fluid +possessed, in a very slight degree, only the power of acting on paper +tinged with turmeric; but its alkaline property was very sensible to +litmus paper slightly reddened, which is a much more delicate test; +and after evaporation and the process by carbonate of ammonia, a barely +perceptible quantity of fixed alkali was still left. The acid matter in +the other tube was abundant; its taste was sour; it smelled like water +over which large quantities of nitrous gas have been long kept; it did +not effect solution of muriate of barytes; and a drop of it placed +upon a polished plate of silver left, after evaporation, a black stain, +precisely similar to that produced by extremely diluted nitrous acid. + +"After these results I could no longer doubt that some saline matter +existing in the agate tubes had been the source of the acid matter +capable of precipitating nitrate of silver and much of the alkali. Four +additional repetitions of the process, however, convinced me that there +was likewise some other cause for the presence of this last substance; +for it continued to appear to the last in quantities sufficiently +distinguishable, and apparently equal in every case. I had used every +precaution, I had included the tube in glass vessels out of the reach of +the circulating air; all the acting materials had been repeatedly washed +with distilled water; and no part of them in contact with the fluid had +been touched by the fingers. + +"The only substance that I could now conceive as furnishing the fixed +alkali was the water itself. This water appeared pure by the tests of +nitrate of silver and muriate of barytes; but potash of soda, as is +well known, rises in small quantities in rapid distillation; and the +New River water which I made use of contains animal and vegetable +impurities, which it was easy to conceive might furnish neutral +salts capable of being carried over in vivid ebullition."(1) Further +experiment proved the correctness of this inference, and the last doubt +as to the origin of the puzzling chemical was dispelled. + +Though the presence of the alkalies and acids in the water was +explained, however, their respective migrations to the negative and +positive poles of the battery remained to be accounted for. Davy's +classical explanation assumed that different elements differ among +themselves as to their electrical properties, some being positively, +others negatively, electrified. Electricity and "chemical affinity," he +said, apparently are manifestations of the same force, acting in the one +case on masses, in the other on particles. Electro-positive particles +unite with electro-negative particles to form chemical compounds, in +virtue of the familiar principle that opposite electricities attract +one another. When compounds are decomposed by the battery, this mutual +attraction is overcome by the stronger attraction of the poles of the +battery itself. + +This theory of binary composition of all chemical compounds, through the +union of electro-positive and electro-negative atoms or molecules, +was extended by Berzelius, and made the basis of his famous system of +theoretical chemistry. This theory held that all inorganic compounds, +however complex their composition, are essentially composed of such +binary combinations. For many years this view enjoyed almost undisputed +sway. It received what seemed strong confirmation when Faraday showed +the definite connection between the amount of electricity employed and +the amount of decomposition produced in the so-called electrolyte. But +its claims were really much too comprehensive, as subsequent discoveries +proved. + + +ORGANIC CHEMISTRY AND THE IDEA OF THE MOLECULE + +When Berzelius first promulgated his binary theory he was careful to +restrict its unmodified application to the compounds of the inorganic +world. At that time, and for a long time thereafter, it was supposed +that substances of organic nature had some properties that kept them +aloof from the domain of inorganic chemistry. It was little doubted +that a so-called "vital force" operated here, replacing or modifying the +action of ordinary "chemical affinity." It was, indeed, admitted that +organic compounds are composed of familiar elements--chiefly carbon, +oxygen, hydrogen, and nitrogen; but these elements were supposed to +be united in ways that could not be imitated in the domain of the +non-living. It was regarded almost as an axiom of chemistry that +no organic compound whatever could be put together from its +elements--synthesized--in the laboratory. To effect the synthesis of +even the simplest organic compound, it was thought that the "vital +force" must be in operation. + +Therefore a veritable sensation was created in the chemical world +when, in the year 1828, it was announced that the young German chemist, +Friedrich Wohler, formerly pupil of Berzelius, and already known as a +coming master, had actually synthesized the well-known organic product +urea in his laboratory at Sacrow. The "exception which proves the rule" +is something never heard of in the domain of logical science. Natural +law knows no exceptions. So the synthesis of a single organic compound +sufficed at a blow to break down the chemical barrier which the +imagination of the fathers of the science had erected between animate +and inanimate nature. Thenceforth the philosophical chemist would +regard the plant and animal organisms as chemical laboratories in which +conditions are peculiarly favorable for building up complex compounds of +a few familiar elements, under the operation of universal chemical laws. +The chimera "vital force" could no longer gain recognition in the domain +of chemistry. + +Now a wave of interest in organic chemistry swept over the chemical +world, and soon the study of carbon compounds became as much the fashion +as electrochemistry had been in the, preceding generation. + +Foremost among the workers who rendered this epoch of organic chemistry +memorable were Justus Liebig in Germany and Jean Baptiste Andre Dumas +in France, and their respective pupils, Charles Frederic Gerhardt and +Augustus Laurent. Wohler, too, must be named in the same breath, as also +must Louis Pasteur, who, though somewhat younger than the others, came +upon the scene in time to take chief part in the most important of the +controversies that grew out of their labors. + +Several years earlier than this the way had been paved for the study +of organic substances by Gay-Lussac's discovery, made in 1815, that a +certain compound of carbon and nitrogen, which he named cyanogen, has a +peculiar degree of stability which enables it to retain its identity and +enter into chemical relations after the manner of a simple body. A year +later Ampere discovered that nitrogen and hydrogen, when combined in +certain proportions to form what he called ammonium, have the same +property. Berzelius had seized upon this discovery of the compound +radical, as it was called, because it seemed to lend aid to his +dualistic theory. He conceived the idea that all organic compounds +are binary unions of various compound radicals with an atom of oxygen, +announcing this theory in 1818. Ten years later, Liebig and Wohler +undertook a joint investigation which resulted in proving that compound +radicals are indeed very abundant among organic substances. Thus the +theory of Berzelius seemed to be substantiated, and organic chemistry +came to be defined as the chemistry of compound radicals. + +But even in the day of its seeming triumph the dualistic theory +was destined to receive a rude shock. This came about through the +investigations of Dumas, who proved that in a certain organic substance +an atom of hydrogen may be removed and an atom of chlorine substituted +in its place without destroying the integrity of the original +compound--much as a child might substitute one block for another in +its play-house. Such a substitution would be quite consistent with the +dualistic theory, were it not for the very essential fact that hydrogen +is a powerfully electro-positive element, while chlorine is as strongly +electro-negative. Hence the compound radical which united successively +with these two elements must itself be at one time electro-positive, at +another electro-negative--a seeming inconsistency which threw the entire +Berzelian theory into disfavor. + +In its place there was elaborated, chiefly through the efforts of +Laurent and Gerhardt, a conception of the molecule as a unitary +structure, built up through the aggregation of various atoms, in +accordance with "elective affinities" whose nature is not yet understood +A doctrine of "nuclei" and a doctrine of "types" of molecular structure +were much exploited, and, like the doctrine of compound radicals, became +useful as aids to memory and guides for the analyst, indicating some of +the plans of molecular construction, though by no means penetrating the +mysteries of chemical affinity. They are classifications rather than +explanations of chemical unions. But at least they served an important +purpose in giving definiteness to the idea of a molecular structure +built of atoms as the basis of all substances. Now at last the word +molecule came to have a distinct meaning, as distinct from "atom," in +the minds of the generality of chemists, as it had had for Avogadro a +third of a century before. Avogadro's hypothesis that there are equal +numbers of these molecules in equal volumes of gases, under fixed +conditions, was revived by Gerhardt, and a little later, under the +championship of Cannizzaro, was exalted to the plane of a fixed law. +Thenceforth the conception of the molecule was to be as dominant a +thought in chemistry as the idea of the atom had become in a previous +epoch. + + +CHEMICAL AFFINITY + +Of course the atom itself was in no sense displaced, but Avogadro's law +soon made it plain that the atom had often usurped territory that +did not really belong to it. In many cases the chemists had supposed +themselves dealing with atoms as units where the true unit was the +molecule. In the case of elementary gases, such as hydrogen and oxygen, +for example, the law of equal numbers of molecules in equal spaces made +it clear that the atoms do not exist isolated, as had been supposed. +Since two volumes of hydrogen unite with one volume of oxygen to form +two volumes of water vapor, the simplest mathematics show, in the light +of Avogadro's law, not only that each molecule of water must contain two +hydrogen atoms (a point previously in dispute), but that the original +molecules of hydrogen and oxygen must have been composed in each case of +two atoms---else how could one volume of oxygen supply an atom for every +molecule of two volumes of water? + +What, then, does this imply? Why, that the elementary atom has +an avidity for other atoms, a longing for companionship, an +"affinity"--call it what you will--which is bound to be satisfied if +other atoms are in the neighborhood. Placed solely among atoms of its +own kind, the oxygen atom seizes on a fellow oxygen atom, and in all +their mad dancings these two mates cling together--possibly revolving +about each other in miniature planetary orbits. Precisely the same thing +occurs among the hydrogen atoms. But now suppose the various pairs +of oxygen atoms come near other pairs of hydrogen atoms (under proper +conditions which need not detain us here), then each oxygen atom loses +its attachment for its fellow, and flings itself madly into the circuit +of one of the hydrogen couplets, and--presto!--there are only two +molecules for every three there were before, and free oxygen and +hydrogen have become water. The whole process, stated in chemical +phraseology, is summed up in the statement that under the given +conditions the oxygen atoms had a greater affinity for the hydrogen +atoms than for one another. + +As chemists studied the actions of various kinds of atoms, in regard +to their unions with one another to form molecules, it gradually dawned +upon them that not all elements are satisfied with the same number of +companions. Some elements ask only one, and refuse to take more; while +others link themselves, when occasion offers, with two, three, four, or +more. Thus we saw that oxygen forsook a single atom of its own kind +and linked itself with two atoms of hydrogen. Clearly, then, the oxygen +atom, like a creature with two hands, is able to clutch two other atoms. +But we have no proof that under any circumstances it could hold more +than two. Its affinities seem satisfied when it has two bonds. But, +on the other hand, the atom of nitrogen is able to hold three atoms +of hydrogen, and does so in the molecule of ammonium (NH3); while the +carbon atom can hold four atoms of hydrogen or two atoms of oxygen. + +Evidently, then, one atom is not always equivalent to another atom of +a different kind in combining powers. A recognition of this fact by +Frankland about 1852, and its further investigation by others (notably +A. Kekule and A. S. Couper), led to the introduction of the word +equivalent into chemical terminology in a new sense, and in particular +to an understanding of the affinities or "valency" of different +elements, which proved of the most fundamental importance. Thus it +was shown that, of the four elements that enter most prominently into +organic compounds, hydrogen can link itself with only a single bond to +any other element--it has, so to speak, but a single hand with which +to grasp--while oxygen has capacity for two bonds, nitrogen for +three (possibly for five), and carbon for four. The words monovalent, +divalent, trivalent, tretrava-lent, etc., were coined to express this +most important fact, and the various elements came to be known as +monads, diads, triads, etc. Just why different elements should differ +thus in valency no one as yet knows; it is an empirical fact that they +do. And once the nature of any element has been determined as regards +its valency, a most important insight into the possible behavior of that +element has been secured. Thus a consideration of the fact that hydrogen +is monovalent, while oxygen is divalent, makes it plain that we +must expect to find no more than three compounds of these two +elements--namely, H--O--(written HO by the chemist, and called +hydroxyl); H--O--H (H2O, or water), and H--O--O--H (H2O2, or hydrogen +peroxide). It will be observed that in the first of these compounds the +atom of oxygen stands, so to speak, with one of its hands free, eagerly +reaching out, therefore, for another companion, and hence, in the +language of chemistry, forming an unstable compound. Again, in the third +compound, though all hands are clasped, yet one pair links oxygen with +oxygen; and this also must be an unstable union, since the avidity of an +atom for its own kind is relatively weak. Thus the well-known properties +of hydrogen peroxide are explained, its easy decomposition, and the +eagerness with which it seizes upon the elements of other compounds. + +But the molecule of water, on the other hand, has its atoms arranged +in a state of stable equilibrium, all their affinities being satisfied. +Each hydrogen atom has satisfied its own affinity by clutching the +oxygen atom; and the oxygen atom has both its bonds satisfied by +clutching back at the two hydrogen atoms. Therefore the trio, linked in +this close bond, have no tendency to reach out for any other companion, +nor, indeed, any power to hold another should it thrust itself +upon them. They form a "stable" compound, which under all ordinary +circumstances will retain its identity as a molecule of water, even +though the physical mass of which it is a part changes its condition +from a solid to a gas from ice to vapor. + +But a consideration of this condition of stable equilibrium in the +molecule at once suggests a new question: How can an aggregation of +atoms, having all their affinities satisfied, take any further part in +chemical reactions? Seemingly such a molecule, whatever its physical +properties, must be chemically inert, incapable of any atomic +readjustments. And so in point of fact it is, so long as its component +atoms cling to one another unremittingly. But this, it appears, is +precisely what the atoms are little prone to do. It seems that they are +fickle to the last degree in their individual attachments, and are as +prone to break away from bondage as they are to enter into it. Thus the +oxygen atom which has just flung itself into the circuit of two +hydrogen atoms, the next moment flings itself free again and seeks +new companions. It is for all the world like the incessant change +of partners in a rollicking dance. This incessant dissolution and +reformation of molecules in a substance which as a whole remains +apparently unchanged was first fully appreciated by Ste.-Claire Deville, +and by him named dissociation. It is a process which goes on much more +actively in some compounds than in others, and very much more actively +under some physical conditions (such as increase of temperature) than +under others. But apparently no substances at ordinary temperatures, +and no temperature above the absolute zero, are absolutely free from its +disturbing influence. Hence it is that molecules having all the +valency of their atoms fully satisfied do not lose their chemical +activity--since each atom is momentarily free in the exchange of +partners, and may seize upon different atoms from its former partners, +if those it prefers are at hand. + +While, however, an appreciation of this ceaseless activity of the atom +is essential to a proper understanding of its chemical efficiency, +yet from another point of view the "saturated" molecule--that is, the +molecule whose atoms have their valency all satisfied--may be thought of +as a relatively fixed or stable organism. Even though it may presently +be torn down, it is for the time being a completed structure; and a +consideration of the valency of its atoms gives the best clew that has +hitherto been obtainable as to the character of its architecture. +How important this matter of architecture of the molecule--of space +relations of the atoms--may be--was demonstrated as long ago as 1823, +when Liebig and Wohler proved, to the utter bewilderment of the +chemical world, that two substances may have precisely the same chemical +constitution--the same number and kind of atoms--and yet differ utterly +in physical properties. The word isomerism was coined by Berzelius to +express this anomalous condition of things, which seemed to negative the +most fundamental truths of chemistry. Naming the condition by no means +explained it, but the fact was made clear that something besides the +mere number and kind of atoms is important in the architecture of a +molecule. It became certain that atoms are not thrown together haphazard +to build a molecule, any more than bricks are thrown together at random +to form a house. + +How delicate may be the gradations of architectural design in building +a molecule was well illustrated about 1850, when Pasteur discovered that +some carbon compounds--as certain sugars--can only be distinguished +from one another, when in solution, by the fact of their twisting or +polarizing a ray of light to the left or to the right, respectively. But +no inkling of an explanation of these strange variations of molecular +structure came until the discovery of the law of valency. Then much of +the mystery was cleared away; for it was plain that since each atom in a +molecule can hold to itself only a fixed number of other atoms, complex +molecules must have their atoms linked in definite chains or groups. And +it is equally plain that where the atoms are numerous, the exact plan of +grouping may sometimes be susceptible of change without doing violence +to the law of valency. It is in such cases that isomerism is observed to +occur. + +By paying constant heed to this matter of the affinities, chemists are +able to make diagrammatic pictures of the plan of architecture of any +molecule whose composition is known. In the simple molecule of water +(H2O), for example, the two hydrogen atoms must have released each +other before they could join the oxygen, and the manner of linking must +apparently be that represented in the graphic formula H--O--H. +With molecules composed of a large number of atoms, such graphic +representation of the scheme of linking is of course increasingly +difficult, yet, with the affinities for a guide, it is always possible. +Of course no one supposes that such a formula, written in a single +plane, can possibly represent the true architecture of the molecule: +it is at best suggestive or diagrammatic rather than pictorial. +Nevertheless, it affords hints as to the structure of the molecule such +as the fathers of chemistry would not have thought it possible ever to +attain. + + +PERIODICITY OF ATOMIC WEIGHTS + +These utterly novel studies of molecular architecture may seem at +first sight to take from the atom much of its former prestige as the +all-important personage of the chemical world. Since so much depends +upon the mere position of the atoms, it may appear that comparatively +little depends upon the nature of the atoms themselves. But such a view +is incorrect, for on closer consideration it will appear that at no +time has the atom been seen to renounce its peculiar personality. Within +certain limits the character of a molecule may be altered by changing +the positions of its atoms (just as different buildings may be +constructed of the same bricks), but these limits are sharply defined, +and it would be as impossible to exceed them as it would be to build +a stone building with bricks. From first to last the brick remains a +brick, whatever the style of architecture it helps to construct; it +never becomes a stone. And just as closely does each atom retain its own +peculiar properties, regardless of its surroundings. + +Thus, for example, the carbon atom may take part in the formation at one +time of a diamond, again of a piece of coal, and yet again of a +particle of sugar, of wood fibre, of animal tissue, or of a gas in the +atmosphere; but from first to last--from glass-cutting gem to intangible +gas--there is no demonstrable change whatever in any single property of +the atom itself. So far as we know, its size, its weight, its capacity +for vibration or rotation, and its inherent affinities, remain +absolutely unchanged throughout all these varying fortunes of position +and association. And the same thing is true of every atom of all of +the seventy-odd elementary substances with which the modern chemist is +acquainted. Every one appears always to maintain its unique integrity, +gaining nothing and losing nothing. + +All this being true, it would seem as if the position of the Daltonian +atom as a primordial bit of matter, indestructible and non-transmutable, +had been put to the test by the chemistry of our century, and not found +wanting. Since those early days of the century when the electric battery +performed its miracles and seemingly reached its limitations in the +hands of Davy, many new elementary substances have been discovered, +but no single element has been displaced from its position as an +undecomposable body. Rather have the analyses of the chemist seemed to +make it more and more certain that all elementary atoms are in truth +what John Herschel called them, "manufactured articles"--primordial, +changeless, indestructible. + +And yet, oddly enough, it has chanced that hand in hand with the +experiments leading to such a goal have gone other experiments arid +speculations of exactly the opposite tenor. In each generation there +have been chemists among the leaders of their science who have refused +to admit that the so-called elements are really elements at all in any +final sense, and who have sought eagerly for proof which might warrant +their scepticism. The first bit of evidence tending to support this view +was furnished by an English physician, Dr. William Prout, who in 1815 +called attention to a curious relation to be observed between the atomic +weight of the various elements. Accepting the figures given by the +authorities of the time (notably Thomson and Berzelius), it appeared +that a strikingly large proportion of the atomic weights were exact +multiples of the weight of hydrogen, and that others differed so +slightly that errors of observation might explain the discrepancy. Prout +felt that it could not be accidental, and he could think of no tenable +explanation, unless it be that the atoms of the various alleged elements +are made up of different fixed numbers of hydrogen atoms. Could it be +that the one true element--the one primal matter--is hydrogen, and that +all other forms of matter are but compounds of this original substance? + +Prout advanced this startling idea at first tentatively, in an anonymous +publication; but afterwards he espoused it openly and urged its +tenability. Coming just after Davy's dissociation of some supposed +elements, the idea proved alluring, and for a time gained such +popularity that chemists were disposed to round out the observed atomic +weights of all elements into whole numbers. But presently renewed +determinations of the atomic weights seemed to discountenance this +practice, and Prout's alleged law fell into disrepute. It was revived, +however, about 1840, by Dumas, whose great authority secured it a +respectful hearing, and whose careful redetermination of the weight +of carbon, making it exactly twelve times that of hydrogen, aided the +cause. + +Subsequently Stas, the pupil of Dumas, undertook a long series of +determinations of atomic weights, with the expectation of confirming the +Proutian hypothesis. But his results seemed to disprove the hypothesis, +for the atomic weights of many elements differed from whole numbers by +more, it was thought, than the limits of error of the experiments. It +was noteworthy, however, that the confidence of Dumas was not shaken, +though he was led to modify the hypothesis, and, in accordance with +previous suggestions of Clark and of Marignac, to recognize as the +primordial element, not hydrogen itself, but an atom half the weight, +or even one-fourth the weight, of that of hydrogen, of which primordial +atom the hydrogen atom itself is compounded. But even in this modified +form the hypothesis found great opposition from experimental observers. + +In 1864, however, a novel relation between the weights of the elements +and their other characteristics was called to the attention of chemists +by Professor John A. R. Newlands, of London, who had noticed that if the +elements are arranged serially in the numerical order of their atomic +weights, there is a curious recurrence of similar properties at +intervals of eight elements This so-called "law of octaves" attracted +little immediate attention, but the facts it connotes soon came under +the observation of other chemists, notably of Professors Gustav Hinrichs +in America, Dmitri Mendeleeff in Russia, and Lothar Meyer in Germany. +Mendeleeff gave the discovery fullest expression, explicating it in +1869, under the title of "the periodic law." + +Though this early exposition of what has since been admitted to be a +most important discovery was very fully outlined, the generality of +chemists gave it little heed till a decade or so later, when three new +elements, gallium, scandium, and germanium, were discovered, which, on +being analyzed, were quite unexpectedly found to fit into three gaps +which Mendeleeff had left in his periodic scale. In effect the periodic +law had enabled Mendeleeff to predicate the existence of the new +elements years before they were discovered. Surely a system that leads +to such results is no mere vagary. So very soon the periodic law took +its place as one of the most important generalizations of chemical +science. + +This law of periodicity was put forward as an expression of observed +relations independent of hypothesis; but of course the theoretical +bearings of these facts could not be overlooked. As Professor J. H. +Gladstone has said, it forces upon us "the conviction that the elements +are not separate bodies created without reference to one another, but +that they have been originally fashioned, or have been built up, from +one another, according to some general plan." It is but a short step +from that proposition to the Proutian hypothesis. + + +NEW WEAPONS--SPECTROSCOPE AND CAMERA + +But the atomic weights are not alone in suggesting the compound nature +of the alleged elements. Evidence of a totally different kind has +contributed to the same end, from a source that could hardly have been +imagined when the Proutian hypothesis, was formulated, through the +tradition of a novel weapon to the armamentarium of the chemist--the +spectroscope. The perfection of this instrument, in the hands of two +German scientists, Gustav Robert Kirchhoff and Robert Wilhelm Bunsen, +came about through the investigation, towards the middle of the century, +of the meaning of the dark lines which had been observed in the solar +spectrum by Fraunhofer as early as 1815, and by Wollaston a decade +earlier. It was suspected by Stokes and by Fox Talbot in England, but +first brought to demonstration by Kirchhoff and Bunsen, that these +lines, which were known to occupy definite positions in the spectrum, +are really indicative of particular elementary substances. By means of +the spectroscope, which is essentially a magnifying lens attached to a +prism of glass, it is possible to locate the lines with great accuracy, +and it was soon shown that here was a new means of chemical analysis +of the most exquisite delicacy. It was found, for example, that the +spectroscope could detect the presence of a quantity of sodium so +infinitesimal as the one two-hundred-thousandth of a grain. But what was +even more important, the spectroscope put no limit upon the distance of +location of the substance it tested, provided only that sufficient light +came from it. The experiments it recorded might be performed in the sun, +or in the most distant stars or nebulae; indeed, one of the earliest +feats of the instrument was to wrench from the sun the secret of his +chemical constitution. + +To render the utility of the spectroscope complete, however, it +was necessary to link with it another new chemical agency--namely, +photography. This now familiar process is based on the property of light +to decompose certain unstable compounds of silver, and thus alter their +chemical composition. Davy and Wedgwood barely escaped the discovery of +the value of the photographic method early in the nineteenth century. +Their successors quite overlooked it until about 1826, when Louis J. M. +Daguerre, the French chemist, took the matter in hand, and after many +years of experimentation brought it to relative perfection in 1839, in +which year the famous daguerreotype first brought the matter to popular +attention. In the same year Mr. Fox Talbot read a paper on the subject +before the Royal Society, and soon afterwards the efforts of Herschel +and numerous other natural philosophers contributed to the advancement +of the new method. + +In 1843 Dr. John W. Draper, the famous English-American chemist and +physiologist, showed that by photography the Fraunhofer lines in the +solar spectrum might be mapped with absolute accuracy; also proving that +the silvered film revealed many lines invisible to the unaided eye. The +value of this method of observation was recognized at once, and, as +soon as the spectroscope was perfected, the photographic method, in +conjunction with its use, became invaluable to the chemist. By this +means comparisons of spectra may be made with a degree of accuracy +not otherwise obtainable; and, in case of the stars, whole clusters of +spectra may be placed on record at a single observation. + +As the examination of the sun and stars proceeded, chemists were amazed +or delighted, according to their various preconceptions, to witness the +proof that many familiar terrestrial elements are to be found in the +celestial bodies. But what perhaps surprised them most was to observe +the enormous preponderance in the sidereal bodies of the element +hydrogen. Not only are there vast quantities of this element in the +sun's atmosphere, but some other suns appeared to show hydrogen lines +almost exclusively in their spectra. Presently it appeared that the +stars of which this is true are those white stars, such as Sirius, which +had been conjectured to be the hottest; whereas stars that are only +red-hot, like our sun, show also the vapors of many other elements, +including iron and other metals. + +In 1878 Professor J. Norman Lockyer, in a paper before the Royal +Society, called attention to the possible significance of this series of +observations. He urged that the fact of the sun showing fewer elements +than are observed here on the cool earth, while stars much hotter than +the sun show chiefly one element, and that one hydrogen, the lightest of +known elements, seemed to give color to the possibility that our alleged +elements are really compounds, which at the temperature of the hottest +stars may be decomposed into hydrogen, the latter "element" itself being +also doubtless a compound, which might be resolved under yet more trying +conditions. + +Here, then, was what might be termed direct experimental evidence for +the hypothesis of Prout. Unfortunately, however, it is evidence of a +kind which only a few experts are competent to discuss--so very delicate +a matter is the spectral analysis of the stars. What is still more +unfortunate, the experts do not agree among themselves as to the +validity of Professor Lockyer's conclusions. Some, like Professor +Crookes, have accepted them with acclaim, hailing Lockyer as "the +Darwin of the inorganic world," while others have sought a different +explanation of the facts he brings forward. As yet it cannot be said +that the controversy has been brought to final settlement. Still, it is +hardly to be doubted that now, since the periodic law has seemed to +join hands with the spectroscope, a belief in the compound nature of the +so-called elements is rapidly gaining ground among chemists. More and +more general becomes the belief that the Daltonian atom is really a +compound radical, and that back of the seeming diversity of the alleged +elements is a single form of primordial matter. Indeed, in very recent +months, direct experimental evidence for this view has at last come to +hand, through the study of radio-active substances. In a later chapter +we shall have occasion to inquire how this came about. + + + + +IV. ANATOMY AND PHYSIOLOGY IN THE EIGHTEENTH CENTURY + +ALBRECHT VON HALLER + +An epoch in physiology was made in the eighteenth century by the genius +and efforts of Albrecht von Haller (1708-1777), of Berne, who is perhaps +as worthy of the title "The Great" as any philosopher who has been +so christened by his contemporaries since the time of Hippocrates. +Celebrated as a physician, he was proficient in various fields, being +equally famed in his own time as poet, botanist, and statesman, and +dividing his attention between art and science. + +As a child Haller was so sickly that he was unable to amuse himself with +the sports and games common to boys of his age, and so passed most of +his time poring over books. When ten years of age he began writing poems +in Latin and German, and at fifteen entered the University of Tubingen. +At seventeen he wrote learned articles in opposition to certain accepted +doctrines, and at nineteen he received his degree of doctor. Soon after +this he visited England, where his zeal in dissecting brought him under +suspicion of grave-robbery, which suspicion made it expedient for him to +return to the Continent. After studying botany in Basel for some time he +made an extended botanical journey through Switzerland, finally settling +in his native city, Berne, as a practising physician. During this time +he did not neglect either poetry or botany, publishing anonymously a +collection of poems. + +In 1736 he was called to Gottingen as professor of anatomy, surgery, +chemistry, and botany. During his labors in the university he never +neglected his literary work, sometimes living and sleeping for days and +nights together in his library, eating his meals while delving in his +books, and sleeping only when actually compelled to do so by fatigue. +During all this time he was in correspondence with savants from all over +the world, and it is said of him that he never left a letter of any kind +unanswered. + +Haller's greatest contribution to medical science was his famous +doctrine of irritability, which has given him the name of "father of +modern nervous physiology," just as Harvey is called "the father of +the modern physiology of the blood." It has been said of this +famous doctrine of irritability that "it moved all the minds of the +century--and not in the departments of medicine alone--in a way of which +we of the present day have no satisfactory conception, unless we compare +it with our modern Darwinism."(1) + +The principle of general irritability had been laid down by Francis +Glisson (1597-1677) from deductive studies, but Haller proved by +experiments along the line of inductive methods that this irritability +was not common to all "fibre as well as to the fluids of the body," but +something entirely special, and peculiar only to muscular substance. He +distinguished between irritability of muscles and sensibility of nerves. +In 1747 he gave as the three forces that produce muscular movements: +elasticity, or "dead nervous force"; irritability, or "innate nervous +force"; and nervous force in itself. And in 1752 he described one +hundred and ninety experiments for determining what parts of the body +possess "irritability"--that is, the property of contracting when +stimulated. His conclusion that this irritability exists in muscular +substance alone and is quite independent of the nerves proceeding to it +aroused a controversy that was never definitely settled until late in +the nineteenth century, when Haller's theory was found to be entirely +correct. + +It was in pursuit of experiments to establish his theory of irritability +that Haller made his chief discoveries in embryology and development. He +proved that in the process of incubation of the egg the first trace of +the heart of the chick shows itself in the thirty-eighth hour, and that +the first trace of red blood showed in the forty-first hour. By his +investigations upon the lower animals he attempted to confirm the theory +that since the creation of genus every individual is derived from a +preceding individual--the existing theory of preformation, in which +he believed, and which taught that "every individual is fully and +completely preformed in the germ, simply growing from microscopic to +visible proportions, without developing any new parts." + +In physiology, besides his studies of the nervous system, Haller studied +the mechanism of respiration, refuting the teachings of Hamberger +(1697-1755), who maintained that the lungs contract independently. +Haller, however, in common with his contemporaries, failed utterly to +understand the true function of the lungs. The great physiologist's +influence upon practical medicine, while most profound, was largely +indirect. He was a theoretical rather than a practical physician, yet he +is credited with being the first physician to use the watch in counting +the pulse. + + +BATTISTA MORGAGNI AND MORBID ANATOMY + +A great contemporary of Haller was Giovanni Battista Morgagni +(1682-1771), who pursued what Sydenham had neglected, the investigation +in anatomy, thus supplying a necessary counterpart to the great +Englishman's work. Morgagni's investigations were directed chiefly to +the study of morbid anatomy--the study of the structure of diseased +tissue, both during life and post mortem, in contrast to the normal +anatomical structures. This work cannot be said to have originated +with him; for as early as 1679 Bonnet had made similar, although less +extensive, studies; and later many investigators, such as Lancisi and +Haller, had made post-mortem studies. But Morgagni's De sedibus et +causis morborum per anatomen indagatis was the largest, most accurate, +and best-illustrated collection of cases that had ever been brought +together, and marks an epoch in medical science. From the time of the +publication of Morgagni's researches, morbid anatomy became a recognized +branch of the medical science, and the effect of the impetus thus given +it has been steadily increasing since that time. + + +WILLIAM HUNTER + +William Hunter (1718-1783) must always be remembered as one of the +greatest physicians and anatomists of the eighteenth century, and +particularly as the first great teacher of anatomy in England; but his +fame has been somewhat overshadowed by that of his younger brother John. + +Hunter had been intended and educated for the Church, but on the advice +of the surgeon William Cullen he turned his attention to the study of +medicine. His first attempt at teaching was in 1746, when he delivered +a series of lectures on surgery for the Society of Naval Practitioners. +These lectures proved so interesting and instructive that he was at +once invited to give others, and his reputation as a lecturer was soon +established. He was a natural orator and story-teller, and he combined +with these attractive qualities that of thoroughness and clearness in +demonstrations, and although his lectures were two hours long he made +them so full of interest that his pupils seldom tired of listening. +He believed that he could do greater good to the world by "publicly +teaching his art than by practising it," and even during the last few +days of his life, when he was so weak that his friends remonstrated +against it, he continued his teaching, fainting from exhaustion at the +end of his last lecture, which preceded his death by only a few days. + +For many years it was Hunter's ambition to establish a museum where the +study of anatomy, surgery, and medicine might be advanced, and in 1765 +he asked for a grant of a plot of ground for this purpose, offering to +spend seven thousand pounds on its erection besides endowing it with a +professorship of anatomy. Not being able to obtain this grant, however, +he built a house, in which were lecture and dissecting rooms, and his +museum. In this museum were anatomical preparations, coins, minerals, +and natural-history specimens. + +Hunter's weakness was his love of controversy and his resentment of +contradiction. This brought him into strained relations with many of +the leading physicians of his time, notably his own brother John, who +himself was probably not entirely free from blame in the matter. Hunter +is said to have excused his own irritability on the grounds that being +an anatomist, and accustomed to "the passive submission of dead bodies," +contradictions became the more unbearable. Many of the physiological +researches begun by him were carried on and perfected by his more famous +brother, particularly his investigations of the capillaries, but he +added much to the anatomical knowledge of several structures of the +body, notably as to the structure of cartilages and joints. + + +JOHN HUNTER + +In Abbot Islip's chapel in Westminster Abbey, close to the resting-place +of Ben Jonson, rest the remains of John Hunter (1728-1793), famous in +the annals of medicine as among the greatest physiologists and surgeons +that the world has ever produced: a man whose discoveries and inventions +are counted by scores, and whose field of research was only limited by +the outermost boundaries of eighteenth-century science, although his +efforts were directed chiefly along the lines of his profession. + +Until about twenty years of age young Hunter had shown little aptitude +for study, being unusually fond of out-door sports and amusements; but +about that time, realizing that some occupation must be selected, he +asked permission of his brother William to attempt some dissections in +his anatomical school in London. To the surprise of his brother he made +this dissection unusually well; and being given a second, he acquitted +himself with such skill that his brother at once predicted that he would +become a great anatomist. Up to this time he had had no training of +any kind to prepare him for his professional career, and knew little of +Greek or Latin--languages entirely unnecessary for him, as he proved +in all of his life work. Ottley tells the story that, when twitted with +this lack of knowledge of the "dead languages" in after life, he said +of his opponent, "I could teach him that on the dead body which he never +knew in any language, dead or living." + +By his second year in dissection he had become so skilful that he was +given charge of some of the classes in his brother's school; in 1754 he +became a surgeon's pupil in St. George's Hospital, and two years later +house-surgeon. Having by overwork brought on symptoms that seemed to +threaten consumption, he accepted the position of staff-surgeon to an +expedition to Belleisle in 1760, and two years later was serving with +the English army at Portugal. During all this time he was constantly +engaged in scientific researches, many of which, such as his +observations of gun-shot wounds, he put to excellent use in later life. +On returning to England much improved in health in 1763, he entered at +once upon his career as a London surgeon, and from that time forward +his progress was a practically uninterrupted series of successes in his +profession. + +Hunter's work on the study of the lymphatics was of great service to +the medical profession. This important net-work of minute vessels +distributed throughout the body had recently been made the object of +much study, and various students, including Haller, had made extensive +investigations since their discovery by Asellius. But Hunter, in 1758, +was the first to discover the lymphatics in the neck of birds, although +it was his brother William who advanced the theory that the function +of these vessels was that of absorbents. One of John Hunter's pupils, +William Hewson (1739-1774), first gave an account, in 1768, of +the lymphatics in reptiles and fishes, and added to his teacher's +investigations of the lymphatics in birds. These studies of the +lymphatics have been regarded, perhaps with justice, as Hunter's most +valuable contributions to practical medicine. + +In 1767 he met with an accident by which he suffered a rupture of +the tendo Achillis--the large tendon that forms the attachment of the +muscles of the calf to the heel. From observations of this accident, +and subsequent experiments upon dogs, he laid the foundation for the +now simple and effective operation for the cure of club feet and other +deformities involving the tendons. In 1772 he moved into his residence +at Earlscourt, Brompton, where he gathered about him a great menagerie +of animals, birds, reptiles, insects, and fishes, which he used in his +physiological and surgical experiments. Here he performed a countless +number of experiments--more, probably, than "any man engaged in +professional practice has ever conducted." These experiments varied +in nature from observations of the habits of bees and wasps to major +surgical operations performed upon hedgehogs, dogs, leopards, etc. It +is said that for fifteen years he kept a flock of geese for the sole +purpose of studying the process of development in eggs. + +Hunter began his first course of lectures in 1772, being forced to do +this because he had been so repeatedly misquoted, and because he felt +that he could better gauge his own knowledge in this way. Lecturing was +a sore trial to him, as he was extremely diffident, and without writing +out his lectures in advance he was scarcely able to speak at all. In +this he presented a marked contrast to his brother William, who was +a fluent and brilliant speaker. Hunter's lectures were at best simple +readings of the facts as he had written them, the diffident teacher +seldom raising his eyes from his manuscript and rarely stopping +until his complete lecture had been read through. His lectures were, +therefore, instructive rather than interesting, as he used infinite care +in preparing them; but appearing before his classes was so dreaded by +him that he is said to have been in the habit of taking a half-drachm of +laudanum before each lecture to nerve him for the ordeal. One is led to +wonder by what name he shall designate that quality of mind that renders +a bold and fearless surgeon like Hunter, who is undaunted in the face +of hazardous and dangerous operations, a stumbling, halting, and +"frightened" speaker before a little band of, at most, thirty young +medical students. And yet this same thing is not unfrequently seen among +the boldest surgeons. + + +Hunter's Operation for the Cure of Aneurisms + +It should be an object-lesson to those who, ignorantly or otherwise, +preach against the painless vivisection as practised to-day, that by the +sacrifice of a single deer in the cause of science Hunter discovered a +fact in physiology that has been the means of saving thousands of human +lives and thousands of human bodies from needless mutilation. We refer +to the discovery of the "collateral circulation" of the blood, +which led, among other things, to Hunter's successful operation upon +aneurisms. + +Simply stated, every organ or muscle of the body is supplied by one +large artery, whose main trunk distributes the blood into its lesser +branches, and thence through the capillaries. Cutting off this main +artery, it would seem, should cut off entirely the blood-supply to the +particular organ which is supplied by this vessel; and until the time of +Hunter's demonstration this belief was held by most physiologists. But +nature has made a provision for this possible stoppage of blood-supply +from a single source, and has so arranged that some of the small +arterial branches coming from the main supply-trunk are connected with +other arterial branches coming from some other supply-trunk. Under +normal conditions the main arterial trunks supply their respective +organs, the little connecting arterioles playing an insignificant part. +But let the main supply-trunk be cut off or stopped for whatever reason, +and a remarkable thing takes place. The little connecting branches +begin at once to enlarge and draw blood from the neighboring uninjured +supply-trunk, This enlargement continues until at last a new route for +the circulation has been established, the organ no longer depending +on the now defunct original arterial trunk, but getting on as well as +before by this "collateral" circulation that has been established. + +The thorough understanding of this collateral circulation is one of the +most important steps in surgery, for until it was discovered amputations +were thought necessary in such cases as those involving the artery +supplying a leg or arm, since it was supposed that, the artery being +stopped, death of the limb and the subsequent necessity for amputation +were sure to follow. Hunter solved this problem by a single operation +upon a deer, and his practicality as a surgeon led him soon after to +apply this knowledge to a certain class of surgical cases in a most +revolutionary and satisfactory manner. + +What led to Hunter's far-reaching discovery was his investigation as to +the cause of the growth of the antlers of the deer. Wishing to ascertain +just what part the blood-supply on the opposite sides of the neck played +in the process of development, or, perhaps more correctly, to see what +effect cutting off the main blood-supply would have, Hunter had one of +the deer of Richmond Park caught and tied, while he placed a ligature +around one of the carotid arteries--one of the two principal arteries +that supply the head with blood. He observed that shortly after this the +antler (which was only half grown and consequently very vascular) on the +side of the obliterated artery became cold to the touch--from the lack +of warmth-giving blood. There was nothing unexpected in this, and Hunter +thought nothing of it until a few days later, when he found, to his +surprise, that the antler had become as warm as its fellow, and was +apparently increasing in size. Puzzled as to how this could be, and +suspecting that in some way his ligature around the artery had not been +effective, he ordered the deer killed, and on examination was astonished +to find that while his ligature had completely shut off the blood-supply +from the source of that carotid artery, the smaller arteries had become +enlarged so as to supply the antler with blood as well as ever, only by +a different route. + +Hunter soon had a chance to make a practical application of the +knowledge thus acquired. This was a case of popliteal aneurism, +operations for which had heretofore proved pretty uniformly fatal. An +aneurism, as is generally understood, is an enlargement of a certain +part of an artery, this enlargement sometimes becoming of enormous size, +full of palpitating blood, and likely to rupture with fatal results at +any time. If by any means the blood can be allowed to remain quiet for +even a few hours in this aneurism it will form a clot, contract, and +finally be absorbed and disappear without any evil results. The problem +of keeping the blood quiet, with the heart continually driving it +through the vessel, is not a simple one, and in Hunter's time was +considered so insurmountable that some surgeons advocated amputation +of any member having an aneurism, while others cut down upon the tumor +itself and attempted to tie off the artery above and below. The first +of these operations maimed the patient for life, while the second was +likely to prove fatal. + +In pondering over what he had learned about collateral circulation and +the time required for it to become fully established, Hunter conceived +the idea that if the blood-supply was cut off from above the aneurism, +thus temporarily preventing the ceaseless pulsations from the heart, +this blood would coagulate and form a clot before the collateral +circulation could become established or could affect it. The patient +upon whom he performed his now celebrated operation was afflicted with +a popliteal aneurism--that is, the aneurism was located on the large +popliteal artery just behind the knee-joint. Hunter, therefore, tied off +the femoral, or main supplying artery in the thigh, a little distance +above the aneurism. The operation was entirely successful, and in six +weeks' time the patient was able to leave the hospital, and with two +sound limbs. Naturally the simplicity and success of this operation +aroused the attention of Europe, and, alone, would have made the name of +Hunter immortal in the annals of surgery. The operation has ever since +been called the "Hunterian" operation for aneurism, but there is reason +to believe that Dominique Anel (born about 1679) performed a somewhat +similar operation several years earlier. It is probable, however, that +Hunter had never heard of this work of Anel, and that his operation +was the outcome of his own independent reasoning from the facts he had +learned about collateral circulation. Furthermore, Hunter's mode of +operation was a much better one than Anel's, and, while Anel's must +claim priority, the credit of making it widely known will always be +Hunter's. + +The great services of Hunter were recognized both at home and abroad, +and honors and positions of honor and responsibility were given him. In +1776 he was appointed surgeon-extraordinary to the king; in 1783 he +was elected a member of the Royal Society of Medicine and of the Royal +Academy of Surgery at Paris; in 1786 he became deputy surgeon-general +of the army; and in 1790 he was appointed surgeon-general and +inspector-general of hospitals. All these positions he filled with +credit, and he was actively engaged in his tireless pursuit of knowledge +and in discharging his many duties when in October, 1793, he was +stricken while addressing some colleagues, and fell dead in the arms of +a fellow-physician. + + +LAZZARO SPALLANZANI + +Hunter's great rival among contemporary physiologists was the Italian +Lazzaro Spallanzani (1729-1799), one of the most picturesque figures +in the history of science. He was not educated either as a scientist or +physician, devoting, himself at first to philosophy and the languages, +afterwards studying law, and later taking orders. But he was a keen +observer of nature and of a questioning and investigating mind, so that +he is remembered now chiefly for his discoveries and investigations +in the biological sciences. One important demonstration was his +controversion of the theory of abiogenesis, or "spontaneous generation," +as propounded by Needham and Buffon. At the time of Needham's +experiments it had long been observed that when animal or vegetable +matter had lain in water for a little time--long enough for it to begin +to undergo decomposition--the water became filled with microscopic +creatures, the "infusoria animalculis." This would tend to show, either +that the water or the animal or vegetable substance contained the +"germs" of these minute organisms, or else that they were generated +spontaneously. It was known that boiling killed these animalcules, +and Needham agreed, therefore, that if he first heated the meat or +vegetables, and also the water containing them, and then placed them in +hermetically scaled jars--if he did this, and still the animalcules +made their appearance, it would be proof-positive that they had been +generated spontaneously. Accordingly he made numerous experiments, +always with the same results--that after a few days the water was found +to swarm with the microscopic creatures. The thing seemed proven beyond +question--providing, of course, that there had been no slips in the +experiments. + +But Abbe Spallanzani thought that he detected such slips in Needham's +experiment. The possibility of such slips might come in several ways: +the contents of the jar might not have been boiled for a sufficient +length of time to kill all the germs, or the air might not have +been excluded completely by the sealing process. To cover both these +contingencies, Spallanzani first hermetically sealed the glass vessels +and then boiled them for three-quarters of an hour. Under these +circumstances no animalcules ever made their appearance--a conclusive +demonstration that rendered Needham's grounds for his theory at once +untenable.(2) + +Allied to these studies of spontaneous generation were Spallanzani's +experiments and observations on the physiological processes of +generation among higher animals. He experimented with frogs, tortoises, +and dogs; and settled beyond question the function of the ovum and +spermatozoon. Unfortunately he misinterpreted the part played by the +spermatozoa in believing that their surrounding fluid was equally active +in the fertilizing process, and it was not until some forty years later +(1824) that Dumas corrected this error. + + +THE CHEMICAL THEORY OF DIGESTION + +Among the most interesting researches of Spallanzani were his +experiments to prove that digestion, as carried on in the stomach, is a +chemical process. In this he demonstrated, as Rene Reaumur had attempted +to demonstrate, that digestion could be carried on outside the walls of +the stomach as an ordinary chemical reaction, using the gastric juice +as the reagent for performing the experiment. The question as to whether +the stomach acted as a grinding or triturating organ, rather than as a +receptacle for chemical action, had been settled by Reaumur and was +no longer a question of general dispute. Reaumur had demonstrated +conclusively that digestion would take place in the stomach in the same +manner and the same time if the substance to be digested was protected +from the peristalic movements of the stomach and subjected to the action +of the gastric juice only. He did this by introducing the substances to +be digested into the stomach in tubes, and thus protected so that while +the juices of the stomach could act upon them freely they would not be +affected by any movements of the organ. + +Following up these experiments, he attempted to show that digestion +could take place outside the body as well as in it, as it certainly +should if it were a purely chemical process. He collected quantities +of gastric juice, and placing it in suitable vessels containing crushed +grain or flesh, kept the mixture at about the temperature of the body +for several hours. After repeated experiments of this kind, apparently +conducted with great care, Reaumur reached the conclusion that "the +gastric juice has no more effect out of the living body in dissolving +or digesting the food than water, mucilage, milk, or any other bland +fluid."(3) Just why all of these experiments failed to demonstrate a +fact so simple does not appear; but to Spallanzani, at least, they +were by no means conclusive, and he proceeded to elaborate upon the +experiments of Reaumur. He made his experiments in scaled tubes exposed +to a certain degree of heat, and showed conclusively that the chemical +process does go on, even when the food and gastric juice are removed +from their natural environment in the stomach. In this he was opposed +by many physiologists, among them John Hunter, but the truth of his +demonstrations could not be shaken, and in later years we find Hunter +himself completing Spallanzani's experiments by his studies of the +post-mortem action of the gastric juice upon the stomach walls. + +That Spallanzani's and Hunter's theories of the action of the gastric +juice were not at once universally accepted is shown by an essay written +by a learned physician in 1834. In speaking of some of Spallanzani's +demonstrations, he writes: "In some of the experiments, in order to give +the flesh or grains steeped in the gastric juice the same temperature +with the body, the phials were introduced under the armpits. But this is +not a fair mode of ascertaining the effects of the gastric juice out of +the body; for the influence which life may be supposed to have on the +solution of the food would be secured in this case. The affinities +connected with life would extend to substances in contact with any part +of the system: substances placed under the armpits are not placed at +least in the same circumstances with those unconnected with a living +animal." But just how this writer reaches the conclusion that "the +experiments of Reaumur and Spallanzani give no evidence that the gastric +juice has any peculiar influence more than water or any other bland +fluid in digesting the food"(4) is difficult to understand. + +The concluding touches were given to the new theory of digestion by +John Hunter, who, as we have seen, at first opposed Spallanzani, but +who finally became an ardent champion of the chemical theory. Hunter now +carried Spallanzani's experiments further and proved the action of the +digestive fluids after death. For many years anatomists had been puzzled +by pathological lesion of the stomach, found post mortem, when no +symptoms of any disorder of the stomach had been evinced during life. +Hunter rightly conceived that these lesions were caused by the action +of the gastric juice, which, while unable to act upon the living tissue, +continued its action chemically after death, thus digesting the walls +of the stomach in which it had been formed. And, as usual with his +observations, he turned this discovery to practical use in accounting +for certain phenomena of digestion. The following account of the stomach +being digested after death was written by Hunter at the desire of +Sir John Pringle, when he was president of the Royal Society, and the +circumstance which led to this is as follows: "I was opening, in his +presence, the body of a patient of his own, where the stomach was in +part dissolved, which appeared to him very unaccountable, as there had +been no previous symptom that could have led him to suspect any +disease in the stomach. I took that opportunity of giving him my ideas +respecting it, and told him that I had long been making experiments +on digestion, and considered this as one of the facts which proved a +converting power in the gastric juice.... There are a great many powers +in nature which the living principle does not enable the animal matter, +with which it is combined, to resist--viz., the mechanical and most +of the strongest chemical solvents. It renders it, however, capable of +resisting the powers of fermentation, digestion, and perhaps several +others, which are well known to act on the same matter when deprived of +the living principle and entirely to decompose it." + +Hunter concludes his paper with the following paragraph: "These +appearances throw considerable light on the principle of digestion, +and show that it is neither a mechanical power, nor contractions of the +stomach, nor heat, but something secreted in the coats of the stomach, +and thrown into its cavity, which there animalizes the food or +assimilates it to the nature of the blood. The power of this juice is +confined or limited to certain substances, especially of the vegetable +and animal kingdoms; and although this menstruum is capable of acting +independently of the stomach, yet it is indebted to that viscus for its +continuance."(5) + + +THE FUNCTION OF RESPIRATION + +It is a curious commentary on the crude notions of mechanics of previous +generations that it should have been necessary to prove by experiment +that the thin, almost membranous stomach of a mammal has not the power +to pulverize, by mere attrition, the foods that are taken into it. +However, the proof was now for the first time forthcoming, and the +question of the general character of the function of digestion was +forever set at rest. Almost simultaneously with this great advance, +corresponding progress was made in an allied field: the mysteries of +respiration were at last cleared up, thanks to the new knowledge of +chemistry. The solution of the problem followed almost as a matter +of course upon the advances of that science in the latter part of the +century. Hitherto no one since Mayow, of the previous century, whose +flash of insight had been strangely overlooked and forgotten, had even +vaguely surmised the true function of the lungs. The great Boerhaave +had supposed that respiration is chiefly important as an aid to the +circulation of the blood; his great pupil, Haller, had believed to the +day of his death in 1777 that the main purpose of the function is to +form the voice. No genius could hope to fathom the mystery of the lungs +so long as air was supposed to be a simple element, serving a mere +mechanical purpose in the economy of the earth. + +But the discovery of oxygen gave the clew, and very soon all the +chemists were testing the air that came from the lungs--Dr. Priestley, +as usual, being in the van. His initial experiments were made in +1777, and from the outset the problem was as good as solved. Other +experimenters confirmed his results in all their essentials--notably +Scheele and Lavoisier and Spallanzani and Davy. It was clearly +established that there is chemical action in the contact of the air with +the tissue of the lungs; that some of the oxygen of the air disappears, +and that carbonic-acid gas is added to the inspired air. It was shown, +too, that the blood, having come in contact with the air, is changed +from black to red in color. These essentials were not in dispute from +the first. But as to just what chemical changes caused these results +was the subject of controversy. Whether, for example, oxygen is actually +absorbed into the blood, or whether it merely unites with carbon given +off from the blood, was long in dispute. + +Each of the main disputants was biased by his own particular views as +to the moot points of chemistry. Lavoisier, for example, believed oxygen +gas to be composed of a metal oxygen combined with the alleged element +heat; Dr. Priestley thought it a compound of positive electricity and +phlogiston; and Humphry Davy, when he entered the lists a little later, +supposed it to be a compound of oxygen and light. Such mistaken notions +naturally complicated matters and delayed a complete understanding of +the chemical processes of respiration. It was some time, too, before the +idea gained acceptance that the most important chemical changes do not +occur in the lungs themselves, but in the ultimate tissues. Indeed, +the matter was not clearly settled at the close of the century. +Nevertheless, the problem of respiration had been solved in its +essentials. Moreover, the vastly important fact had been established +that a process essentially identical with respiration is necessary to +the existence not only of all creatures supplied with lungs, but to +fishes, insects, and even vegetables--in short, to every kind of living +organism. + + +ERASMUS DARWIN AND VEGETABLE PHYSIOLOGY + +Some interesting experiments regarding vegetable respiration were made +just at the close of the century by Erasmus Darwin, and recorded in his +Botanic Garden as a foot-note to the verse: + +"While spread in air the leaves respiring play." + + +These notes are worth quoting at some length, as they give a clear idea +of the physiological doctrines of the time (1799), while taking advance +ground as to the specific matter in question: + + +"There have been various opinions," Darwin says, "concerning the use of +the leaves of plants in the vegetable economy. Some have contended +that they are perspiratory organs. This does not seem probable from an +experiment of Dr. Hales, Vegetable Statics, p. 30. He, found, by cutting +off branches of trees with apples on them and taking off the leaves, +that an apple exhaled about as much as two leaves the surfaces of which +were nearly equal to the apple; whence it would appear that apples have +as good a claim to be termed perspiratory organs as leaves. Others have +believed them excretory organs of excrementitious juices, but as +the vapor exhaled from vegetables has no taste, this idea is no more +probable than the other; add to this that in most weathers they do not +appear to perspire or exhale at all. + +"The internal surface of the lungs or air-vessels in men is said to +be equal to the external surface of the whole body, or almost fifteen +square feet; on this surface the blood is exposed to the influence of +the respired air through the medium, however, of a thin pellicle; by +this exposure to the air it has its color changed from deep red to +bright scarlet, and acquires something so necessary to the existence of +life that we can live scarcely a minute without this wonderful process. + +"The analogy between the leaves of plants and the lungs or gills of +animals seems to embrace so many circumstances that we can scarcely +withhold our consent to their performing similar offices. + +"1. The great surface of leaves compared to that of the trunk and +branches of trees is such that it would seem to be an organ well adapted +for the purpose of exposing the vegetable juices to the influence of the +air; this, however, we shall see afterwards is probably performed only +by their upper surfaces, yet even in this case the surface of the leaves +in general bear a greater proportion to the surface of the tree than the +lungs of animals to their external surfaces. + +"2. In the lung of animals the blood, after having been exposed to the +air in the extremities of the pulmonary artery, is changed in color +from deep red to bright scarlet, and certainly in some of its essential +properties it is then collected by the pulmonary vein and returned +to the heart. To show a similarity of circumstances in the leaves of +plants, the following experiment was made, June 24, 1781. A stalk with +leaves and seed-vessels of large spurge (Euphorbia helioscopia) had been +several days placed in a decoction of madder (Rubia tinctorum) so that +the lower part of the stem and two of the undermost leaves were immersed +in it. After having washed the immersed leaves in clear water I could +readily discover the color of the madder passing along the middle rib +of each leaf. The red artery was beautifully visible on the under and on +the upper surface of the leaf; but on the upper side many red branches +were seen going from it to the extremities of the leaf, which on the +other side were not visible except by looking through it against the +light. On this under side a system of branching vessels carrying a +pale milky fluid were seen coming from the extremities of the leaf, and +covering the whole under side of it, and joining two large veins, one +on each side of the red artery in the middle rib of the leaf, and along +with it descending to the foot-stalk or petiole. On slitting one of +these leaves with scissors, and having a magnifying-glass ready, the +milky blood was seen oozing out of the returning veins on each side of +the red artery in the middle rib, but none of the red fluid from the +artery. + +"All these appearances were more easily seen in a leaf of Picris treated +in the same manner; for in this milky plant the stems and middle rib of +the leaves are sometimes naturally colored reddish, and hence the color +of the madder seemed to pass farther into the ramifications of their +leaf-arteries, and was there beautifully visible with the returning +branches of milky veins on each side." + + +Darwin now goes on to draw an incorrect inference from his observations: + + +"3. From these experiments," he says, "the upper surface of the leaf +appeared to be the immediate organ of respiration, because the colored +fluid was carried to the extremities of the leaf by vessels most +conspicuous on the upper surface, and there changed into a milky fluid, +which is the blood of the plant, and then returned by concomitant +veins on the under surface, which were seen to ooze when divided with +scissors, and which, in Picris, particularly, render the under surface +of the leaves greatly whiter than the upper one." + + +But in point of fact, as studies of a later generation were to show, it +is the under surface of the leaf that is most abundantly provided +with stomata, or "breathing-pores." From the stand-point of this later +knowledge, it is of interest to follow our author a little farther, +to illustrate yet more fully the possibility of combining correct +observations with a faulty inference. + + +"4. As the upper surface of leaves constitutes the organ of respiration, +on which the sap is exposed in the termination of arteries beneath a +thin pellicle to the action of the atmosphere, these surfaces in many +plants strongly repel moisture, as cabbage leaves, whence the particles +of rain lying over their surfaces without touching them, as observed by +Mr. Melville (Essays Literary and Philosophical: Edinburgh), have the +appearance of globules of quicksilver. And hence leaves with the upper +surfaces on water wither as soon as in the dry air, but continue green +for many days if placed with the under surface on water, as appears +in the experiments of Monsieur Bonnet (Usage des Feuilles). Hence some +aquatic plants, as the water-lily (Nymphoea), have the lower sides +floating on the water, while the upper surfaces remain dry in the air. + +"5. As those insects which have many spiracula, or breathing apertures, +as wasps and flies, are immediately suffocated by pouring oil upon them, +I carefully covered with oil the surfaces of several leaves of phlomis, +of Portugal laurel, and balsams, and though it would not regularly +adhere, I found them all die in a day or two. + +"It must be added that many leaves are furnished with muscles about +their foot-stalks, to turn their surfaces to the air or light, as mimosa +or Hedysarum gyrans. From all these analogies I think there can be no +doubt but that leaves of trees are their lungs, giving out a phlogistic +material to the atmosphere, and absorbing oxygen, or vital air. + +"6. The great use of light to vegetation would appear from this theory +to be by disengaging vital air from the water which they perspire, and +thence to facilitate its union with their blood exposed beneath the +thin surface of their leaves; since when pure air is thus applied it +is probable that it can be more readily absorbed. Hence, in the curious +experiments of Dr. Priestley and Mr. Ingenhouz, some plants purified +less air than others--that is, they perspired less in the sunshine; +and Mr. Scheele found that by putting peas into water which about +half covered them they converted the vital air into fixed air, or +carbonic-acid gas, in the same manner as in animal respiration. + +"7. The circulation in the lungs or leaves of plants is very similar +to that of fish. In fish the blood, after having passed through their +gills, does not return to the heart as from the lungs of air-breathing +animals, but the pulmonary vein taking the structure of an artery after +having received the blood from the gills, which there gains a more +florid color, distributes it to the other parts of their bodies. The +same structure occurs in the livers of fish, whence we see in those +animals two circulations independent of the power of the heart--viz., +that beginning at the termination of the veins of the gills and +branching through the muscles, and that which passes through the liver; +both which are carried on by the action of those respective arteries and +veins."(6) + +Darwin is here a trifle fanciful in forcing the analogy between plants +and animals. The circulatory system of plants is really not quite +so elaborately comparable to that of fishes as he supposed. But the +all-important idea of the uniformity underlying the seeming diversity +of Nature is here exemplified, as elsewhere in the writings of Erasmus +Darwin; and, more specifically, a clear grasp of the essentials of the +function of respiration is fully demonstrated. + + +ZOOLOGY AT THE CLOSE OF THE EIGHTEENTH CENTURY + + +Several causes conspired to make exploration all the fashion during the +closing epoch of the eighteenth century. New aid to the navigator +had been furnished by the perfected compass and quadrant, and by the +invention of the chronometer; medical science had banished scurvy, which +hitherto had been a perpetual menace to the voyager; and, above all, the +restless spirit of the age impelled the venturesome to seek novelty in +fields altogether new. Some started for the pole, others tried for a +northeast or northwest passage to India, yet others sought the great +fictitious antarctic continent told of by tradition. All these of course +failed of their immediate purpose, but they added much to the world's +store of knowledge and its fund of travellers' tales. + +Among all these tales none was more remarkable than those which told of +strange living creatures found in antipodal lands. And here, as did not +happen in every field, the narratives were often substantiated by the +exhibition of specimens that admitted no question. Many a company of +explorers returned more or less laden with such trophies from the +animal and vegetable kingdoms, to the mingled astonishment, delight, and +bewilderment of the closet naturalists. The followers of Linnaeus in the +"golden age of natural history," a few decades before, had increased the +number of known species of fishes to about four hundred, of birds to one +thousand, of insects to three thousand, and of plants to ten thousand. +But now these sudden accessions from new territories doubled the figure +for plants, tripled it for fish and birds, and brought the number of +described insects above twenty thousand. Naturally enough, this wealth +of new material was sorely puzzling to the classifiers. The more +discerning began to see that the artificial system of Linnaeus, +wonderful and useful as it had been, must be advanced upon before the +new material could be satisfactorily disposed of. The way to a more +natural system, based on less arbitrary signs, had been pointed out by +Jussieu in botany, but the zoologists were not prepared to make headway +towards such a system until they should gain a wider understanding of +the organisms with which they had to deal through comprehensive studies +of anatomy. Such studies of individual forms in their relations to the +entire scale of organic beings were pursued in these last decades of +the century, but though two or three most important generalizations were +achieved (notably Kaspar Wolff's conception of the cell as the basis of +organic life, and Goethe's all-important doctrine of metamorphosis of +parts), yet, as a whole, the work of the anatomists of the period was +germinative rather than fruit-bearing. Bichat's volumes, telling of the +recognition of the fundamental tissues of the body, did not begin to +appear till the last year of the century. The announcement by Cuvier of +the doctrine of correlation of parts bears the same date, but in general +the studies of this great naturalist, which in due time were to stamp +him as the successor of Linnaeus, were as yet only fairly begun. + + + + +V. ANATOMY AND PHYSIOLOGY IN THE NINETEENTH CENTURY + +CUVIER AND THE CORRELATION OF PARTS + +We have seen that the focal points of the physiological world towards +the close of the eighteenth century were Italy and England, but when +Spallanzani and Hunter passed away the scene shifted to France. The +time was peculiarly propitious, as the recent advances in many lines of +science had brought fresh data for the student of animal life which were +in need of classification, and, as several minds capable of such a task +were in the field, it was natural that great generalizations should have +come to be quite the fashion. Thus it was that Cuvier came forward with +a brand-new classification of the animal kingdom, establishing +four great types of being, which he called vertebrates, mollusks, +articulates, and radiates. Lamarck had shortly before established the +broad distinction between animals with and those without a backbone; +Cuvier's Classification divided the latter--the invertebrates--into +three minor groups. And this division, familiar ever since to all +students of zoology, has only in very recent years been supplanted, and +then not by revolution, but by a further division, which the elaborate +recent studies of lower forms of life seemed to make desirable. + +In the course of those studies of comparative anatomy which led to his +new classification, Cuvier's attention was called constantly to the +peculiar co-ordination of parts in each individual organism. Thus an +animal with sharp talons for catching living prey--as a member of the +cat tribe--has also sharp teeth, adapted for tearing up the flesh of its +victim, and a particular type of stomach, quite different from that of +herbivorous creatures. This adaptation of all the parts of the animal +to one another extends to the most diverse parts of the organism, and +enables the skilled anatomist, from the observation of a single typical +part, to draw inferences as to the structure of the entire animal--a +fact which was of vast aid to Cuvier in his studies of paleontology. It +did not enable Cuvier, nor does it enable any one else, to reconstruct +fully the extinct animal from observation of a single bone, as has +sometimes been asserted, but what it really does establish, in the hands +of an expert, is sufficiently astonishing. + +"While the study of the fossil remains of the greater quadrupeds is more +satisfactory," he writes, "by the clear results which it affords, than +that of the remains of other animals found in a fossil state, it is also +complicated with greater and more numerous difficulties. Fossil shells +are usually found quite entire, and retaining all the characters +requisite for comparing them with the specimens contained in collections +of natural history, or represented in the works of naturalists. Even the +skeletons of fishes are found more or less entire, so that the general +forms of their bodies can, for the most part, be ascertained, +and usually, at least, their generic and specific characters are +determinable, as these are mostly drawn from their solid parts. In +quadrupeds, on the contrary, even when their entire skeletons are +found, there is great difficulty in discovering their distinguishing +characters, as these are chiefly founded upon their hairs and colors and +other marks which have disappeared previous to their incrustation. It is +also very rare to find any fossil skeletons of quadrupeds in any degree +approaching to a complete state, as the strata for the most part only +contain separate bones, scattered confusedly and almost always broken +and reduced to fragments, which are the only means left to naturalists +for ascertaining the species or genera to which they have belonged. + +"Fortunately comparative anatomy, when thoroughly understood, enables +us to surmount all these difficulties, as a careful application of its +principles instructs us in the correspondences and dissimilarities of +the forms of organized bodies of different kinds, by which each may be +rigorously ascertained from almost every fragment of its various parts +and organs. + +"Every organized individual forms an entire system of its own, all the +parts of which naturally correspond, and concur to produce a certain +definite purpose, by reciprocal reaction, or by combining towards the +same end. Hence none of these separate parts can change their forms +without a corresponding change in the other parts of the same animal, +and consequently each of these parts, taken separately, indicates all +the other parts to which it has belonged. Thus, as I have elsewhere +shown, if the viscera of an animal are so organized as only to be fitted +for the digestion of recent flesh, it is also requisite that the jaws +should be so constructed as to fit them for devouring prey; the claws +must be constructed for seizing and tearing it to pieces; the teeth +for cutting and dividing its flesh; the entire system of the limbs, +or organs of motion, for pursuing and overtaking it; and the organs of +sense for discovering it at a distance. Nature must also have endowed +the brain of the animal with instincts sufficient for concealing itself +and for laying plans to catch its necessary victims.... + +"To enable the animal to carry off its prey when seized, a corresponding +force is requisite in the muscles which elevate the head, and this +necessarily gives rise to a determinate form of the vertebrae to which +these muscles are attached and of the occiput into which they are +inserted. In order that the teeth of a carnivorous animal may be able to +cut the flesh, they require to be sharp, more or less so in proportion +to the greater or less quantity of flesh that they have to cut. It is +requisite that their roots should be solid and strong, in proportion to +the quantity and size of the bones which they have to break to pieces. +The whole of these circumstances must necessarily influence the +development and form of all the parts which contribute to move the +jaws...." + +After these observations, it will be easily seen that similar +conclusions may be drawn with respect to the limbs of carnivorous +animals, which require particular conformations to fit them for rapidity +of motion in general; and that similar considerations must influence the +forms and connections of the vertebrae and other bones constituting the +trunk of the body, to fit them for flexibility and readiness of motion +in all directions. The bones also of the nose, of the orbit, and of +the ears require certain forms and structures to fit them for giving +perfection to the senses of smell, sight, and hearing, so necessary to +animals of prey. In short, the shape and structure of the teeth regulate +the forms of the condyle, of the shoulder-blade, and of the claws, +in the same manner as the equation of a curve regulates all its other +properties; and as in regard to any particular curve all its properties +may be ascertained by assuming each separate property as the foundation +of a particular equation, in the same manner a claw, a shoulder-blade, +a condyle, a leg or arm bone, or any other bone separately considered, +enables us to discover the description of teeth to which they have +belonged; and so also reciprocally we may determine the forms of the +other bones from the teeth. Thus commencing our investigations by a +careful survey of any one bone by itself, a person who is sufficiently +master of the laws of organic structure may, as it were, reconstruct the +whole animal to which that bone belonged."(1) + +We have already pointed out that no one is quite able to perform the +necromantic feat suggested in the last sentence; but the exaggeration is +pardonable in the enthusiast to whom the principle meant so much and in +whose hands it extended so far. + +Of course this entire principle, in its broad outlines, is something +with which every student of anatomy had been familiar from the time +when anatomy was first studied, but the full expression of the "law +of co-ordination," as Cuvier called it, had never been explicitly made +before; and, notwithstanding its seeming obviousness, the exposition +which Cuvier made of it in the introduction to his classical work on +comparative anatomy, which was published during the first decade of +the nineteenth century, ranks as a great discovery. It is one of those +generalizations which serve as guideposts to other discoveries. + + +BICHAT AND THE BODILY TISSUES + +Much the same thing may be said of another generalization regarding the +animal body, which the brilliant young French physician Marie Francois +Bichat made in calling attention to the fact that each vertebrate +organism, including man, has really two quite different sets of +organs--one set under volitional control, and serving the end of +locomotion, the other removed from volitional control, and serving the +ends of the "vital processes" of digestion, assimilation, and the like. +He called these sets of organs the animal system and the organic system, +respectively. The division thus pointed out was not quite new, for +Grimaud, professor of physiology in the University of Montpellier, +had earlier made what was substantially the same classification of the +functions into "internal or digestive and external or locomotive"; but +it was Bichat's exposition that gave currency to the idea. + +Far more important, however, was another classification which Bichat put +forward in his work on anatomy, published just at the beginning of the +last century. This was the division of all animal structures into what +Bichat called tissues, and the pointing out that there are really only +a few kinds of these in the body, making up all the diverse organs. Thus +muscular organs form one system; membranous organs another; glandular +organs a third; the vascular mechanism a fourth, and so on. The +distinction is so obvious that it seems rather difficult to conceive +that it could have been overlooked by the earliest anatomists; but, in +point of fact, it is only obvious because now it has been familiarly +taught for almost a century. It had never been given explicit expression +before the time of Bichat, though it is said that Bichat himself was +somewhat indebted for it to his master, Desault, and to the famous +alienist Pinel. + +However that may be, it is certain that all subsequent anatomists have +found Bichat's classification of the tissues of the utmost value in +their studies of the animal functions. Subsequent advances were to +show that the distinction between the various tissues is not really +so fundamental as Bichat supposed, but that takes nothing from the +practical value of the famous classification. + +It was but a step from this scientific classification of tissues to a +similar classification of the diseases affecting them, and this was one +of the greatest steps towards placing medicine on the plane of an exact +science. This subject of these branches completely fascinated Bichat, +and he exclaimed, enthusiastically: "Take away some fevers and nervous +trouble, and all else belongs to the kingdom of pathological anatomy." +But out of this enthusiasm came great results. Bichat practised as he +preached, and, believing that it was only possible to understand disease +by observing the symptoms carefully at the bedside, and, if the disease +terminated fatally, by post-mortem examination, he was so arduous in his +pursuit of knowledge that within a period of less than six months he had +made over six hundred autopsies--a record that has seldom, if ever, +been equalled. Nor were his efforts fruitless, as a single example will +suffice to show. By his examinations he was able to prove that diseases +of the chest, which had formerly been classed under the indefinite name +"peripneumonia," might involve three different structures, the pleural +sac covering the lungs, the lung itself, and the bronchial tubes, the +diseases affecting these organs being known respectively as pleuritis, +pneumonia, and bronchitis, each one differing from the others as to +prognosis and treatment. The advantage of such an exact classification +needs no demonstration. + + +LISTER AND THE PERFECTED MICROSCOPE + +At the same time when these broad macroscopical distinctions were being +drawn there were other workers who were striving to go even deeper into +the intricacies of the animal mechanism with the aid of the microscope. +This undertaking, however, was beset with very great optical +difficulties, and for a long time little advance was made upon the work +of preceding generations. Two great optical barriers, known technically +as spherical and chromatic aberration--the one due to a failure of the +rays of light to fall all in one plane when focalized through a lens, +the other due to the dispersive action of the lens in breaking the +white light into prismatic colors--confronted the makers of microscopic +lenses, and seemed all but insuperable. The making of achromatic lenses +for telescopes had been accomplished, it is true, by Dolland in the +previous century, by the union of lenses of crown glass with those of +flint glass, these two materials having different indices of refraction +and dispersion. But, aside from the mechanical difficulties which arise +when the lens is of the minute dimensions required for use with the +microscope, other perplexities are introduced by the fact that the use +of a wide pencil of light is a desideratum, in order to gain sufficient +illumination when large magnification is to be secured. + +In the attempt to overcome those difficulties, the foremost physical +philosophers of the time came to the aid of the best opticians. Very +early in the century, Dr. (afterwards Sir David) Brewster, the renowned +Scotch physicist, suggested that certain advantages might accrue from +the use of such gems as have high refractive and low dispersive indices, +in place of lenses made of glass. Accordingly lenses were made of +diamond, of sapphire, and so on, and with some measure of success. But +in 1812 a much more important innovation was introduced by Dr. William +Hyde Wollaston, one of the greatest and most versatile, and, since +the death of Cavendish, by far the most eccentric of English natural +philosophers. This was the suggestion to use two plano-convex +lenses, placed at a prescribed distance apart, in lieu of the single +double-convex lens generally used. This combination largely overcame +the spherical aberration, and it gained immediate fame as the "Wollaston +doublet." + +To obviate loss of light in such a doublet from increase of reflecting +surfaces, Dr. Brewster suggested filling the interspace between the two +lenses with a cement having the same index of refraction as the lenses +themselves--an improvement of manifest advantage. An improvement yet +more important was made by Dr. Wollaston himself in the introduction of +the diaphragm to limit the field of vision between the lenses, instead +of in front of the anterior lens. A pair of lenses thus equipped Dr. +Wollaston called the periscopic microscope. Dr. Brewster suggested that +in such a lens the same object might be attained with greater ease by +grinding an equatorial groove about a thick or globular lens and filling +the groove with an opaque cement. This arrangement found much favor, +and came subsequently to be known as a Coddington lens, though Mr. +Coddington laid no claim to being its inventor. + +Sir John Herschel, another of the very great physicists of the time, +also gave attention to the problem of improving the microscope, and in +1821 he introduced what was called an aplanatic combination of lenses, +in which, as the name implies, the spherical aberration was largely +done away with. It was thought that the use of this Herschel aplanatic +combination as an eyepiece, combined with the Wollaston doublet for the +objective, came as near perfection as the compound microscope was likely +soon to come. But in reality the instrument thus constructed, though +doubtless superior to any predecessor, was so defective that for +practical purposes the simple microscope, such as the doublet or the +Coddington, was preferable to the more complicated one. + +Many opticians, indeed, quite despaired of ever being able to make a +satisfactory refracting compound microscope, and some of them had taken +up anew Sir Isaac Newton's suggestion in reference to a reflecting +microscope. In particular, Professor Giovanni Battista Amici, a very +famous mathematician and practical optician of Modena, succeeded in +constructing a reflecting microscope which was said to be superior to +any compound microscope of the time, though the events of the ensuing +years were destined to rob it of all but historical value. For there +were others, fortunately, who did not despair of the possibilities of +the refracting microscope, and their efforts were destined before +long to be crowned with a degree of success not even dreamed of by any +preceding generation. + +The man to whom chief credit is due for directing those final steps +that made the compound microscope a practical implement instead of a +scientific toy was the English amateur optician Joseph Jackson Lister. +Combining mathematical knowledge with mechanical ingenuity, and having +the practical aid of the celebrated optician Tulley, he devised formulae +for the combination of lenses of crown glass with others of flint +glass, so adjusted that the refractive errors of one were corrected +or compensated by the other, with the result of producing lenses of +hitherto unequalled powers of definition; lenses capable of showing an +image highly magnified, yet relatively free from those distortions +and fringes of color that had heretofore been so disastrous to true +interpretation of magnified structures. + +Lister had begun his studies of the lens in 1824, but it was not until +1830 that he contributed to the Royal Society the famous paper detailing +his theories and experiments. Soon after this various continental +opticians who had long been working along similar lines took the matter +up, and their expositions, in particular that of Amici, introduced +the improved compound microscope to the attention of microscopists +everywhere. And it required but the most casual trial to convince the +experienced observers that a new implement of scientific research had +been placed in their hands which carried them a long step nearer +the observation of the intimate physical processes which lie at the +foundation of vital phenomena. For the physiologist this perfection of +the compound microscope had the same significance that the, discovery +of America had for the fifteenth-century geographers--it promised a +veritable world of utterly novel revelations. Nor was the fulfilment of +that promise long delayed. + +Indeed, so numerous and so important were the discoveries now made in +the realm of minute anatomy that the rise of histology to the rank of an +independent science may be said to date from this period. Hitherto, ever +since the discovery of magnifying-glasses, there had been here and there +a man, such as Leuwenhoek or Malpighi, gifted with exceptional vision, +and perhaps unusually happy in his conjectures, who made important +contributions to the knowledge of the minute structure of organic +tissues; but now of a sudden it became possible for the veriest tyro to +confirm or refute the laborious observations of these pioneers, while +the skilled observer could step easily beyond the barriers of vision +that hitherto were quite impassable. And so, naturally enough, the +physiologists of the fourth decade of the nineteenth century rushed +as eagerly into the new realm of the microscope as, for example, their +successors of to-day are exploring the realm of the X-ray. + +Lister himself, who had become an eager interrogator of the instrument +he had perfected, made many important discoveries, the most notable +being his final settlement of the long-mooted question as to the true +form of the red corpuscles of the human blood. In reality, as everybody +knows nowadays, these are biconcave disks, but owing to their peculiar +figure it is easily possible to misinterpret the appearances they +present when seen through a poor lens, and though Dr. Thomas Young and +various other observers had come very near the truth regarding them, +unanimity of opinion was possible only after the verdict of the +perfected microscope was given. + +These blood corpuscles are so infinitesimal in size that something like +five millions of them are found in each cubic millimetre of the blood, +yet they are isolated particles, each having, so to speak, its own +personality. This, of course, had been known to microscopists since the +days of the earliest lenses. It had been noticed, too, by here and +there an observer, that certain of the solid tissues seemed to present +something of a granular texture, as if they, too, in their ultimate +constitution, were made up of particles. And now, as better and better +lenses were constructed, this idea gained ground constantly, though +for a time no one saw its full significance. In the case of vegetable +tissues, indeed, the fact that little particles encased a membranous +covering, and called cells, are the ultimate visible units of structure +had long been known. But it was supposed that animal tissues differed +radically from this construction. The elementary particles of vegetables +"were regarded to a certain extent as individuals which composed the +entire plant, while, on the other hand, no such view was taken of the +elementary parts of animals." + + +ROBERT BROWN AND THE CELL NUCLEUS + +In the year 1833 a further insight into the nature of the ultimate +particles of plants was gained through the observation of the English +microscopist Robert Brown, who, in the course of his microscopic studies +of the epidermis of orchids, discovered in the cells "an opaque spot," +which he named the nucleus. Doubtless the same "spot" had been seen +often enough before by other observers, but Brown was the first to +recognize it as a component part of the vegetable cell and to give it a +name. + + +"I shall conclude my observations on Orchideae," said Brown, "with a +notice of some points of their general structure, which chiefly relate +to the cellular tissue. In each cell of the epidermis of a great part +of this family, especially of those with membranous leaves, a single +circular areola, generally somewhat more opaque than, the membrane of +the cell, is observable. This areola, which is more or less distinctly +granular, is slightly convex, and although it seems to be on the surface +is in reality covered by the outer lamina of the cell. There is no +regularity as to its place in the cell; it is not unfrequently, however, +central or nearly so. + +"As only one areola belongs to each cell, and as in many cases where it +exists in the common cells of the epidermis, it is also visible in the +cutaneous glands or stomata, and in these is always double--one being on +each side of the limb--it is highly probable that the cutaneous gland is +in all cases composed of two cells of peculiar form, the line of union +being the longitudinal axis of the disk or pore. + +"This areola, or nucleus of the cell as perhaps it might be termed, +is not confined to the epidermis, being also found, not only in the +pubescence of the surface, particularly when jointed, as in cypripedium, +but in many cases in the parenchyma or internal cells of the tissue, +especially when these are free from the deposition of granular matter. + +"In the compressed cells of the epidermis the nucleus is in a +corresponding degree flattened; but in the internal tissue it is often +nearly spherical, more or less firmly adhering to one of the walls, +and projecting into the cavity of the cell. In this state it may not +unfrequently be found in the substance of the column and in that of the +perianthium. + +"The nucleus is manifest also in the tissue of the stigma, where in +accordance with the compression of the utriculi, it has an intermediate +form, being neither so much flattened as in the epidermis nor so convex +as it is in the internal tissue of the column. + +"I may here remark that I am acquainted with one case of apparent +exception to the nucleus being solitary in each utriculus or +cell--namely, in Bletia Tankervilliae. In the utriculi of the stigma of +this plant, I have generally, though not always, found a second areola +apparently on the surface, and composed of much larger granules than the +ordinary nucleus, which is formed of very minute granular matter, and +seems to be deep seated. + +"Mr. Bauer has represented the tissue of the stigma, in the species of +Bletia, both before and, as he believes, after impregnation; and in the +latter state the utriculi are marked with from one to three areolae of +similar appearance. + +"The nucleus may even be supposed to exist in the pollen of this family. +In the early stages of its formation, at least a minute areola is of +ten visible in the simple grain, and in each of the constituent parts +of cells of the compound grain. But these areolae may perhaps rather be +considered as merely the points of production of the tubes. + +"This nucleus of the cell is not confined to orchideae, but is equally +manifest in many other monocotyledonous families; and I have even +found it, hitherto however in very few cases, in the epidermis of +dicotyledonous plants; though in this primary division it may perhaps +be said to exist in the early stages of development of the pollen. Among +monocotyledons, the orders in which it is most remarkable are Liliaceae, +Hemerocallideae, Asphodeleae, Irideae, and Commelineae. + +"In some plants belonging to this last-mentioned family, especially +in Tradascantia virginica, and several nearly related species, it is +uncommonly distinct, not in the epidermis and in the jointed hairs of +the filaments, but in the tissue of the stigma, in the cells of the +ovulum even before impregnation, and in all the stages of formation +of the grains of pollen, the evolution of which is so remarkable in +tradascantia. + +"The few indications of the presence of this nucleus, or areola, that I +have hitherto met with in the publications of botanists are chiefly in +some figures of epidermis, in the recent works of Meyen and Purkinje, +and in one case, in M. Adolphe Broigniart's memoir on the structure of +leaves. But so little importance seems to be attached to it that the +appearance is not always referred to in the explanations of the figures +in which it is represented. Mr. Bauer, however, who has also figured +it in the utriculi of the stigma of Bletia Tankervilliae has more +particularly noticed it, and seems to consider it as only visible after +impregnation."(2) + + +SCHLEIDEN AND SCHWANN AND THE CELL THEORY + +That this newly recognized structure must be important in the economy of +the cell was recognized by Brown himself, and by the celebrated German +Meyen, who dealt with it in his work on vegetable physiology, published +not long afterwards; but it remained for another German, the professor +of botany in the University of Jena, Dr. M. J. Schleiden, to bring the +nucleus to popular attention, and to assert its all-importance in the +economy of the cell. + +Schleiden freely acknowledged his indebtedness to Brown for first +knowledge of the nucleus, but he soon carried his studies of that +structure far beyond those of its discoverer. He came to believe that +the nucleus is really the most important portion of the cell, in that +it is the original structure from which the remainder of the cell is +developed. Hence he named it the cytoblast. He outlined his views in +an epochal paper published in Muller's Archives in 1838, under title of +"Beitrage zur Phytogenesis." This paper is in itself of value, yet the +most important outgrowth of Schleiden's observations of the nucleus did +not spring from his own labors, but from those of a friend to whom he +mentioned his discoveries the year previous to their publication. +This friend was Dr. Theodor Schwann, professor of physiology in the +University of Louvain. + +At the moment when these observations were communicated to him Schwann +was puzzling over certain details of animal histology which he could +not clearly explain. His great teacher, Johannes Muller, had called +attention to the strange resemblance to vegetable cells shown by certain +cells of the chorda dorsalis (the embryonic cord from which the spinal +column is developed), and Schwann himself had discovered a corresponding +similarity in the branchial cartilage of a tadpole. Then, too, the +researches of Friedrich Henle had shown that the particles that make up +the epidermis of animals are very cell-like in appearance. Indeed, the +cell-like character of certain animal tissues had come to be matter of +common note among students of minute anatomy. Schwann felt that this +similarity could not be mere coincidence, but he had gained no clew to +further insight until Schleiden called his attention to the nucleus. +Then at once he reasoned that if there really is the correspondence +between vegetable and animal tissues that he suspected, and if the +nucleus is so important in the vegetable cell as Schleiden believed, +the nucleus should also be found in the ultimate particles of animal +tissues. + +Schwann's researches soon showed the entire correctness of this +assumption. A closer study of animal tissues under the microscope +showed, particularly in the case of embryonic tissues, that "opaque +spots" such as Schleiden described are really to be found there +in abundance--forming, indeed, a most characteristic phase of the +structure. The location of these nuclei at comparatively regular +intervals suggested that they are found in definite compartments of the +tissue, as Schleiden had shown to be the case with vegetables; indeed, +the walls that separated such cell-like compartments one from another +were in some cases visible. Particularly was this found to be the case +with embryonic tissues, and the study of these soon convinced Schwann +that his original surmise had been correct, and that all animal tissues +are in their incipiency composed of particles not unlike the ultimate +particles of vegetables in short, of what the botanists termed cells. +Adopting this name, Schwann propounded what soon became famous as his +cell theory, under title of Mikroskopische Untersuchungen uber die +Ubereinstimmung in der Structur und dent Wachsthum der Thiere und +Pflanzen. So expeditious had been his work that this book was published +early in 1839, only a few months after the appearance of Schleiden's +paper. + +As the title suggests, the main idea that actuated Schwann was to unify +vegetable and animal tissues. Accepting cell-structure as the basis of +all vegetable tissues, he sought to show that the same is true of animal +tissues, all the seeming diversities of fibre being but the alteration +and development of what were originally simple cells. And by cell +Schwann meant, as did Schleiden also, what the word ordinarily +implies--a cavity walled in on all sides. He conceived that the ultimate +constituents of all tissues were really such minute cavities, the most +important part of which was the cell wall, with its associated nucleus. +He knew, indeed, that the cell might be filled with fluid contents, but +he regarded these as relatively subordinate in importance to the wall +itself. This, however, did not apply to the nucleus, which was supposed +to lie against the cell wall and in the beginning to generate it. +Subsequently the wall might grow so rapidly as to dissociate itself +from its contents, thus becoming a hollow bubble or true cell; but the +nucleus, as long as it lasted, was supposed to continue in contact +with the cell wall. Schleiden had even supposed the nucleus to be a +constituent part of the wall, sometimes lying enclosed between two +layers of its substance, and Schwann quoted this view with seeming +approval. Schwann believed, however, that in the mature cell the nucleus +ceased to be functional and disappeared. + +The main thesis as to the similarity of development of vegetable and +animal tissues and the cellular nature of the ultimate constitution +of both was supported by a mass of carefully gathered evidence which a +multitude of microscopists at once confirmed, so Schwann's work became +a classic almost from the moment of its publication. Of course various +other workers at once disputed Schwann's claim to priority of discovery, +in particular the English microscopist Valentin, who asserted, not +without some show of justice, that he was working closely along the same +lines. Put so, for that matter, were numerous others, as Henle, Turpin, +Du-mortier, Purkinje, and Muller, all of whom Schwann himself had +quoted. Moreover, there were various physiologists who earlier than +any of these had foreshadowed the cell theory--notably Kaspar Friedrich +Wolff, towards the close of the previous century, and Treviranus about +1807, But, as we have seen in so many other departments of science, it +is one thing to foreshadow a discovery, it is quite another to give +it full expression and make it germinal of other discoveries. And when +Schwann put forward the explicit claim that "there is one universal +principle of development for the elementary parts, of organisms, however +different, and this principle is the formation of cells," he enunciated +a doctrine which was for all practical purposes absolutely new and +opened up a novel field for the microscopist to enter. A most important +era in physiology dates from the publication of his book in 1839. + + +THE CELL THEORY ELABORATED + +That Schwann should have gone to embryonic tissues for the establishment +of his ideas was no doubt due very largely to the influence of the great +Russian Karl Ernst von Baer, who about ten years earlier had published +the first part of his celebrated work on embryology, and whose ideas +were rapidly gaining ground, thanks largely to the advocacy of a few +men, notably Johannes Muller, in Germany, and William B. Carpenter, in +England, and to the fact that the improved microscope had made minute +anatomy popular. Schwann's researches made it plain that the best +field for the study of the animal cell is here, and a host of explorers +entered the field. The result of their observations was, in the main, +to confirm the claims of Schwann as to the universal prevalence of the +cell. The long-current idea that animal tissues grow only as a sort +of deposit from the blood-vessels was now discarded, and the fact of +so-called plantlike growth of animal cells, for which Schwann contended, +was universally accepted. Yet the full measure of the affinity between +the two classes of cells was not for some time generally apprehended. + +Indeed, since the substance that composes the cell walls of plants is +manifestly very different from the limiting membrane of the animal cell, +it was natural, so long as the wall was considered the most essential +part of the structure, that the divergence between the two classes +of cells should seem very pronounced. And for a time this was the +conception of the matter that was uniformly accepted. But as time +went on many observers had their attention called to the peculiar +characteristics of the contents of the cell, and were led to ask +themselves whether these might not be more important than had been +supposed. In particular, Dr. Hugo von Mohl, professor of botany in the +University of Tubingen, in the course of his exhaustive studies of +the vegetable cell, was impressed with the peculiar and characteristic +appearance of the cell contents. He observed universally within the cell +"an opaque, viscid fluid, having granules intermingled in it," which +made up the main substance of the cell, and which particularly impressed +him because under certain conditions it could be seen to be actively in +motion, its parts separated into filamentous streams. + +Von Mohl called attention to the fact that this motion of the cell +contents had been observed as long ago as 1774 by Bonaventura Corti, +and rediscovered in 1807 by Treviranus, and that these observers had +described the phenomenon under the "most unsuitable name of 'rotation +of the cell sap.'" Von Mohl recognized that the streaming substance was +something quite different from sap. He asserted that the nucleus of the +cell lies within this substance and not attached to the cell wall as +Schleiden had contended. He saw, too, that the chlorophyl granules, +and all other of the cell contents, are incorporated with the "opaque, +viscid fluid," and in 1846 he had become so impressed with the +importance of this universal cell substance that he gave it the name +of protoplasm. Yet in so doing he had no intention of subordinating the +cell wall. The fact that Payen, in 1844, had demonstrated that the +cell walls of all vegetables, high or low, are composed largely of one +substance, cellulose, tended to strengthen the position of the cell wall +as the really essential structure, of which the protoplasmic contents +were only subsidiary products. + +Meantime, however, the students of animal histology were more and more +impressed with the seeming preponderance of cell contents over cell +walls in the tissues they studied. They, too, found the cell to be +filled with a viscid, slimy fluid capable of motion. To this Dujardin +gave the name of sarcode. Presently it came to be known, through the +labors of Kolliker, Nageli, Bischoff, and various others, that there are +numerous lower forms of animal life which seem to be composed of this +sarcode, without any cell wall whatever. The same thing seemed to be +true of certain cells of higher organisms, as the blood corpuscles. +Particularly in the case of cells that change their shape markedly, +moving about in consequence of the streaming of their sarcode, did it +seem certain that no cell wall is present, or that, if present, its role +must be insignificant. + +And so histologists came to question whether, after all, the cell +contents rather than the enclosing wall must not be the really essential +structure, and the weight of increasing observations finally left no +escape from the conclusion that such is really the case. But attention +being thus focalized on the cell contents, it was at once apparent +that there is a far closer similarity between the ultimate particles of +vegetables and those of animals than had been supposed. Cellulose and +animal membrane being now regarded as more by-products, the way was +clear for the recognition of the fact that vegetable protoplasm and +animal sarcode are marvellously similar in appearance and general +properties. The closer the observation the more striking seemed this +similarity; and finally, about 1860, it was demonstrated by Heinrich de +Bary and by Max Schultze that the two are to all intents and purposes +identical. Even earlier Remak had reached a similar conclusion, and +applied Von Mohl's word protoplasm to animal cell contents, and now this +application soon became universal. Thenceforth this protoplasm was +to assume the utmost importance in the physiological world, being +recognized as the universal "physical basis of life," vegetable and +animal alike. This amounted to the logical extension and culmination +of Schwann's doctrine as to the similarity of development of the two +animate kingdoms. Yet at the same time it was in effect the banishment +of the cell that Schwann had defined. The word cell was retained, it +is true, but it no longer signified a minute cavity. It now implied, +as Schultze defined it, "a small mass of protoplasm endowed with the +attributes of life." This definition was destined presently to meet with +yet another modification, as we shall see; but the conception of the +protoplasmic mass as the essential ultimate structure, which might or +might not surround itself with a protective covering, was a permanent +addition to physiological knowledge. The earlier idea had, in effect, +declared the shell the most important part of the egg; this developed +view assigned to the yolk its true position. + +In one other important regard the theory of Schleiden and Schwann now +became modified. This referred to the origin of the cell. Schwann had +regarded cell growth as a kind of crystallization, beginning with the +deposit of a nucleus about a granule in the intercellular substance--the +cytoblastema, as Schleiden called it. But Von Mohl, as early as 1835, +had called attention to the formation of new vegetable cells through the +division of a pre-existing cell. Ehrenberg, another high authority of +the time, contended that no such division occurs, and the matter was +still in dispute when Schleiden came forward with his discovery of +so-called free cell-formation within the parent cell, and this for a +long time diverted attention from the process of division which Von Mohl +had described. All manner of schemes of cell-formation were put forward +during the ensuing years by a multitude of observers, and gained +currency notwithstanding Von Mohl's reiterated contention that there +are really but two ways in which the formation of new cells takes +place--namely, "first, through division of older cells; secondly, +through the formation of secondary cells lying free in the cavity of a +cell." + +But gradually the researches of such accurate observers as Unger, +Nageli, Kolliker, Reichart, and Remak tended to confirm the opinion of +Von Mohl that cells spring only from cells, and finally Rudolf Virchow +brought the matter to demonstration about 1860. His Omnis cellula e +cellula became from that time one of the accepted data of physiology. +This was supplemented a little later by Fleming's Omnis nucleus e +nucleo, when still more refined methods of observation had shown that +the part of the cell which always first undergoes change preparatory to +new cell-formation is the all-essential nucleus. Thus the nucleus was +restored to the important position which Schwann and Schleiden had given +it, but with greatly altered significance. Instead of being a structure +generated de novo from non-cellular substance, and disappearing as soon +as its function of cell-formation was accomplished, the nucleus was now +known as the central and permanent feature of every cell, indestructible +while the cell lives, itself the division-product of a pre-existing +nucleus, and the parent, by division of its substance, of other +generations of nuclei. The word cell received a final definition as "a +small mass of protoplasm supplied with a nucleus." + +In this widened and culminating general view of the cell theory it +became clear that every animate organism, animal or vegetable, is but a +cluster of nucleated cells, all of which, in each individual case, are +the direct descendants of a single primordial cell of the ovum. In the +developed individuals of higher organisms the successive generations of +cells become marvellously diversified in form and in specific functions; +there is a wonderful division of labor, special functions being chiefly +relegated to definite groups of cells; but from first to last there is +no function developed that is not present, in a primitive way, in +every cell, however isolated; nor does the developed cell, however +specialized, ever forget altogether any one of its primordial functions +or capacities. All physiology, then, properly interpreted, becomes +merely a study of cellular activities; and the development of the cell +theory takes its place as the great central generalization in physiology +of the nineteenth century. Something of the later developments of this +theory we shall see in another connection. + + +ANIMAL CHEMISTRY + +Just at the time when the microscope was opening up the paths that +were to lead to the wonderful cell theory, another novel line of +interrogation of the living organism was being put forward by a +different set of observers. Two great schools of physiological chemistry +had arisen--one under guidance of Liebig and Wohler, in Germany, the +other dominated by the great French master Jean Baptiste Dumas. Liebig +had at one time contemplated the study of medicine, and Dumas had +achieved distinction in connection with Prevost, at Geneva, in the +field of pure physiology before he turned his attention especially to +chemistry. Both these masters, therefore, and Wohler as well, found +absorbing interest in those phases of chemistry that have to do with the +functions of living tissues; and it was largely through their efforts +and the labors of their followers that the prevalent idea that vital +processes are dominated by unique laws was discarded and physiology was +brought within the recognized province of the chemist. So at about +the time when the microscope had taught that the cell is the really +essential structure of the living organism, the chemists had come to +understand that every function of the organism is really the expression +of a chemical change--that each cell is, in short, a miniature chemical +laboratory. And it was this combined point of view of anatomist and +chemist, this union of hitherto dissociated forces, that made possible +the inroads into the unexplored fields of physiology that were effected +towards the middle of the nineteenth century. + +One of the first subjects reinvestigated and brought to proximal +solution was the long-mooted question of the digestion of foods. +Spallanzani and Hunter had shown in the previous century that digestion +is in some sort a solution of foods; but little advance was made upon +their work until 1824, when Prout detected the presence of hydrochloric +acid in the gastric juice. A decade later Sprott and Boyd detected +the existence of peculiar glands in the gastric mucous membrane; and +Cagniard la Tour and Schwann independently discovered that the really +active principle of the gastric juice is a substance which was named +pepsin, and which was shown by Schwann to be active in the presence of +hydrochloric acid. + +Almost coincidently, in 1836, it was discovered by Purkinje +and Pappenheim that another organ than the stomach--namely, the +pancreas--has a share in digestion, and in the course of the ensuing +decade it came to be known, through the efforts of Eberle, Valentin, +and Claude Bernard, that this organ is all-important in the digestion +of starchy and fatty foods. It was found, too, that the liver and the +intestinal glands have each an important share in the work of preparing +foods for absorption, as also has the saliva--that, in short, a +coalition of forces is necessary for the digestion of all ordinary foods +taken into the stomach. + +And the chemists soon discovered that in each one of the essential +digestive juices there is at least one substance having certain +resemblances to pepsin, though acting on different kinds of food. The +point of resemblance between all these essential digestive agents is +that each has the remarkable property of acting on relatively enormous +quantities of the substance which it can digest without itself being +destroyed or apparently even altered. In virtue of this strange +property, pepsin and the allied substances were spoken of as ferments, +but more recently it is customary to distinguish them from such +organized ferments as yeast by designating them enzymes. The isolation +of these enzymes, and an appreciation of their mode of action, mark a +long step towards the solution of the riddle of digestion, but it must +be added that we are still quite in the dark as to the real ultimate +nature of their strange activity. + +In a comprehensive view, the digestive organs, taken as a whole, are +a gateway between the outside world and the more intimate cells of the +organism. Another equally important gateway is furnished by the lungs, +and here also there was much obscurity about the exact method of +functioning at the time of the revival of physiological chemistry. That +oxygen is consumed and carbonic acid given off during respiration the +chemists of the age of Priestley and Lavoisier had indeed made clear, +but the mistaken notion prevailed that it was in the lungs themselves +that the important burning of fuel occurs, of which carbonic acid is a +chief product. But now that attention had been called to the importance +of the ultimate cell, this misconception could not long hold its ground, +and as early as 1842 Liebig, in the course of his studies of animal +heat, became convinced that it is not in the lungs, but in the ultimate +tissues to which they are tributary, that the true consumption of +fuel takes place. Reviving Lavoisier's idea, with modifications and +additions, Liebig contended, and in the face of opposition finally +demonstrated, that the source of animal heat is really the consumption +of the fuel taken in through the stomach and the lungs. He showed that +all the activities of life are really the product of energy liberated +solely through destructive processes, amounting, broadly speaking, to +combustion occurring in the ultimate cells of the organism. Here is his +argument: + + +LIEBIG ON ANIMAL HEAT + +"The oxygen taken into the system is taken out again in the same forms, +whether in summer or in winter; hence we expire more carbon in cold +weather, and when the barometer is high, than we do in warm weather; and +we must consume more or less carbon in our food in the same proportion; +in Sweden more than in Sicily; and in our more temperate climate a full +eighth more in winter than in summer. + +"Even when we consume equal weights of food in cold and warm countries, +infinite wisdom has so arranged that the articles of food in different +climates are most unequal in the proportion of carbon they contain. The +fruits on which the natives of the South prefer to feed do not in the +fresh state contain more than twelve per cent. of carbon, while the +blubber and train-oil used by the inhabitants of the arctic regions +contain from sixty-six to eighty per cent. of carbon. + +"It is no difficult matter, in warm climates, to study moderation in +eating, and men can bear hunger for a long time under the equator; but +cold and hunger united very soon exhaust the body. + +"The mutual action between the elements of the food and the oxygen +conveyed by the circulation of the blood to every part of the body is +the source of animal heat. + +"All living creatures whose existence depends on the absorption of +oxygen possess within themselves a source of heat independent of +surrounding objects. + +"This truth applies to all animals, and extends besides to the +germination of seeds, to the flowering of plants, and to the maturation +of fruits. It is only in those parts of the body to which arterial +blood, and with it the oxygen absorbed in respiration, is conveyed that +heat is produced. Hair, wool, or feathers do not possess an elevated +temperature. This high temperature of the animal body, or, as it may be +called, disengagement of heat, is uniformly and under all circumstances +the result of the combination of combustible substance with oxygen. + +"In whatever way carbon may combine with oxygen, the act of combination +cannot take place without the disengagement of heat. It is a matter of +indifference whether the combination takes place rapidly or slowly, at a +high or at a low temperature; the amount of heat liberated is a constant +quantity. The carbon of the food, which is converted into carbonic acid +within the body, must give out exactly as much heat as if it had been +directly burned in the air or in oxygen gas; the only difference is that +the amount of heat produced is diffused over unequal times. In oxygen +the combustion is more rapid and the heat more intense; in air it is +slower, the temperature is not so high, but it continues longer. + +"It is obvious that the amount of heat liberated must increase or +diminish with the amount of oxygen introduced in equal times by +respiration. Those animals which respire frequently, and consequently +consume much oxygen, possess a higher temperature than others which, +with a body of equal size to be heated, take into the system less +oxygen. The temperature of a child (102 degrees) is higher than that of +an adult (99.5 degrees). That of birds (104 to 105.4 degrees) is higher +than that of quadrupeds (98.5 to 100.4 degrees), or than that of fishes +or amphibia, whose proper temperature is from 3.7 to 2.6 degrees higher +than that of the medium in which they live. All animals, strictly +speaking, are warm-blooded; but in those only which possess lungs is the +temperature of the body independent of the surrounding medium. + +"The most trustworthy observations prove that in all climates, in the +temperate zones as well as at the equator or the poles, the temperature +of the body in man, and of what are commonly called warm-blooded +animals, is invariably the same; yet how different are the circumstances +in which they live. + +"The animal body is a heated mass, which bears the same relation to +surrounding objects as any other heated mass. It receives heat when the +surrounding objects are hotter, it loses heat when they are colder +than itself. We know that the rapidity of cooling increases with +the difference between the heated body and that of the surrounding +medium--that is, the colder the surrounding medium the shorter the time +required for the cooling of the heated body. How unequal, then, must be +the loss of heat of a man at Palermo, where the actual temperature is +nearly equal to that of the body, and in the polar regions, where the +external temperature is from 70 to 90 degrees lower. + +"Yet notwithstanding this extremely unequal loss of heat, experience +has shown that the blood of an inhabitant of the arctic circle has a +temperature as high as that of the native of the South, who lives in so +different a medium. This fact, when its true significance is perceived, +proves that the heat given off to the surrounding medium is restored +within the body with great rapidity. This compensation takes place more +rapidly in winter than in summer, at the pole than at the equator. + +"Now in different climates the quantity of oxygen introduced into the +system of respiration, as has been already shown, varies according to +the temperature of the external air; the quantity of inspired oxygen +increases with the loss of heat by external cooling, and the quantity +of carbon or hydrogen necessary to combine with this oxygen must be +increased in like ratio. It is evident that the supply of heat lost by +cooling is effected by the mutual action of the elements of the food and +the inspired oxygen, which combine together. To make use of a familiar, +but not on that account a less just illustration, the animal body acts, +in this respect, as a furnace, which we supply with fuel. It signifies +nothing what intermediate forms food may assume, what changes it may +undergo in the body, the last change is uniformly the conversion +of carbon into carbonic acid and of its hydrogen into water; the +unassimilated nitrogen of the food, along with the unburned or +unoxidized carbon, is expelled in the excretions. In order to keep up +in a furnace a constant temperature, we must vary the supply of fuel +according to the external temperature--that is, according to the supply +of oxygen. + +"In the animal body the food is the fuel; with a proper supply of oxygen +we obtain the heat given out during its oxidation or combustion."(3) + + +BLOOD CORPUSCLES, MUSCLES, AND GLANDS + +Further researches showed that the carriers of oxygen, from the time of +its absorption in the lungs till its liberation in the ultimate tissues, +are the red corpuscles, whose function had been supposed to be the +mechanical one of mixing of the blood. It transpired that the red +corpuscles are composed chiefly of a substance which Kuhne first +isolated in crystalline form in 1865, and which was named haemoglobin--a +substance which has a marvellous affinity for oxygen, seizing on it +eagerly at the lungs vet giving it up with equal readiness when coursing +among the remote cells of the body. When freighted with oxygen it +becomes oxyhaemoglobin and is red in color; when freed from its oxygen +it takes a purple hue; hence the widely different appearance of arterial +and venous blood, which so puzzled the early physiologists. + +This proof of the vitally important role played by the red-blood +corpuscles led, naturally, to renewed studies of these infinitesimal +bodies. It was found that they may vary greatly in number at different +periods in the life of the same individual, proving that they may be +both developed and destroyed in the adult organism. Indeed, extended +observations left no reason to doubt that the process of corpuscle +formation and destruction may be a perfectly normal one--that, in +short, every red-blood corpuscle runs its course and dies like any more +elaborate organism. They are formed constantly in the red marrow of +bones, and are destroyed in the liver, where they contribute to the +formation of the coloring matter of the bile. Whether there are other +seats of such manufacture and destruction of the corpuscles is not +yet fully determined. Nor are histologists agreed as to whether the +red-blood corpuscles themselves are to be regarded as true cells, or +merely as fragments of cells budded out from a true cell for a special +purpose; but in either case there is not the slightest doubt that the +chief function of the red corpuscle is to carry oxygen. + +If the oxygen is taken to the ultimate cells before combining with +the combustibles it is to consume, it goes without saying that these +combustibles themselves must be carried there also. Nor could it be in +doubt that the chiefest of these ultimate tissues, as regards, quantity +of fuel required, are the muscles. A general and comprehensive view +of the organism includes, then, digestive apparatus and lungs as the +channels of fuel-supply; blood and lymph channels as the transportation +system; and muscle cells, united into muscle fibres, as the consumption +furnaces, where fuel is burned and energy transformed and rendered +available for the purposes of the organism, supplemented by a set of +excretory organs, through which the waste products--the ashes--are +eliminated from the system. + +But there remain, broadly speaking, two other sets of organs whose size +demonstrates their importance in the economy of the organism, yet +whose functions are not accounted for in this synopsis. These are those +glandlike organs, such as the spleen, which have no ducts and produce no +visible secretions, and the nervous mechanism, whose central organs are +the brain and spinal cord. What offices do these sets of organs perform +in the great labor-specializing aggregation of cells which we call a +living organism? + +As regards the ductless glands, the first clew to their function was +given when the great Frenchman Claude Bernard (the man of whom +his admirers loved to say, "He is not a physiologist merely; he is +physiology itself") discovered what is spoken of as the glycogenic +function of the liver. The liver itself, indeed, is not a ductless +organ, but the quantity of its biliary output seems utterly +disproportionate to its enormous size, particularly when it is +considered that in the case of the human species the liver contains +normally about one-fifth of all the blood in the entire body. Bernard +discovered that the blood undergoes a change of composition in passing +through the liver. The liver cells (the peculiar forms of which had been +described by Purkinje, Henle, and Dutrochet about 1838) have the power +to convert certain of the substances that come to them into a starchlike +compound called glycogen, and to store this substance away till it +is needed by the organism. This capacity of the liver cells is quite +independent of the bile-making power of the same cells; hence the +discovery of this glycogenic function showed that an organ may have +more than one pronounced and important specific function. But its chief +importance was in giving a clew to those intermediate processes between +digestion and final assimilation that are now known to be of such vital +significance in the economy of the organism. + +In the forty odd years that have elapsed since this pioneer observation +of Bernard, numerous facts have come to light showing the extreme +importance of such intermediate alterations of food-supplies in the +blood as that performed by the liver. It has been shown that the +pancreas, the spleen, the thyroid gland, the suprarenal capsules +are absolutely essential, each in its own way, to the health of the +organism, through metabolic changes which they alone seem capable of +performing; and it is suspected that various other tissues, including +even the muscles themselves, have somewhat similar metabolic capacities +in addition to their recognized functions. But so extremely intricate is +the chemistry of the substances involved that in no single case has the +exact nature of the metabolisms wrought by these organs been fully made +out. Each is in its way a chemical laboratory indispensable to the +right conduct of the organism, but the precise nature of its operations +remains inscrutable. The vast importance of the operations of these +intermediate organs is unquestioned. + +A consideration of the functions of that other set of organs known +collectively as the nervous system is reserved for a later chapter. + + + + +VI. THEORIES OF ORGANIC EVOLUTION + +GOETHE AND THE METAMORPHOSIS OF PARTS + +When Coleridge said of Humphry Davy that he might have been the greatest +poet of his time had he not chosen rather to be the greatest chemist, it +is possible that the enthusiasm of the friend outweighed the caution of +the critic. But however that may be, it is beyond dispute that the man +who actually was the greatest poet of that time might easily have taken +the very highest rank as a scientist had not the muse distracted his +attention. Indeed, despite these distractions, Johann Wolfgang von +Goethe achieved successes in the field of pure science that would insure +permanent recognition for his name had he never written a stanza of +poetry. Such is the versatility that marks the highest genius. + +It was in 1790 that Goethe published the work that laid the foundations +of his scientific reputation--the work on the Metamorphoses of Plants, +in which he advanced the novel doctrine that all parts of the flower are +modified or metamorphosed leaves. + +"Every one who observes the growth of plants, even superficially," +wrote Goethe, "will notice that certain external parts of them become +transformed at times and go over into the forms of the contiguous parts, +now completely, now to a greater or less degree. Thus, for example, the +single flower is transformed into a double one when, instead of stamens, +petals are developed, which are either exactly like the other petals of +the corolla in form, and color or else still bear visible signs of their +origin. + +"When we observe that it is possible for a plant in this way to take a +step backward, we shall give so much the more heed to the regular course +of nature and learn the laws of transformation according to which she +produces one part through another, and displays the most varying forms +through the modification of one single organ. + +"Let us first direct our attention to the plant at the moment when it +develops out of the seed-kernel. The first organs of its upward +growth are known by the name of cotyledons; they have also been called +seed-leaves. + +"They often appear shapeless, filled with new matter, and are just as +thick as they are broad. Their vessels are unrecognizable and are hardly +to be distinguished from the mass of the whole; they bear almost no +resemblance to a leaf, and we could easily be misled into regarding them +as special organs. Occasionally, however, they appear as real leaves, +their vessels are capable of the most minute development, their +similarity to the following leaves does not permit us to take them for +special organs, but we recognize them instead to be the first leaves of +the stalk. + +"The cotyledons are mostly double, and there is an observation to be +made here which will appear still more important as we proceed--that +is, that the leaves of the first node are often paired, even when the +following leaves of the stalk stand alternately upon it. Here we see an +approximation and a joining of parts which nature afterwards separates +and places at a distance from one another. It is still more remarkable +when the cotyledons take the form of many little leaves gathered about +an axis, and the stalk which grows gradually from their midst produces +the following leaves arranged around it singly in a whorl. This may be +observed very exactly in the growth of the pinus species. Here a corolla +of needles forms at the same time a calyx, and we shall have occasion to +remember the present case in connection with similar phenomena later. + +"On the other hand, we observe that even the cotyledons which are most +like a leaf when compared with the following leaves of the stalk are +always more undeveloped or less developed. This is chiefly noticeable +in their margin which is extremely simple and shows few traces of +indentation. + +"A few or many of the next following leaves are often already present in +the seed, and lie enclosed between the cotyledons; in their folded state +they are known by the name of plumules. Their form, as compared with the +cotyledons and the following leaves, varies in different plants. Their +chief point of variance, however, from the cotyledons is that they are +flat, delicate, and formed like real leaves generally. They are wholly +green, rest on a visible node, and can no longer deny their relationship +to the following leaves of the stalk, to which, however, they are +usually still inferior, in so far as that their margin is not completely +developed. + +"The further development, however, goes on ceaselessly in the leaf, from +node to node; its midrib is elongated, and more or less additional ribs +stretch out from this towards the sides. The leaves now appear notched, +deeply indented, or composed of several small leaves, in which last case +they seem to form complete little branches. The date-palm furnishes a +striking example of such a successive transformation of the simplest +leaf form. A midrib is elongated through a succession of several +leaves, the single fan-shaped leaf becomes torn and diverted, and a very +complicated leaf is developed, which rivals a branch in form. + +"The transition to inflorescence takes place more or less rapidly. In +the latter case we usually observe that the leaves of the stalk loose +their different external divisions, and, on the other hand, spread out +more or less in their lower parts where they are attached to the stalk. +If the transition takes place rapidly, the stalk, suddenly become +thinner and more elongated since the node of the last-developed leaf, +shoots up and collects several leaves around an axis at its end. + +"That the petals of the calyx are precisely the same organs which have +hitherto appeared as leaves on the stalk, but now stand grouped about a +common centre in an often very different form, can, as it seems to me, +be most clearly demonstrated. Already in connection with the cotyledons +above, we noticed a similar working of nature. The first species, while +they are developing out of the seed-kernel, display a radiate crown of +unmistakable needles; and in the first childhood of these plants we see +already indicated that force of nature whereby when they are older their +flowering and fruit-giving state will be produced. + +"We see this force of nature, which collects several leaves around an +axis, produce a still closer union and make these approximated, modified +leaves still more unrecognizable by joining them together either +wholly or partially. The bell-shaped or so-called one-petalled calices +represent these cloudy connected leaves, which, being more or less +indented from above, or divided, plainly show their origin. + +"We can observe the transition from the calyx to the corolla in more +than one instance, for, although the color of the calyx is still usually +green, and like the color of the leaves of the stalk, it nevertheless +often varies in one or another of its parts--at the tips, the margins, +the back, or even, the inward side--while the outer still remains on +green. + +"The relationship of the corolla to the leaves of the stalk is shown +in more than one way, since on the stalks of some plants appear leaves +which are already more or less colored long before they approach +inflorescence; others are fully colored when near inflorescence. Nature +also goes over at once to the corolla, sometimes by skipping over the +organs of the calyx, and in such a case we likewise have an opportunity +to observe that leaves of the stalk become transformed into petals. Thus +on the stalk of tulips, for instance, there sometimes appears an almost +completely developed and colored petal. Even more remarkable is the +case when such a leaf, half green and half of it belonging to the stalk, +remains attached to the latter, while another colored part is raised +with the corolla, and the leaf is thus torn in two. + +"The relationship between the petals and stamens is very close. In some +instances nature makes the transition regular--e.g., among the Canna +and several plants of the same family. A true, little-modified petal is +drawn together on its upper margin, and produces a pollen sac, while the +rest of the petal takes the place of the stamen. In double flowers +we can observe this transition in all its stages. In several kinds of +roses, within the fully developed and colored petals there appear other +ones which are drawn together in the middle or on the side. This drawing +together is produced by a small weal, which appears as a more or less +complete pollen sac, and in the same proportion the leaf approaches the +simple form of a stamen. + +"The pistil in many cases looks almost like a stamen without anthers, +and the relationship between the formation of the two is much closer +than between the other parts. In retrograde fashion nature often +produces cases where the style and stigma (Narben) become retransformed +into petals--that is, the Ranunculus Asiaticus becomes double by +transforming the stigma and style of the fruit-receptacle into real +petals, while the stamens are often found unchanged immediately behind +the corolla. + +"In the seed receptacles, in spite of their formation, of their special +object, and of their method of being joined together, we cannot fail to +recognize the leaf form. Thus, for instance, the pod would be a simple +leaf folded and grown together on its margin; the siliqua would consist +of more leaves folded over another; the compound receptacles would be +explained as being several leaves which, being united above one centre, +keep their inward parts separate and are joined on their margins. We can +convince ourselves of this by actual sight when such composite capsules +fall apart after becoming ripe, because then every part displays an +opened pod."(1) + + +The theory thus elaborated of the metamorphosis of parts was presently +given greater generality through extension to the animal kingdom, in +the doctrine which Goethe and Oken advanced independently, that the +vertebrate skull is essentially a modified and developed vertebra. These +were conceptions worthy of a poet--impossible, indeed, for any mind that +had not the poetic faculty of correlation. But in this case the poet's +vision was prophetic of a future view of the most prosaic science. +The doctrine of metamorphosis of parts soon came to be regarded as of +fundamental importance. + +But the doctrine had implications that few of its early advocates +realized. If all the parts of a flower--sepal, petal, stamen, +pistil, with their countless deviations of contour and color--are +but modifications of the leaf, such modification implies a marvellous +differentiation and development. To assert that a stamen is a +metamorphosed leaf means, if it means anything, that in the long sweep +of time the leaf has by slow or sudden gradations changed its character +through successive generations, until the offspring, so to speak, of a +true leaf has become a stamen. But if such a metamorphosis as this +is possible--if the seemingly wide gap between leaf and stamen may +be spanned by the modification of a line of organisms--where does the +possibility of modification of organic type find its bounds? Why may +not the modification of parts go on along devious lines until the remote +descendants of an organism are utterly unlike that organism? Why may we +not thus account for the development of various species of beings all +sprung from one parent stock? That, too, is a poet's dream; but is it +only a dream? Goethe thought not. Out of his studies of metamorphosis of +parts there grew in his mind the belief that the multitudinous species +of plants and animals about us have been evolved from fewer and fewer +earlier parent types, like twigs of a giant tree drawing their nurture +from the same primal root. It was a bold and revolutionary thought, and +the world regarded it as but the vagary of a poet. + + +ERASMUS DARWIN + +Just at the time when this thought was taking form in Goethe's brain, +the same idea was germinating in the mind of another philosopher, an +Englishman of international fame, Dr. Erasmus Darwin, who, while he +lived, enjoyed the widest popularity as a poet, the rhymed couplets +of his Botanic Garden being quoted everywhere with admiration. And +posterity repudiating the verse which makes the body of the book, +yet grants permanent value to the book itself, because, forsooth, its +copious explanatory foot-notes furnish an outline of the status of +almost every department of science of the time. + +But even though he lacked the highest art of the versifier, Darwin had, +beyond peradventure, the imagination of a poet coupled with profound +scientific knowledge; and it was his poetic insight, correlating +organisms seemingly diverse in structure and imbuing the lowliest flower +with a vital personality, which led him to suspect that there are no +lines of demarcation in nature. "Can it be," he queries, "that one +form of organism has developed from another; that different species +are really but modified descendants of one parent stock?" The alluring +thought nestled in his mind and was nurtured there, and grew in a fixed +belief, which was given fuller expression in his Zoonomia and in the +posthumous Temple of Nature. + +Here is his rendering of the idea as versified in the Temple of Nature: + + "Organic life beneath the shoreless waves + Was born, and nursed in Ocean's pearly caves; + First forms minute, unseen by spheric glass, + Move on the mud, or pierce the watery mass; + These, as successive generations bloom, + New powers acquire and larger limbs assume; + Whence countless groups of vegetation spring, + And breathing realms of fin, and feet, and wing. + + "Thus the tall Oak, the giant of the wood, + Which bears Britannia's thunders on the flood; + The Whale, unmeasured monster of the main; + The lordly lion, monarch of the plain; + The eagle, soaring in the realms of air, + Whose eye, undazzled, drinks the solar glare; + Imperious man, who rules the bestial crowd, + Of language, reason, and reflection proud, + With brow erect, who scorns this earthy sod, + And styles himself the image of his God-- + Arose from rudiments of form and sense, + An embryon point or microscopic ens!"(2) + + +Here, clearly enough, is the idea of evolution. But in that day there +was little proof forthcoming of its validity that could satisfy any +one but a poet, and when Erasmus Darwin died, in 1802, the idea of +transmutation of species was still but an unsubstantiated dream. + +It was a dream, however, which was not confined to Goethe and Darwin. +Even earlier the idea had come more or less vaguely to another great +dreamer--and worker--of Germany, Immanuel Kant, and to several great +Frenchmen, including De Maillet, Maupertuis, Robinet, and the famous +naturalist Buffon--a man who had the imagination of a poet, though his +message was couched in most artistic prose. Not long after the middle of +the eighteenth century Buffon had put forward the idea of transmutation +of species, and he reiterated it from time to time from then on till +his death in 1788. But the time was not yet ripe for the idea of +transmutation of species to burst its bonds. + +And yet this idea, in a modified or undeveloped form, had taken strange +hold upon the generation that was upon the scene at the close of the +eighteenth century. Vast numbers of hitherto unknown species of animals +had been recently discovered in previously unexplored regions of the +globe, and the wise men were sorely puzzled to account for the disposal +of all of these at the time of the deluge. It simplified matters greatly +to suppose that many existing species had been developed since the +episode of the ark by modification of the original pairs. The remoter +bearings of such a theory were overlooked for the time, and the idea +that American animals and birds, for example, were modified descendants +of Old-World forms--the jaguar of the leopard, the puma of the lion, and +so on--became a current belief with that class of humanity who accept +almost any statement as true that harmonizes with their prejudices +without realizing its implications. + +Thus it is recorded with eclat that the discovery of the close proximity +of America at the northwest with Asia removes all difficulties as to the +origin of the Occidental faunas and floras, since Oriental species +might easily have found their way to America on the ice, and have been +modified as we find them by "the well-known influence of climate." And +the persons who gave expression to this idea never dreamed of its +real significance. In truth, here was the doctrine of evolution in a +nutshell, and, because its ultimate bearings were not clear, it seemed +the most natural of doctrines. But most of the persons who advanced it +would have turned from it aghast could they have realized its import. +As it was, however, only here and there a man like Buffon reasoned +far enough to inquire what might be the limits of such assumed +transmutation; and only here and there a Darwin or a Goethe reached the +conviction that there are no limits. + + +LAMARCK VERSUS CUVIER + +And even Goethe and Darwin had scarcely passed beyond that tentative +stage of conviction in which they held the thought of transmutation of +species as an ancillary belief not ready for full exposition. There was +one of their contemporaries, however, who, holding the same conception, +was moved to give it full explication. This was the friend and disciple +of Buffon, Jean Baptiste de Lamarck. Possessed of the spirit of a poet +and philosopher, this great Frenchman had also the widest range of +technical knowledge, covering the entire field of animate nature. The +first half of his long life was devoted chiefly to botany, in which he +attained high distinction. Then, just at the beginning of the nineteenth +century, he turned to zoology, in particular to the lower forms of +animal life. Studying these lowly organisms, existing and fossil, he +was more and more impressed with the gradations of form everywhere to be +seen; the linking of diverse families through intermediate ones; and +in particular with the predominance of low types of life in the earlier +geological strata. Called upon constantly to classify the various forms +of life in the course of his systematic writings, he found it more +and more difficult to draw sharp lines of demarcation, and at last the +suspicion long harbored grew into a settled conviction that there is +really no such thing as a species of organism in nature; that "species" +is a figment of the human imagination, whereas in nature there are only +individuals. + +That certain sets of individuals are more like one another than like +other sets is of course patent, but this only means, said Lamarck, that +these similar groups have had comparatively recent common ancestors, +while dissimilar sets of beings are more remotely related in +consanguinity. But trace back the lines of descent far enough, and all +will culminate in one original stock. All forms of life whatsoever are +modified descendants of an original organism. From lowest to highest, +then, there is but one race, one species, just as all the multitudinous +branches and twigs from one root are but one tree. For purposes of +convenience of description, we may divide organisms into orders, +families, genera, species, just as we divide a tree into root, trunk, +branches, twigs, leaves; but in the one case, as in the other, the +division is arbitrary and artificial. + +In Philosophie Zoologique (1809), Lamarck first explicitly formulated +his ideas as to the transmutation of species, though he had outlined +them as early as 1801. In this memorable publication not only did he +state his belief more explicitly and in fuller detail than the idea +had been expressed by any predecessor, but he took another long forward +step, carrying him far beyond all his forerunners except Darwin, in +that he made an attempt to explain the way in which the transmutation of +species had been brought about. The changes have been wrought, he said, +through the unceasing efforts of each organism to meet the needs imposed +upon it by its environment. Constant striving means the constant use +of certain organs. Thus a bird running by the seashore is constantly +tempted to wade deeper and deeper in pursuit of food; its incessant +efforts tend to develop its legs, in accordance with the observed +principle that the use of any organ tends to strengthen and develop it. +But such slightly increased development of the legs is transmitted to +the off spring of the bird, which in turn develops its already improved +legs by its individual efforts, and transmits the improved tendency. +Generation after generation this is repeated, until the sum of the +infinitesimal variations, all in the same direction, results in the +production of the long-legged wading-bird. In a similar way, through +individual effort and transmitted tendency, all the diversified organs +of all creatures have been developed--the fin of the fish, the wing of +the bird, the hand of man; nay, more, the fish itself, the bird, the +man, even. Collectively the organs make up the entire organism; and what +is true of the individual organs must be true also of their ensemble, +the living being. + +Whatever might be thought of Lamarck's explanation of the cause of +transmutation--which really was that already suggested by Erasmus +Darwin--the idea of the evolution for which he contended was but the +logical extension of the conception that American animals are the +modified and degenerated descendants of European animals. But people as +a rule are little prone to follow ideas to their logical conclusions, +and in this case the conclusions were so utterly opposed to the proximal +bearings of the idea that the whole thinking world repudiated them with +acclaim. The very persons who had most eagerly accepted the idea of +transmutation of European species into American species, and similar +limited variations through changed environment, because of the +relief thus given the otherwise overcrowded ark, were now foremost in +denouncing such an extension of the doctrine of transmutation as Lamarck +proposed. + +And, for that matter, the leaders of the scientific world were equally +antagonistic to the Lamarckian hypothesis. Cuvier in particular, once +the pupil of Lamarck, but now his colleague, and in authority more than +his peer, stood out against the transmutation doctrine with all his +force. He argued for the absolute fixity of species, bringing to bear +the resources of a mind which, as a mere repository of facts, perhaps +never was excelled. As a final and tangible proof of his position, +he brought forward the bodies of ibises that had been embalmed by the +ancient Egyptians, and showed by comparison that these do not differ in +the slightest particular from the ibises that visit the Nile to-day. + +Cuvier's reasoning has such great historical interest--being the +argument of the greatest opponent of evolution of that day--that we +quote it at some length. + +"The following objections," he says, "have already been started against +my conclusions. Why may not the presently existing races of mammiferous +land quadrupeds be mere modifications or varieties of those ancient +races which we now find in the fossil state, which modifications may +have been produced by change of climate and other local circumstances, +and since raised to the present excessive difference by the operations +of similar causes during a long period of ages? + +"This objection may appear strong to those who believe in the indefinite +possibility of change of form in organized bodies, and think that, +during a succession of ages and by alterations of habitudes, all the +species may change into one another, or one of them give birth to all +the rest. Yet to these persons the following answer may be given from +their own system: If the species have changed by degrees, as they +assume, we ought to find traces of this gradual modification. Thus, +between the palaeotherium and the species of our own day, we should be +able to discover some intermediate forms; and yet no such discovery +has ever been made. Since the bowels of the earth have not preserved +monuments of this strange genealogy, we have no right to conclude that +the ancient and now extinct species were as permanent in their forms +and characters as those which exist at present; or, at least, that the +catastrophe which destroyed them did not leave sufficient time for the +productions of the changes that are alleged to have taken place. + +"In order to reply to those naturalists who acknowledge that the +varieties of animals are restrained by nature within certain limits, +it would be necessary to examine how far these limits extend. This is +a very curious inquiry, and in itself exceedingly interesting under +a variety of relations, but has been hitherto very little attended +to.... + +"Wild animals which subsist upon herbage feel the influence of climate a +little more extensively, because there is added to it the influence +of food, both in regard to its abundance and its quality. Thus the +elephants of one forest are larger than those of another; their tusks +also grow somewhat longer in places where their food may happen to be +more favorable for the production of the substance of ivory. The same +may take place in regard to the horns of stags and reindeer. But let +us examine two elephants, the most dissimilar that can be conceived, +we shall not discover the smallest difference in the number and +articulations of the bones, the structure of the teeth, etc......... + +"Nature appears also to have guarded against the alterations of species +which might proceed from mixture of breeds by influencing the various +species of animals with mutual aversion from one another. Hence all +the cunning and all the force that man is able to exert is necessary +to accomplish such unions, even between species that have the nearest +resemblances. And when the mule breeds that are thus produced by these +forced conjunctions happen to be fruitful, which is seldom the case, +this fecundity never continues beyond a few generations, and would not +probably proceed so far without a continuance of the same cares which +excited it at first. Thus we never see in a wild state intermediate +productions between the hare and the rabbit, between the stag and the +doe, or between the marten and the weasel. But the power of man changes +this established order, and continues to produce all these intermixtures +of which the various species are susceptible, but which they would never +produce if left to themselves. + +"The degrees of these variations are proportional to the intensity of +the causes that produced them--namely, the slavery or subjection +under which those animals are to man. They do not proceed far in +half-domesticated species. In the cat, for example, a softer or harsher +fur, more brilliant or more varied colors, greater or less size--these +form the whole extent of variety in the species; the skeleton of the +cat of Angora differs in no regular and constant circumstances from the +wild-cat of Europe...." + +The most remarkable effects of the influence of man are produced upon +that animal which he has reduced most completely under subjection. Dogs +have been transported by mankind into every part of the world and have +submitted their action to his entire direction. Regulated in their +unions by the pleasure or caprice of their masters, the almost endless +varieties of dogs differ from one another in color, in length, and +abundance of hair, which is sometimes entirely wanting; in their natural +instincts; in size, which varies in measure as one to five, mounting in +some instances to more than a hundredfold in bulk; in the form of their +ears, noses, and tails; in the relative length of their legs; in the +progressive development of the brain, in several of the domesticated +varieties occasioning alterations even in the form of the head, some of +them having long, slender muzzles with a flat forehead, others having +short muzzles with a forehead convex, etc., insomuch that the apparent +difference between a mastiff and a water-spaniel and between a greyhound +and a pugdog are even more striking than between almost any of the wild +species of a genus........ + +It follows from these observations that animals have certain fixed and +natural characters which resist the effects of every kind of influence, +whether proceeding from natural causes or human interference; and we +have not the smallest reason to suspect that time has any more effect on +them than climate. + +"I am aware that some naturalists lay prodigious stress upon the +thousands which they can call into action by a dash of their pens. In +such matters, however, our only way of judging as to the effects which +may be produced by a long period of time is by multiplying, as it were, +such as are produced by a shorter time. With this view I have endeavored +to collect all the ancient documents respecting the forms of animals; +and there are none equal to those furnished by the Egyptians, both in +regard to their antiquity and abundance. They have not only left us +representatives of animals, but even their identical bodies embalmed and +preserved in the catacombs. + +"I have examined, with the greatest attention, the engraved figures of +quadrupeds and birds brought from Egypt to ancient Rome, and all these +figures, one with another, have a perfect resemblance to their intended +objects, such as they still are to-day. + +"From all these established facts, there does not seem to be the +smallest foundation for supposing that the new genera which I have +discovered or established among extraneous fossils, such as the +paleoetherium, anoplotherium, megalonyx, mastodon, pterodactylis, etc., +have ever been the sources of any of our present animals, which only +differ so far as they are influenced by time or climate. Even if it +should prove true, which I am far from believing to be the case, that +the fossil elephants, rhinoceroses, elks, and bears do not differ +further from the existing species of the same genera than the present +races of dogs differ among themselves, this would by no means be a +sufficient reason to conclude that they were of the same species; since +the races or varieties of dogs have been influenced by the trammels +of domesticity, which those other animals never did, and indeed never +could, experience."(3) + + +To Cuvier's argument from the fixity of Egyptian mummified birds and +animals, as above stated, Lamarck replied that this proved nothing +except that the ibis had become perfectly adapted to its Egyptian +surroundings in an early day, historically speaking, and that the +climatic and other conditions of the Nile Valley had not since then +changed. His theory, he alleged, provided for the stability of species +under fixed conditions quite as well as for transmutation under varying +conditions. + +But, needless to say, the popular verdict lay with Cuvier; talent won +for the time against genius, and Lamarck was looked upon as an impious +visionary. His faith never wavered, however. He believed that he had +gained a true insight into the processes of animate nature, and +he reiterated his hypotheses over and over, particularly in the +introduction to his Histoire Naturelle des Animaux sans Vertebres, in +1815, and in his Systeme des Connaissances Positives de l'Homme, in +1820. He lived on till 1829, respected as a naturalist, but almost +unrecognized as a prophet. + + +TENTATIVE ADVANCES + +While the names of Darwin and Goethe, and in particular that of Lamarck, +must always stand out in high relief in this generation as the exponents +of the idea of transmutation of species, there are a few others which +must not be altogether overlooked in this connection. Of these the +most conspicuous is that of Gottfried Reinhold Treviranus, a German +naturalist physician, professor of mathematics in the lyceum at Bremen. + +It was an interesting coincidence that Treviranus should have published +the first volume of his Biologie, oder Philosophie der lebenden Natur, +in which his views on the transmutation of species were expounded, in +1802, the same twelvemonth in which Lamarck's first exposition of the +same doctrine appeared in his Recherches sur l'Organisation des Corps +Vivants. It is singular, too, that Lamarck, in his Hydrogelogie of +the same date, should independently have suggested "biology" as an +appropriate word to express the general science of living things. It is +significant of the tendency of thought of the time that the need of +such a unifying word should have presented itself simultaneously to +independent thinkers in different countries. + +That same memorable year, Lorenz Oken, another philosophical naturalist, +professor in the University of Zurich, published the preliminary +outlines of his Philosophie der Natur, which, as developed through +later publications, outlined a theory of spontaneous generation and of +evolution of species. Thus it appears that this idea was germinating +in the minds of several of the ablest men of the time during the +first decade of our century. But the singular result of their various +explications was to give sudden check to that undercurrent of thought +which for some time had been setting towards this conception. As soon as +it was made clear whither the concession that animals may be changed +by their environment must logically trend, the recoil from the idea +was instantaneous and fervid. Then for a generation Cuvier was almost +absolutely dominant, and his verdict was generally considered final. + +There was, indeed, one naturalist of authority in France who had the +hardihood to stand out against Cuvier and his school, and who was in a +position to gain a hearing, though by no means to divide the following. +This was Etienne Geoffroy Saint-Hilaire, the famous author of the +Philosophie Anatomique, and for many years the colleague of Lamarck +at the Jardin des Plantes. Like Goethe, Geoffroy was pre-eminently an +anatomist, and, like the great German, he had early been impressed with +the resemblances between the analogous organs of different classes of +beings. He conceived the idea that an absolute unity of type prevails +throughout organic nature as regards each set of organs. Out of this +idea grew his gradually formed belief that similarity of structure might +imply identity of origin--that, in short, one species of animal might +have developed from another. + +Geoffroy's grasp of this idea of transmutation was by no means so +complete as that of Lamarck, and he seems never to have fully determined +in his own mind just what might be the limits of such development of +species. Certainly he nowhere includes all organic creatures in one line +of descent, as Lamarck had done; nevertheless, he held tenaciously to +the truth as he saw it, in open opposition to Cuvier, with whom he held +a memorable debate at the Academy of Sciences in 1830--the debate which +so aroused the interest and enthusiasm of Goethe, but which, in the +opinion of nearly every one else, resulted in crushing defeat for +Geoffrey, and brilliant, seemingly final, victory for the advocate of +special creation and the fixity of species. + +With that all ardent controversy over the subject seemed to end, and +for just a quarter of a century to come there was published but a +single argument for transmutation of species which attracted any general +attention whatever. This oasis in a desert generation was a little +book called Vestiges of the Natural History of Creation, which appeared +anonymously in England in 1844, and which passed through numerous +editions, and was the subject of no end of abusive and derisive comment. +This book, the authorship of which remained for forty years a secret, +is now conceded to have been the work of Robert Chambers, the well-known +English author and publisher. The book itself is remarkable as being an +avowed and unequivocal exposition of a general doctrine of evolution, +its view being as radical and comprehensive as that of Lamarck himself. +But it was a resume of earlier efforts rather than a new departure, to +say nothing of its technical shortcomings, which may best be illustrated +by a quotation. + +"The whole question," says Chambers, "stands thus: For the theory of +universal order--that is, order as presiding in both the origin and +administration of the world--we have the testimony of a vast number of +facts in nature, and this one in addition--that whatever is left from +the domain of ignorance, and made undoubted matter of science, forms a +new support to the same doctrine. The opposite view, once predominant, +has been shrinking for ages into lesser space, and now maintains a +footing only in a few departments of nature which happen to be less +liable than others to a clear investigation. The chief of these, if not +almost the only one, is the origin of the organic kingdoms. So long as +this remains obscure, the supernatural will have a certain hold upon +enlightened persons. Should it ever be cleared up in a way that leaves +no doubt of a natural origin of plants and animals, there must be a +complete revolution in the view which is generally taken of the relation +of the Father of our being. + +"This prepares the way for a few remarks on the present state of opinion +with regard to the origin of organic nature. The great difficulty here +is the apparent determinateness of species. These forms of life being +apparently unchangeable, or at least always showing a tendency to return +to the character from which they have diverged, the idea arises that +there can have been no progression from one to another; each must have +taken its special form, independently of other forms, directly from the +appointment of the Creator. The Edinburgh Review writer says, 'they were +created by the hand of God and adapted to the conditions of the period.' +Now it is, in the first place, not certain that species constantly +maintain a fixed character, for we have seen that what were long +considered as determinate species have been transmuted into others. +Passing, however, from this fact, as it is not generally received among +men of science, there remain some great difficulties in connection +with the idea of special creation. First we should have to suppose, as +pointed out in my former volume, a most startling diversity of plan +in the divine workings, a great general plan or system of law in the +leading events of world-making, and a plan of minute, nice operation, +and special attention in some of the mere details of the process. The +discrepancy between the two conceptions is surely overpowering, when we +allow ourselves to see the whole matter in a steady and rational light. +There is, also, the striking fact of an ascertained historical progress +of plants and animals in the order of their organization; marine and +cellular plants and invertebrated animals first, afterwards higher +examples of both. In an arbitrary system we had surely no reason to +expect mammals after reptiles; yet in this order they came. The writer +in the Edinburgh Review speaks of animals as coming in adaptation to +conditions, but this is only true in a limited sense. The groves which +formed the coal-beds might have been a fitting habitation for reptiles, +birds, and mammals, as such groves are at the present day; yet we see +none of the last of these classes and hardly any traces of the two first +at that period of the earth. Where the iguanodon lived the elephant +might have lived, but there was no elephant at that time. The sea of the +Lower Silurian era was capable of supporting fish, but no fish existed. +It hence forcibly appears that theatres of life must have remained +unserviceable, or in the possession of a tenantry inferior to what might +have enjoyed them, for many ages: there surely would have been no such +waste allowed in a system where Omnipotence was working upon the plan +of minute attention to specialities. The fact seems to denote that the +actual procedure of the peopling of the earth was one of a natural kind, +requiring a long space of time for its evolution. In this supposition +the long existence of land without land animals, and more particularly +without the noblest classes and orders, is only analogous to the fact, +not nearly enough present to the minds of a civilized people, that to +this day the bulk of the earth is a waste as far as man is concerned. + +"Another startling objection is in the infinite local variation of +organic forms. Did the vegetable and animal kingdoms consist of a +definite number of species adapted to peculiarities of soil and climate, +and universally distributed, the fact would be in harmony with the +idea of special exertion. But the truth is that various regions exhibit +variations altogether without apparent end or purpose. Professor Henslow +enumerates forty-five distinct flowers or sets of plants upon the +surface of the earth, notwithstanding that many of these would be +equally suitable elsewhere. The animals of different continents are +equally various, few species being the same in any two, though the +general character may conform. The inference at present drawn from this +fact is that there must have been, to use the language of the Rev. Dr. +Pye Smith, 'separate and original creations, perhaps at different and +respectively distinct epochs.' It seems hardly conceivable that rational +men should give an adherence to such a doctrine when we think of what it +involves. In the single fact that it necessitates a special fiat of the +inconceivable Author of this sand-cloud of worlds to produce the flora +of St. Helena, we read its more than sufficient condemnation. It surely +harmonizes far better with our general ideas of nature to suppose that, +just as all else in this far-spread science was formed on the laws +impressed upon it at first by its Author, so also was this. An exception +presented to us in such a light appears admissible only when we succeed +in forbidding our minds to follow out those reasoning processes to +which, by another law of the Almighty, they tend, and for which they are +adapted."(4) + + +Such reasoning as this naturally aroused bitter animadversions, and +cannot have been without effect in creating an undercurrent of thought +in opposition to the main trend of opinion of the time. But the book can +hardly be said to have done more than that. Indeed, some critics +have denied it even this merit. After its publication, as before, +the conception of transmutation of species remained in the popular +estimation, both lay and scientific, an almost forgotten "heresy." + +It is true that here and there a scientist of greater or less repute--as +Von Buch, Meckel, and Von Baer in Germany, Bory Saint-Vincent in +France, Wells, Grant, and Matthew in England, and Leidy in America--had +expressed more or less tentative dissent from the doctrine of +special creation and immutability of species, but their unaggressive +suggestions, usually put forward in obscure publications, and +incidentally, were utterly overlooked and ignored. And so, despite the +scientific advances along many lines at the middle of the century, the +idea of the transmutability of organic races had no such prominence, +either in scientific or unscientific circles, as it had acquired fifty +years before. Special creation held the day, seemingly unopposed. + + +DARWIN AND THE ORIGIN OF SPECIES + +But even at this time the fancied security of the special-creation +hypothesis was by no means real. Though it seemed so invincible, its +real position was that of an apparently impregnable fortress beneath +which, all unbeknown to the garrison, a powder-mine has been dug and +lies ready for explosion. For already there existed in the secluded +work-room of an English naturalist, a manuscript volume and a portfolio +of notes which might have sufficed, if given publicity, to shatter the +entire structure of the special-creation hypothesis. The naturalist who, +by dint of long and patient effort, had constructed this powder-mine of +facts was Charles Robert Darwin, grandson of the author of Zoonomia. + +As long ago as July 1, 1837, young Darwin, then twenty-eight years of +age, had opened a private journal, in which he purposed to record all +facts that came to him which seemed to have any bearing on the moot +point of the doctrine of transmutation of species. Four or five years +earlier, during the course of that famous trip around the world with +Admiral Fitzroy, as naturalist to the Beagle, Darwin had made the +personal observations which first tended to shake his belief of the +fixity of species. In South America, in the Pampean formation, he had +discovered "great fossil animals covered with armor like that on the +existing armadillos," and had been struck with this similarity of type +between ancient and existing faunas of the same region. He was also +greatly impressed by the manner in which closely related species of +animals were observed to replace one another as he proceeded southward +over the continent; and "by the South-American character of most of the +productions of the Galapagos Archipelago, and more especially by the +manner in which they differ slightly on each island of the group, none +of the islands appearing to be very ancient in a geological sense." + +At first the full force of these observations did not strike him; for, +under sway of Lyell's geological conceptions, he tentatively explained +the relative absence of life on one of the Galapagos Islands by +suggesting that perhaps no species had been created since that island +arose. But gradually it dawned upon him that such facts as he had +observed "could only be explained on the supposition that species +gradually become modified." From then on, as he afterwards asserted, the +subject haunted him; hence the journal of 1837. + +It will thus be seen that the idea of the variability of species came to +Charles Darwin as an inference from personal observations in the field, +not as a thought borrowed from books. He had, of course, read the works +of his grandfather much earlier in life, but the arguments of Zoonomia +and The Temple of Nature had not served in the least to weaken his +acceptance of the current belief in fixity of species. Nor had he been +more impressed with the doctrine of Lamarck, so closely similar to that +of his grandfather. Indeed, even after his South-American experience had +aroused him to a new point of view he was still unable to see anything +of value in these earlier attempts at an explanation of the variation +of species. In opening his journal, therefore, he had no preconceived +notion of upholding the views of these or any other makers of +hypotheses, nor at the time had he formulated any hypothesis of his own. +His mind was open and receptive; he was eager only for facts which might +lead him to an understanding of a problem which seemed utterly obscure. +It was something to feel sure that species have varied; but how have +such variations been brought about? + +It was not long before Darwin found a clew which he thought might +lead to the answer he sought. In casting about for facts he had soon +discovered that the most available field for observation lay among +domesticated animals, whose numerous variations within specific lines +are familiar to every one. Thus under domestication creatures so +tangibly different as a mastiff and a terrier have sprung from a +common stock. So have the Shetland pony, the thoroughbred, and the +draught-horse. In short, there is no domesticated animal that has not +developed varieties deviating more or less widely from the parent stock. +Now, how has this been accomplished? Why, clearly, by the preservation, +through selective breeding, of seemingly accidental variations. Thus +one horseman, by constantly selecting animals that "chance" to have +the right build and stamina, finally develops a race of running-horses; +while another horseman, by selecting a different series of progenitors, +has developed a race of slow, heavy draught animals. + +So far, so good; the preservation of "accidental" variations through +selective breeding is plainly a means by which races may be developed +that are very different from their original parent form. But this +is under man's supervision and direction. By what process could such +selection be brought about among creatures in a state of nature? Here +surely was a puzzle, and one that must be solved before another step +could be taken in this direction. + +The key to the solution of this puzzle came into Darwin's mind through +a chance reading of the famous essay on "Population" which Thomas +Robert Malthus had published almost half a century before. This +essay, expositing ideas by no means exclusively original with Malthus, +emphasizes the fact that organisms tend to increase at a geometrical +ratio through successive generations, and hence would overpopulate the +earth if not somehow kept in check. Cogitating this thought, Darwin +gained a new insight into the processes of nature. He saw that in virtue +of this tendency of each race of beings to overpopulate the earth, +the entire organic world, animal and vegetable, must be in a state of +perpetual carnage and strife, individual against individual, fighting +for sustenance and life. + +That idea fully imagined, it becomes plain that a selective influence +is all the time at work in nature, since only a few individuals, +relatively, of each generation can come to maturity, and these few +must, naturally, be those best fitted to battle with the particular +circumstances in the midst of which they are placed. In other words, the +individuals best adapted to their surroundings will, on the average, be +those that grow to maturity and produce offspring. To these +offspring will be transmitted the favorable peculiarities. Thus these +peculiarities will become permanent, and nature will have accomplished +precisely what the human breeder is seen to accomplish. Grant that +organisms in a state of nature vary, however slightly, one from another +(which is indubitable), and that such variations will be transmitted by +a parent to its offspring (which no one then doubted); grant, further, +that there is incessant strife among the various organisms, so that +only a small proportion can come to maturity--grant these things, said +Darwin, and we have an explanation of the preservation of variations +which leads on to the transmutation of species themselves. + +This wonderful coign of vantage Darwin had reached by 1839. Here was the +full outline of his theory; here were the ideas which afterwards came to +be embalmed in familiar speech in the phrases "spontaneous variation," +and the "survival of the fittest," through "natural selection." After +such a discovery any ordinary man would at once have run through the +streets of science, so to speak, screaming "Eureka!" Not so Darwin. He +placed the manuscript outline of his theory in his portfolio, and went +on gathering facts bearing on his discovery. In 1844 he made an abstract +in a manuscript book of the mass of facts by that time accumulated. +He showed it to his friend Hooker, made careful provision for its +publication in the event of his sudden death, then stored it away in +his desk and went ahead with the gathering of more data. This was the +unexploded powder-mine to which I have just referred. + +Twelve years more elapsed--years during which the silent worker gathered +a prodigious mass of facts, answered a multitude of objections that +arose in his own mind, vastly fortified his theory. All this time +the toiler was an invalid, never knowing a day free from illness and +discomfort, obliged to husband his strength, never able to work more +than an hour and a half at a stretch; yet he accomplished what would +have been vast achievements for half a dozen men of robust health. Two +friends among the eminent scientists of the day knew of his labors--Sir +Joseph Hooker, the botanist, and Sir Charles Lyell, the geologist. +Gradually Hooker had come to be more than half a convert to Darwin's +views. Lyell was still sceptical, yet he urged Darwin to publish his +theory without further delay lest he be forestalled. At last the patient +worker decided to comply with this advice, and in 1856 he set to work to +make another and fuller abstract of the mass of data he had gathered. + +And then a strange thing happened. After Darwin had been at work on his +"abstract" about two years, but before he had published a line of it, +there came to him one day a paper in manuscript, sent for his approval +by a naturalist friend named Alfred Russel Wallace, who had been for +some time at work in the East India Archipelago. He read the paper, and, +to his amazement, found that it contained an outline of the same theory +of "natural selection" which he himself had originated and for twenty +years had worked upon. Working independently, on opposite sides of the +globe, Darwin and Wallace had hit upon the same explanation of the cause +of transmutation of species. "Were Wallace's paper an abstract of my +unpublished manuscript of 1844," said Darwin, "it could not better +express my ideas." + +Here was a dilemma. To publish this paper with no word from Darwin would +give Wallace priority, and wrest from Darwin the credit of a discovery +which he had made years before his codiscoverer entered the field. Yet, +on the other hand, could Darwin honorably do otherwise than publish his +friend's paper and himself remain silent? It was a complication well +calculated to try a man's soul. Darwin's was equal to the test. Keenly +alive to the delicacy of the position, he placed the whole matter before +his friends Hooker and Lyell, and left the decision as to a course of +action absolutely to them. Needless to say, these great men did the one +thing which insured full justice to all concerned. They counselled a +joint publication, to include on the one hand Wallace's paper, and on +the other an abstract of Darwin's ideas, in the exact form in which it +had been outlined by the author in a letter to Asa Gray in the previous +year--an abstract which was in Gray's hands before Wallace's paper was +in existence. This joint production, together with a full statement of +the facts of the case, was presented to the Linnaean Society of London +by Hooker and Lyell on the evening of July 1, 1858, this being, by an +odd coincidence, the twenty-first anniversary of the day on which +Darwin had opened his journal to collect facts bearing on the "species +question." Not often before in the history of science has it happened +that a great theory has been nurtured in its author's brain through +infancy and adolescence to its full legal majority before being sent out +into the world. + +Thus the fuse that led to the great powder-mine had been lighted. The +explosion itself came more than a year later, in November, 1859, when +Darwin, after thirteen months of further effort, completed the outline +of his theory, which was at first begun as an abstract for the Linnaean +Society, but which grew to the size of an independent volume despite +his efforts at condensation, and which was given that ever-to-be-famous +title, The Origin of Species by Means of Natural Selection, or the +Preservation of Favored Races in the Struggle for Life. And what an +explosion it was! The joint paper of 1858 had made a momentary flare, +causing the hearers, as Hooker said, to "speak of it with bated breath," +but beyond that it made no sensation. What the result was when the +Origin itself appeared no one of our generation need be told. The rumble +and roar that it made in the intellectual world have not yet altogether +ceased to echo after more than forty years of reverberation. + + +NEW CHAMPIONS + +To the Origin of Species, then, and to its author, Charles Darwin, +must always be ascribed chief credit for that vast revolution in the +fundamental beliefs of our race which has come about since 1859, and +which made the second half of the century memorable. But it must not be +overlooked that no such sudden metamorphosis could have been effected +had it not been for the aid of a few notable lieutenants, who rallied +to the standards of the leader immediately after the publication of the +Origin. Darwin had all along felt the utmost confidence in the ultimate +triumph of his ideas. "Our posterity," he declared, in a letter to +Hooker, "will marvel as much about the current belief (in special +creation) as we do about fossil shells having been thought to be created +as we now see them." But he fully realized that for the present success +of his theory of transmutation the championship of a few leaders of +science was all-essential. He felt that if he could make converts of +Hooker and Lyell and of Thomas Henry Huxley at once, all would be well. + +His success in this regard, as in others, exceeded his expectations. +Hooker was an ardent disciple from reading the proof-sheets before the +book was published; Lyell renounced his former beliefs and fell into +line a few months later; while Huxley, so soon as he had mastered +the central idea of natural selection, marvelled that so simple yet +all-potent a thought had escaped him so long, and then rushed eagerly +into the fray, wielding the keenest dialectic blade that was drawn +during the entire controversy. Then, too, unexpected recruits were found +in Sir John Lubbock and John Tyndall, who carried the war eagerly into +their respective territories; while Herbert Spencer, who had advocated +a doctrine of transmutation on philosophic grounds some years before +Darwin published the key to the mystery--and who himself had barely +escaped independent discovery of that key--lent his masterful influence +to the cause. In America the famous botanist Asa Gray, who had long been +a correspondent of Darwin's but whose advocacy of the new theory had not +been anticipated, became an ardent propagandist; while in Germany Ernst +Heinrich Haeckel, the youthful but already noted zoologist, took up the +fight with equal enthusiasm. + +Against these few doughty champions--with here and there another of less +general renown--was arrayed, at the outset, practically all Christendom. +The interest of the question came home to every person of intelligence, +whatever his calling, and the more deeply as it became more and more +clear how far-reaching are the real bearings of the doctrine of natural +selection. Soon it was seen that should the doctrine of the survival +of the favored races through the struggle for existence win, there must +come with it as radical a change in man's estimate of his own position +as had come in the day when, through the efforts of Copernicus and +Galileo, the world was dethroned from its supposed central position in +the universe. The whole conservative majority of mankind recoiled from +this necessity with horror. And this conservative majority included not +laymen merely, but a vast preponderance of the leaders of science also. + +With the open-minded minority, on the other hand, the theory of +natural selection made its way by leaps and bounds. Its delightful +simplicity--which at first sight made it seem neither new nor +important--coupled with the marvellous comprehensiveness of its +implications, gave it a hold on the imagination, and secured it a +hearing where other theories of transmutation of species had been +utterly scorned. Men who had found Lamarck's conception of change +through voluntary effort ridiculous, and the vaporings of the Vestiges +altogether despicable, men whose scientific cautions held them back +from Spencer's deductive argument, took eager hold of that tangible, +ever-present principle of natural selection, and were led on and on to +its goal. Hour by hour the attitude of the thinking world towards this +new principle changed; never before was so great a revolution wrought so +suddenly. + +Nor was this merely because "the times were ripe" or "men's minds +prepared for evolution." Darwin himself bears witness that this was not +altogether so. All through the years in which he brooded this theory he +sounded his scientific friends, and could find among them not one +who acknowledged a doctrine of transmutation. The reaction from the +stand-point of Lamarck and Erasmus Darwin and Goethe had been complete, +and when Charles Darwin avowed his own conviction he expected always +to have it met with ridicule or contempt. In 1857 there was but one +man speaking with any large degree of authority in the world who openly +avowed a belief in transmutation of species--that man being Herbert +Spencer. But the Origin of Species came, as Huxley has said, like a +flash in the darkness, enabling the benighted voyager to see the way. +The score of years during which its author had waited and worked +had been years well spent. Darwin had become, as he himself says, a +veritable Croesus, "overwhelmed with his riches in facts"--facts of +zoology, of selective artificial breeding, of geographical distribution +of animals, of embryology, of paleontology. He had massed his facts +about his theory, condensed them and recondensed, until his volume of +five hundred pages was an encyclopaedia in scope. During those long +years of musing he had thought out almost every conceivable objection to +his theory, and in his book every such objection was stated with fullest +force and candor, together with such reply as the facts at command +might dictate. It was the force of those twenty years of effort of +a master-mind that made the sudden breach in the breaswtork{sic} of +current thought. + +Once this breach was effected the work of conquest went rapidly on. Day +by day squads of the enemy capitulated and struck their arms. By the +time another score of years had passed the doctrine of evolution had +become the working hypothesis of the scientific world. The revolution +had been effected. + +And from amid the wreckage of opinion and belief stands forth the figure +of Charles Darwin, calm, imperturbable, serene; scatheless to ridicule, +contumely, abuse; unspoiled by ultimate success; unsullied alike by +the strife and the victory--take him for all in all, for character, for +intellect, for what he was and what he did, perhaps the most Socratic +figure of the century. When, in 1882, he died, friend and foe alike +conceded that one of the greatest sons of men had rested from his +labors, and all the world felt it fitting that the remains of Charles +Darwin should be entombed in Westminster Abbey close beside the honored +grave of Isaac Newton. Nor were there many who would dispute the justice +of Huxley's estimate of his accomplishment: "He found a great truth +trodden under foot. Reviled by bigots, and ridiculed by all the world, +he lived long enough to see it, chiefly by his own efforts, irrefragably +established in science, inseparably incorporated with the common +thoughts of men, and only hated and feared by those who would revile but +dare not." + + +THE ORIGIN OF THE FITTEST + +Wide as are the implications of the great truth which Darwin and his +co-workers established, however, it leaves quite untouched the problem +of the origin of those "favored variations" upon which it operates. +That such variations are due to fixed and determinate causes no one +understood better than Darwin; but in his original exposition of his +doctrine he made no assumption as to what these causes are. He accepted +the observed fact of variation--as constantly witnessed, for example, in +the differences between parents and offspring--and went ahead from this +assumption. + +But as soon as the validity of the principle of natural selection came +to be acknowledged speculators began to search for the explanation of +those variations which, for purposes of argument, had been provisionally +called "spontaneous." Herbert Spencer had all along dwelt on this phase +of the subject, expounding the Lamarckian conceptions of the direct +influence of the environment (an idea which had especially appealed +to Buffon and to Geoffroy Saint-Hilaire), and of effort in response to +environment and stimulus as modifying the individual organism, and thus +supplying the basis for the operation of natural selection. Haeckel also +became an advocate of this idea, and presently there arose a so-called +school of neo-Lamarckians, which developed particular strength and +prominence in America under the leadership of Professors A. Hyatt and E. +D. Cope. + +But just as the tide of opinion was turning strongly in this direction, +an utterly unexpected obstacle appeared in the form of the theory of +Professor August Weismann, put forward in 1883, which antagonized the +Lamarckian conception (though not touching the Darwinian, of which +Weismann is a firm upholder) by denying that individual variations, +however acquired by the mature organism, are transmissible. The +flurry which this denial created has not yet altogether subsided, but +subsequent observations seem to show that it was quite disproportionate +to the real merits of the case. Notwithstanding Professor Weismann's +objections, the balance of evidence appears to favor the view that the +Lamarckian factor of acquired variations stands as the complement of the +Darwinian factor of natural selection in effecting the transmutation of +species. + +Even though this partial explanation of what Professor Cope calls the +"origin of the fittest" be accepted, there still remains one great life +problem which the doctrine of evolution does not touch. The origin +of species, genera, orders, and classes of beings through endless +transmutations is in a sense explained; but what of the first term of +this long series? Whence came that primordial organism whose transmuted +descendants make up the existing faunas and floras of the globe? + +There was a time, soon after the doctrine of evolution gained a hearing, +when the answer to that question seemed to some scientists of authority +to have been given by experiment. Recurring to a former belief, and +repeating some earlier experiments, the director of the Museum of +Natural History at Rouen, M. F. A. Pouchet, reached the conclusion that +organic beings are spontaneously generated about us constantly, in the +familiar processes of putrefaction, which were known to be due to the +agency of microscopic bacteria. But in 1862 Louis Pasteur proved that +this seeming spontaneous generation is in reality due to the existence +of germs in the air. Notwithstanding the conclusiveness of these +experiments, the claims of Pouchet were revived in England ten years +later by Professor Bastian; but then the experiments of John Tyndall, +fully corroborating the results of Pasteur, gave a final quietus to the +claim of "spontaneous generation" as hitherto formulated. + +There for the moment the matter rests. But the end is not yet. Fauna +and flora are here, and, thanks to Lamarck and Wallace and Darwin, their +development, through the operation of those "secondary causes" which we +call laws of nature, has been proximally explained. The lowest forms of +life have been linked with the highest in unbroken chains of descent. +Meantime, through the efforts of chemists and biologists, the gap +between the inorganic and the organic worlds, which once seemed almost +infinite, has been constantly narrowed. Already philosophy can throw +a bridge across that gap. But inductive science, which builds its own +bridges, has not yet spanned the chasm, small though it appear. Until +it shall have done so, the bridge of organic evolution is not quite +complete; yet even as it stands to-day it is perhaps the most stupendous +scientific structure of the nineteenth century. + + + + +VII. EIGHTEENTH-CENTURY MEDICINE + +THE SYSTEM OF BOERHAAVE + +At least two pupils of William Harvey distinguished themselves in +medicine, Giorgio Baglivi (1669-1707), who has been called the "Italian +Sydenham," and Hermann Boerhaave (1668-1738). The work of Baglivi was +hardly begun before his early death removed one of the most promising of +the early eighteenth-century physicians. Like Boerhaave, he represents a +type of skilled, practical clinitian rather than the abstract scientist. +One of his contributions to medical literature is the first accurate +description of typhoid, or, as he calls it, mesenteric fever. + +If for nothing else, Boerhaave must always be remembered as the teacher +of Von Haller, but in his own day he was the widest known and the most +popular teacher in the medical world. He was the idol of his pupils +at Leyden, who flocked to his lectures in such numbers that it became +necessary to "tear down the walls of Leyden to accommodate them." His +fame extended not only all over Europe but to Asia, North America, and +even into South America. A letter sent him from China was addressed +to "Boerhaave in Europe." His teachings represent the best medical +knowledge of his day, a high standard of morality, and a keen +appreciation of the value of observation; and it was through such +teachings imparted to his pupils and advanced by them, rather than to +any new discoveries, that his name is important in medical history. His +arrangement and classification of the different branches of medicine +are interesting as representing the attitude of the medical profession +towards these various branches at that time. + + +"In the first place we consider Life; then Health, afterwards Diseases; +and lastly their several Remedies. + +"Health the first general branch of Physic in our Institutions is termed +Physiology, or the Animal Oeconomy; demonstrating the several Parts of +the human Body, with their Mechanism and Actions. + +"The second branch of Physic is called Pathology, treating of Diseases, +their Differences, Causes and Effects, or Symptoms; by which the human +Body is known to vary from its healthy state. + +"The third part of Physic is termed Semiotica, which shows the Signs +distinguishing between sickness and Health, Diseases and their Causes +in the human Body; it also imports the State and Degrees of Health and +Diseases, and presages their future Events. + +"The fourth general branch of Physic is termed Hygiene, or Prophylaxis. + +"The fifth and last part of Physic is called Therapeutica; which +instructs us in the Nature, Preparation and uses of the Materia Medica; +and the methods of applying the same, in order to cure Diseases and +restore lost Health."(1) + +From this we may gather that his general view of medicine was not unlike +that taken at the present time. + +Boerhaave's doctrines were arranged into a "system" by Friedrich +Hoffmann, of Halle (1660-1742), this system having the merit of being +simple and more easily comprehended than many others. In this system +forces were considered inherent in matter, being expressed as mechanical +movements, and determined by mass, number, and weight. Similarly, forces +express themselves in the body by movement, contraction, and relaxation, +etc., and life itself is movement, "particularly movement of the +heart." Life and death are, therefore, mechanical phenomena, health is +determined by regularly recurring movements, and disease by irregularity +of them. The body is simply a large hydraulic machine, controlled by +"the aether" or "sensitive soul," and the chief centre of this soul lies +in the medulla. + +In the practical application of medicines to diseases Hoffman used +simple remedies, frequently with happy results, for whatever the +medical man's theory may be he seldom has the temerity to follow it out +logically, and use the remedies indicated by his theory to the exclusion +of long-established, although perhaps purely empirical, remedies. +Consequently, many vague theorists have been excellent practitioners, +and Hoffman was one of these. Some of the remedies he introduced are +still in use, notably the spirits of ether, or "Hoffman's anodyne." + + +ANIMISTS, VITALISTS, AND ORGANICISTS + +Besides Hoffman's system of medicine, there were numerous others during +the eighteenth century, most of which are of no importance whatever; +but three, at least, that came into existence and disappeared during the +century are worthy of fuller notice. One of these, the Animists, had for +its chief exponent Georg Ernst Stahl of "phlogiston" fame; another, the +Vitalists, was championed by Paul Joseph Barthez (1734-1806); and the +third was the Organicists. This last, while agreeing with the other +two that vital activity cannot be explained by the laws of physics +and chemistry, differed in not believing that life "was due to some +spiritual entity," but rather to the structure of the body itself. + +The Animists taught that the soul performed functions of ordinary life +in man, while the life of lower animals was controlled by ordinary +mechanical principles. Stahl supported this theory ardently, sometimes +violently, at times declaring that there were "no longer any doctors, +only mechanics and chemists." He denied that chemistry had anything to +do with medicine, and, in the main, discarded anatomy as useless to the +medical man. The soul, he thought, was the source of all vital movement; +and the immediate cause of death was not disease but the direct action +of the soul. When through some lesion, or because the machinery of the +body has become unworkable, as in old age, the soul leaves the body +and death is produced. The soul ordinarily selects the channels of the +circulation, and the contractile parts, as the route for influencing +the body. Hence in fever the pulse is quickened, due to the increased +activity of the soul, and convulsions and spasmodic movements in disease +are due, to the, same cause. Stagnation of the blood was supposed to +be a fertile cause of diseases, and such diseases were supposed to +arise mostly from "plethora"--an all-important element in Stahl's +therapeutics. By many this theory is regarded as an attempt on the +part of the pious Stahl to reconcile medicine and theology in a +way satisfactory to both physicians and theologians, but, like many +conciliatory attempts, it was violently opposed by both doctors and +ministers. + +A belief in such a theory would lead naturally to simplicity in +therapeutics, and in this respect at least Stahl was consistent. Since +the soul knew more about the body than any physician could know, Stahl +conceived that it would be a hinderance rather than a help for the +physician to interfere with complicated doses of medicine. As he +advanced in age this view of the administration of drugs grew upon him, +until after rejecting quinine, and finally opium, he at last used only +salt and water in treating his patients. From this last we may judge +that his "system," if not doing much good, was at least doing little +harm. + +The theory of the Vitalists was closely allied to that of the Animists, +and its most important representative, Paul Joseph Barthez, was a +cultured and eager scientist. After an eventful and varied career as +physician, soldier, editor, lawyer, and philosopher in turn, he finally +returned to the field of medicine, was made consulting physician by +Napoleon in 1802, and died in Paris four years later. + +The theory that he championed was based on the assumption that there was +a "vital principle," the nature of which was unknown, but which differed +from the thinking mind, and was the cause of the phenomena of life. This +"vital principle" differed from the soul, and was not exhibited in human +beings alone, but even in animals and plants. This force, or whatever it +might be called, was supposed to be present everywhere in the body, and +all diseases were the results of it. + +The theory of the Organicists, like that of the Animists and Vitalists, +agreed with the other two that vital activity could not be explained by +the laws of physics and chemistry, but, unlike them, it held that it +was a part of the structure of the body itself. Naturally the practical +physicians were more attracted by this tangible doctrine than by vague +theories "which converted diseases into unknown derangements of some +equally unknown 'principle.'" + +It is perhaps straining a point to include this brief description of +these three schools of medicine in the history of the progress of the +science. But, on the whole, they were negatively at least prominent +factors in directing true progress along its proper channel, showing +what courses were not to be pursued. Some one has said that science +usually stumbles into the right course only after stumbling into all +the wrong ones; and if this be only partially true, the wrong ones still +play a prominent if not a very creditable part. Thus the medical systems +of William Cullen (1710-1790), and John Brown (1735-1788), while doing +little towards the actual advancement of scientific medicine, played +so conspicuous a part in so wide a field that the "Brunonian system" at +least must be given some little attention. + +According to Brown's theory, life, diseases, and methods of cure are +explained by the property of "excitability." All exciting powers were +supposed to be stimulating, the apparent debilitating effects of some +being due to a deficiency in the amount of stimulus. Thus "the whole +phenomena of life, health, as well as disease, were supposed to consist +of stimulus and nothing else." This theory created a great stir in the +medical world, and partisans and opponents sprang up everywhere. In +Italy it was enthusiastically supported; in England it was strongly +opposed; while in Scotland riots took place between the opposing +factions. Just why this system should have created any stir, either for +or against it, is not now apparent. + +Like so many of the other "theorists" of his century, Brown's practical +conclusions deduced from his theory (or perhaps in spite of it) were +generally beneficial to medicine, and some of them extremely valuable in +the treatment of diseases. He first advocated the modern stimulant, or +"feeding treatment" of fevers, and first recognized the usefulness of +animal soups and beef-tea in certain diseases. + + +THE SYSTEM OF HAHNEMANN + +Just at the close of the century there came into prominence the school +of homoeopathy, which was destined to influence the practice of medicine +very materially and to outlive all the other eighteenth-century schools. +It was founded by Christian Samuel Friedrich Hahnemann (1755-1843), a +most remarkable man, who, after propounding a theory in his younger days +which was at least as reasonable as most of the existing theories, had +the misfortune to outlive his usefulness and lay his doctrine open to +ridicule by the unreasonable teachings of his dotage. + +Hahnemann rejected all the teachings of morbid anatomy and pathology +as useless in practice, and propounded his famous "similia similibus +curantur"--that all diseases were to be cured by medicine which in +health produced symptoms dynamically similar to the disease under +treatment. If a certain medicine produced a headache when given to a +healthy person, then this medicine was indicated in case of headaches, +etc. At the present time such a theory seems crude enough, but in the +latter part of the eighteenth century almost any theory was as good as +the ones propounded by Animists, Vitalists, and other such schools. It +certainly had the very commendable feature of introducing simplicity +in the use of drugs in place of the complicated prescriptions then in +vogue. Had Hahnemann stopped at this point he could not have been +held up to the indefensible ridicule that was brought upon him, with +considerable justice, by his later theories. But he lived onto propound +his extraordinary theory of "potentiality"--that medicines gained +strength by being diluted--and his even more extraordinary theory +that all chronic diseases are caused either by the itch, syphilis, or +fig-wart disease, or are brought on by medicines. + +At the time that his theory of potentialities was promulgated, the +medical world had gone mad in its administration of huge doses of +compound mixtures of drugs, and any reaction against this was surely +an improvement. In short, no medicine at all was much better than the +heaping doses used in common practice; and hence one advantage, at +least, of Hahnemann's methods. Stated briefly, his theory was that if a +tincture be reduced to one-fiftieth in strength, and this again reduced +to one-fiftieth, and this process repeated up to thirty such dilutions, +the potency of such a medicine will be increased by each dilution, +Hahnemann himself preferring the weakest, or, as he would call it, the +strongest dilution. The absurdity of such a theory is apparent when it +is understood that long before any drug has been raised to its thirtieth +dilution it has been so reduced in quantity that it cannot be weighed, +measured, or recognized as being present in the solution at all by +any means known to chemists. It is but just to modern followers of +homoeopathy to say that while most of them advocate small dosage, they +do not necessarily follow the teachings of Hahnemann in this respect, +believing that the theory of the dose "has nothing more to do with the +original law of cure than the psora (itch) theory has; and that it was +one of the later creations of Hahnemann's mind." + +Hahnemann's theory that all chronic diseases are derived from either +itch, syphilis, or fig-wart disease is no longer advocated by his +followers, because it is so easily disproved, particularly in the case +of itch. Hahnemann taught that fully three-quarters of all diseases were +caused by "itch struck in," and yet it had been demonstrated long before +his day, and can be demonstrated any time, that itch is simply a local +skin disease caused by a small parasite. + + +JENNER AND VACCINATION + +All advances in science have a bearing, near or remote, on the welfare +of our race; but it remains to credit to the closing decade of the +eighteenth century a discovery which, in its power of direct and +immediate benefit to humanity, surpasses any other discovery of this or +any previous epoch. Needless to say, I refer to Jenner's discovery +of the method of preventing smallpox by inoculation with the virus of +cow-pox. It detracts nothing from the merit of this discovery to say +that the preventive power of accidental inoculation had long been +rumored among the peasantry of England. Such vague, unavailing +half-knowledge is often the forerunner of fruitful discovery. + +To all intents and purposes Jenner's discovery was original and unique. +Nor, considered as a perfect method, was it in any sense an accident. It +was a triumph of experimental science. The discoverer was no novice in +scientific investigation, but a trained observer, who had served a long +apprenticeship in scientific observation under no less a scientist than +the celebrated John Hunter. At the age of twenty-one Jenner had gone to +London to pursue his medical studies, and soon after he proved himself +so worthy a pupil that for two years he remained a member of Hunter's +household as his favorite pupil. His taste for science and natural +history soon attracted the attention of Sir Joseph Banks, who intrusted +him with the preparation of the zoological specimens brought back by +Captain Cook's expedition in 1771. He performed this task so well that +he was offered the position of naturalist to the second expedition, but +declined it, preferring to take up the practice of his profession in his +native town of Berkeley. + +His many accomplishments and genial personality soon made him a favorite +both as a physician and in society. He was a good singer, a fair +violinist and flute-player, and a very successful writer of prose and +verse. But with all his professional and social duties he still kept up +his scientific investigations, among other things making some careful +observations on the hibernation of hedgehogs at the instigation of +Hunter, the results of which were laid before the Royal Society. He also +made quite extensive investigations as to the geological formations and +fossils found in his neighborhood. + +Even during his student days with Hunter he had been much interested in +the belief, current in the rural districts of Gloucestershire, of the +antagonism between cow-pox and small-pox, a person having suffered +from cow-pox being immuned to small-pox. At various times Jenner had +mentioned the subject to Hunter, and he was constantly making inquiries +of his fellow-practitioners as to their observations and opinions on the +subject. Hunter was too fully engrossed in other pursuits to give the +matter much serious attention, however, and Jenner's brothers of the +profession gave scant credence to the rumors, although such rumors were +common enough. + +At this time the practice of inoculation for preventing small-pox, or +rather averting the severer forms of the disease, was widely practised. +It was customary, when there was a mild case of the disease, to take +some of the virus from the patient and inoculate persons who had never +had the disease, producing a similar attack in them. Unfortunately there +were many objections to this practice. The inoculated patient frequently +developed a virulent form of the disease and died; or if he recovered, +even after a mild attack, he was likely to be "pitted" and disfigured. +But, perhaps worst of all, a patient so inoculated became the source of +infection to others, and it sometimes happened that disastrous epidemics +were thus brought about. The case was a most perplexing one, for the +awful scourge of small-pox hung perpetually over the head of every +person who had not already suffered and recovered from it. The practice +of inoculation was introduced into England by Lady Mary Wortley Montague +(1690-1762), who had seen it practised in the East, and who announced +her intention of "introducing it into England in spite of the doctors." + +From the fact that certain persons, usually milkmaids, who had suffered +from cow-pox seemed to be immuned to small-pox, it would seem a very +simple process of deduction to discover that cow-pox inoculation was the +solution of the problem of preventing the disease. But there was another +form of disease which, while closely resembling cow-pox and quite +generally confounded with it, did not produce immunity. The confusion of +these two forms of the disease had constantly misled investigations as +to the possibility of either of them immunizing against smallpox, and +the confusion of these two diseases for a time led Jenner to question +the possibility of doing so. After careful investigations, however, he +reached the conclusion that there was a difference in the effects of the +two diseases, only one of which produced immunity from small-pox. + +"There is a disease to which the horse, from his state of domestication, +is frequently subject," wrote Jenner, in his famous paper on +vaccination. "The farriers call it the grease. It is an inflammation and +swelling in the heel, accompanied at its commencement with small cracks +or fissures, from which issues a limpid fluid possessing properties of a +very peculiar kind. This fluid seems capable of generating a disease +in the human body (after it has undergone the modification I shall +presently speak of) which bears so strong a resemblance to small-pox +that I think it highly probable it may be the source of that disease. + +"In this dairy country a great number of cows are kept, and the office +of milking is performed indiscriminately by men and maid servants. One +of the former having been appointed to apply dressings to the heels of +a horse affected with the malady I have mentioned, and not paying due +attention to cleanliness, incautiously bears his part in milking the +cows with some particles of the infectious matter adhering to his +fingers. When this is the case it frequently happens that a disease is +communicated to the cows, and from the cows to the dairy-maids, which +spreads through the farm until most of the cattle and domestics feel its +unpleasant consequences. This disease has obtained the name of Cow-Pox. +It appears on the nipples of the cows in the form of irregular pustules. +At their first appearance they are commonly of a palish blue, or rather +of a color somewhat approaching to livid, and are surrounded by an +inflammation. These pustules, unless a timely remedy be applied, +frequently degenerate into phagedenic ulcers, which prove extremely +troublesome. The animals become indisposed, and the secretion of milk is +much lessened. Inflamed spots now begin to appear on different parts +of the hands of the domestics employed in milking, and sometimes on the +wrists, which run on to suppuration, first assuming the appearance of +the small vesications produced by a burn. Most commonly they appear +about the joints of the fingers and at their extremities; but whatever +parts are affected, if the situation will admit the superficial +suppurations put on a circular form with their edges more elevated than +their centre and of a color distinctly approaching to blue. Absorption +takes place, and tumors appear in each axilla. The system becomes +affected, the pulse is quickened; shiverings, succeeded by heat, general +lassitude, and pains about the loins and limbs, with vomiting, come on. +The head is painful, and the patient is now and then even affected +with delirium. These symptoms, varying in their degrees of violence, +generally continue from one day to three or four, leaving ulcerated +sores about the hands which, from the sensibility of the parts, are very +troublesome and commonly heal slowly, frequently becoming phagedenic, +like those from which they sprang. During the progress of the disease +the lips, nostrils, eyelids, and other parts of the body are sometimes +affected with sores; but these evidently arise from their being +heedlessly rubbed or scratched by the patient's infected fingers. No +eruptions on the skin have followed the decline of the feverish symptoms +in any instance that has come under my inspection, one only excepted, +and in this case a very few appeared on the arms: they were very +minute, of a vivid red color, and soon died away without advancing to +maturation, so that I cannot determine whether they had any connection +with the preceding symptoms. + +"Thus the disease makes its progress from the horse (as I conceive) to +the nipple of the cow, and from the cow to the human subject. + +"Morbid matter of various kinds, when absorbed into the system, may +produce effects in some degree similar; but what renders the cow-pox +virus so extremely singular is that the person that has been thus +affected is forever after secure from the infection of small-pox, +neither exposure to the variolous effluvia nor the insertion of the +matter into the skin producing this distemper."(2) + + +In 1796 Jenner made his first inoculation with cowpox matter, and two +months later the same subject was inoculated with small-pox matter. But, +as Jenner had predicted, no attack of small-pox followed. Although fully +convinced by this experiment that the case was conclusively proven, he +continued his investigations, waiting two years before publishing his +discovery. Then, fortified by indisputable proofs, he gave it to the +world. The immediate effects of his announcement have probably never +been equalled in the history of scientific discovery, unless, perhaps, +in the single instance of the discovery of anaesthesia. In Geneva and +Holland clergymen advocated the practice of vaccination from their +pulpits; in some of the Latin countries religious processions were +formed for receiving vaccination; Jenner's birthday was celebrated as +a feast in Germany; and the first child vaccinated in Russia was named +"Vaccinov" and educated at public expense. In six years the discovery +had penetrated to the most remote corners of civilization; it had even +reached some savage nations. And in a few years small-pox had fallen +from the position of the most dreaded of all diseases to that of being +practically the only disease for which a sure and easy preventive was +known. + +Honors were showered upon Jenner from the Old and the New World, and +even Napoleon, the bitter hater of the English, was among the others who +honored his name. On one occasion Jenner applied to the Emperor for the +release of certain Englishmen detained in France. The petition was about +to be rejected when the name of the petitioner was mentioned. "Ah," said +Napoleon, "we can refuse nothing to that name!" + +It is difficult for us of to-day clearly to conceive the greatness of +Jenner's triumph, for we can only vaguely realize what a ruthless and +ever-present scourge smallpox had been to all previous generations of +men since history began. Despite all efforts to check it by medication +and by direct inoculation, it swept now and then over the earth as an +all-devastating pestilence, and year by year it claimed one-tenth of +all the beings in Christendom by death as its average quota of victims. +"From small-pox and love but few remain free," ran the old saw. A pitted +face was almost as much a matter of course a hundred years ago as a +smooth one is to-day. + +Little wonder, then, that the world gave eager acceptance to Jenner's +discovery. No urging was needed to induce the majority to give it trial; +passengers on a burning ship do not hold aloof from the life-boats. Rich +and poor, high and low, sought succor in vaccination and blessed the +name of their deliverer. Of all the great names that were before the +world in the closing days of the century, there was perhaps no other one +at once so widely known and so uniformly reverenced as that of the great +English physician Edward Jenner. Surely there was no other one that +should be recalled with greater gratitude by posterity. + + + + +VIII. NINETEENTH-CENTURY MEDICINE + +PHYSICAL DIAGNOSIS + +Although Napoleon Bonaparte, First Consul, was not lacking in +self-appreciation, he probably did not realize that in selecting a +physician for his own needs he was markedly influencing the progress +of medical science as a whole. Yet so strangely are cause and effect +adjusted in human affairs that this simple act of the First Consul had +that very unexpected effect. For the man chosen was the envoy of a new +method in medical practice, and the fame which came to him through being +physician to the First Consul, and subsequently to the Emperor, enabled +him to promulgate the method in a way otherwise impracticable. Hence the +indirect but telling value to medical science of Napoleon's selection. + +The physician in question was Jean Nicolas de Corvisart. His novel +method was nothing more startling than the now-familiar procedure of +tapping the chest of a patient to elicit sounds indicative of diseased +tissues within. Every one has seen this done commonly enough in our day, +but at the beginning of the century Corvisart, and perhaps some of his +pupils, were probably the only physicians in the world who resorted to +this simple and useful procedure. Hence Napoleon's surprise when, on +calling in Corvisart, after becoming somewhat dissatisfied with +his other physicians Pinel and Portal, his physical condition was +interrogated in this strange manner. With characteristic shrewdness +Bonaparte saw the utility of the method, and the physician who thus +attempted to substitute scientific method for guess-work in the +diagnosis of disease at once found favor in his eyes and was installed +as his regular medical adviser. + +For fifteen years before this Corvisart had practised percussion, as +the chest-tapping method is called, without succeeding in convincing the +profession of its value. The method itself, it should be added, had not +originated with Corvisart, nor did the French physician for a moment +claim it as his own. The true originator of the practice was the German +physician Avenbrugger, who published a book about it as early as 1761. +This book had even been translated into French, then the language of +international communication everywhere, by Roziere de la Chassagne, of +Montpellier, in 1770; but no one other than Corvisart appears to +have paid any attention to either original or translation. It was far +otherwise, however, when Corvisart translated Avenbrugger's work anew, +with important additions of his own, in 1808. + +"I know very well how little reputation is allotted to translator and +commentators," writes Corvisart, "and I might easily have elevated +myself to the rank of an author if I had elaborated anew the doctrine +of Avenbrugger and published an independent work on percussion. In this +way, however, I should have sacrificed the name of Avenbrugger to my own +vanity, a thing which I am unwilling to do. It is he, and the beautiful +invention which of right belongs to him, that I desire to recall to +life."(1) + +By this time a reaction had set in against the metaphysical methods in +medicine that had previously been so alluring; the scientific spirit of +the time was making itself felt in medical practice; and this, combined +with Corvisart's fame, brought the method of percussion into immediate +and well-deserved popularity. Thus was laid the foundation for +the method of so-called physical diagnosis, which is one of the +corner-stones of modern medicine. + +The method of physical diagnosis as practised in our day was by no means +completed, however, with the work of Corvisart. Percussion alone tells +much less than half the story that may be elicited from the organs of +the chest by proper interrogation. The remainder of the story can +only be learned by applying the ear itself to the chest, directly or +indirectly. Simple as this seems, no one thought of practising it for +some years after Corvisart had shown the value of percussion. + +Then, in 1815, another Paris physician, Rene Theophile Hyacinthe +Laennec, discovered, almost by accident, that the sound of the +heart-beat could be heard surprisingly through a cylinder of paper held +to the ear and against the patient's chest. Acting on the hint thus +received, Laennec substituted a hollow cylinder of wood for the paper, +and found himself provided with an instrument through which not merely +heart sounds but murmurs of the lungs in respiration could be heard with +almost startling distinctness. + +The possibility of associating the varying chest sounds with diseased +conditions of the organs within appealed to the fertile mind of Laennec +as opening new vistas in therapeutics, which he determined to enter to +the fullest extent practicable. His connection with the hospitals of +Paris gave him full opportunity in this direction, and his labors of +the next few years served not merely to establish the value of the new +method as an aid to diagnosis, but laid the foundation also for the +science of morbid anatomy. In 1819 Laennec published the results of his +labors in a work called Traite d'Auscultation Mediate,(2) a work +which forms one of the landmarks of scientific medicine. By mediate +auscultation is meant, of course, the interrogation of the chest with +the aid of the little instrument already referred to, an instrument +which its originator thought hardly worth naming until various barbarous +appellations were applied to it by others, after which Laennec decided +to call it the stethoscope, a name which it has ever since retained. + +In subsequent years the form of the stethoscope, as usually employed, +was modified and its value augmented by a binauricular attachment, +and in very recent years a further improvement has been made through +application of the principle of the telephone; but the essentials of +auscultation with the stethoscope were established in much detail by +Laennec, and the honor must always be his of thus taking one of the +longest single steps by which practical medicine has in our century +acquired the right to be considered a rational science. Laennec's +efforts cost him his life, for he died in 1826 of a lung disease +acquired in the course of his hospital practice; but even before this +his fame was universal, and the value of his method had been recognized +all over the world. Not long after, in 1828, yet another French +physician, Piorry, perfected the method of percussion by introducing +the custom of tapping, not the chest directly, but the finger or a small +metal or hard-rubber plate held against the chest-mediate percussion, in +short. This perfected the methods of physical diagnosis of diseases of +the chest in all essentials; and from that day till this percussion +and auscultation have held an unquestioned place in the regular +armamentarium of the physician. + +Coupled with the new method of physical diagnosis in the effort to +substitute knowledge for guess-work came the studies of the experimental +physiologists--in particular, Marshall Hall in England and Francois +Magendie in France; and the joint efforts of these various workers +led presently to the abandonment of those severe and often irrational +depletive methods--blood-letting and the like--that had previously +dominated medical practice. To this end also the "statistical method," +introduced by Louis and his followers, largely contributed; and by the +close of the first third of our century the idea was gaining ground that +the province of therapeutics is to aid nature in combating disease, and +that this may often be accomplished better by simple means than by +the heroic measures hitherto thought necessary. In a word, scientific +empiricism was beginning to gain a hearing in medicine as against the +metaphysical preconceptions of the earlier generations. + + +PARASITIC DISEASES + +I have just adverted to the fact that Napoleon Bonaparte, as First +Consul and as Emperor, was the victim of a malady which caused him to +seek the advice of the most distinguished physicians of Paris. It is a +little shocking to modern sensibilities to read that these physicians, +except Corvisart, diagnosed the distinguished patient's malady as "gale +repercutee"--that is to say, in idiomatic English, the itch "struck in." +It is hardly necessary to say that no physician of today would make +so inconsiderate a diagnosis in the case of a royal patient. If by +any chance a distinguished patient were afflicted with the itch, the +sagacious physician would carefully hide the fact behind circumlocutions +and proceed to eradicate the disease with all despatch. That the +physicians of Napoleon did otherwise is evidence that at the beginning +of the century the disease in question enjoyed a very different status. +At that time itch, instead of being a most plebeian malady, was, so to +say, a court disease. It enjoyed a circulation, in high circles and in +low, that modern therapeutics has quite denied it; and the physicians +of the time gave it a fictitious added importance by ascribing to its +influence the existence of almost any obscure malady that came under +their observation. Long after Napoleon's time gale continued to hold +this proud distinction. For example, the imaginative Dr. Hahnemann did +not hesitate to affirm, as a positive maxim, that three-fourths of all +the ills that flesh is heir to were in reality nothing but various forms +of "gale repercutee." + +All of which goes to show how easy it may be for a masked pretender to +impose on credulous humanity, for nothing is more clearly established in +modern knowledge than the fact that "gale repercutee" was simply a name +to hide a profound ignorance; no such disease exists or ever did exist. +Gale itself is a sufficiently tangible reality, to be sure, but it is a +purely local disease of the skin, due to a perfectly definite cause, +and the dire internal conditions formerly ascribed to it have really no +causal connection with it whatever. This definite cause, as every one +nowadays knows, is nothing more or less than a microscopic insect which +has found lodgment on the skin, and has burrowed and made itself at home +there. Kill that insect and the disease is no more; hence it has come to +be an axiom with the modern physician that the itch is one of the three +or four diseases that he positively is able to cure, and that very +speedily. But it was far otherwise with the physicians of the first +third of our century, because to them the cause of the disease was an +absolute mystery. + +It is true that here and there a physician had claimed to find an insect +lodged in the skin of a sufferer from itch, and two or three times the +claim had been made that this was the cause of the malady, but such +views were quite ignored by the general profession, and in 1833 it was +stated in an authoritative medical treatise that the "cause of gale is +absolutely unknown." But even at this time, as it curiously happened, +there were certain ignorant laymen who had attained to a bit of medical +knowledge that was withheld from the inner circles of the profession. As +the peasantry of England before Jenner had known of the curative value +of cow-pox over small-pox, so the peasant women of Poland had learned +that the annoying skin disease from which they suffered was caused by +an almost invisible insect, and, furthermore, had acquired the trick of +dislodging the pestiferous little creature with the point of a needle. +From them a youth of the country, F. Renucci by name, learned the open +secret. He conveyed it to Paris when he went there to study medicine, +and in 1834 demonstrated it to his master Alibert. This physician, at +first sceptical, soon was convinced, and gave out the discovery to the +medical world with an authority that led to early acceptance. + +Now the importance of all this, in the present connection, is not at all +that it gave the clew to the method of cure of a single disease. What +makes the discovery epochal is the fact that it dropped a brand-new +idea into the medical ranks--an idea destined, in the long-run, to +prove itself a veritable bomb--the idea, namely, that a minute and quite +unsuspected animal parasite may be the cause of a well-known, widely +prevalent, and important human disease. Of course the full force of this +idea could only be appreciated in the light of later knowledge; but even +at the time of its coming it sufficed to give a great impetus to that +new medical knowledge, based on microscopical studies, which had but +recently been made accessible by the inventions of the lens-makers. The +new knowledge clarified one very turbid medical pool and pointed the way +to the clarification of many others. + +Almost at the same time that the Polish medical student was +demonstrating the itch mite in Paris, it chanced, curiously enough, +that another medical student, this time an Englishman, made an analogous +discovery of perhaps even greater importance. Indeed, this English +discovery in its initial stages slightly antedated the other, for it +was in 1833 that the student in question, James Paget, interne in St. +Bartholomew's Hospital, London, while dissecting the muscular tissues of +a human subject, found little specks of extraneous matter, which, +when taken to the professor of comparative anatomy, Richard Owen, were +ascertained, with the aid of the microscope, to be the cocoon of a +minute and hitherto unknown insect. Owen named the insect Trichina +spiralis. After the discovery was published it transpired that similar +specks had been observed by several earlier investigators, but no one +had previously suspected or, at any rate, demonstrated their nature. Nor +was the full story of the trichina made out for a long time after Owen's +discovery. It was not till 1847 that the American anatomist Dr. Joseph +Leidy found the cysts of trichina in the tissues of pork; and another +decade or so elapsed after that before German workers, chief among whom +were Leuckart, Virchow, and Zenker, proved that the parasite gets into +the human system through ingestion of infected pork, and that it causes +a definite set of symptoms of disease which hitherto had been mistaken +for rheumatism, typhoid fever, and other maladies. Then the medical +world was agog for a time over the subject of trichinosis; government +inspection of pork was established in some parts of Germany; American +pork was excluded altogether from France; and the whole subject thus +came prominently to public attention. But important as the trichina +parasite proved on its own account in the end, its greatest importance, +after all, was in the share it played in directing attention at the +time of its discovery in 1833 to the subject of microscopic parasites in +general. + +The decade that followed that discovery was a time of great activity in +the study of microscopic organisms and microscopic tissues, and such +men as Ehrenberg and Henle and Bory Saint-Vincent and Kolliker and +Rokitansky and Remak and Dujardin were widening the bounds of knowledge +of this new subject with details that cannot be more than referred to +here. But the crowning achievement of the period in this direction was +the discovery made by the German, J. L. Schoenlein, in 1839, that a very +common and most distressing disease of the scalp, known as favus, +is really due to the presence and growth on the scalp of a vegetable +organism of microscopic size. Thus it was made clear that not merely +animal but also vegetable organisms of obscure, microscopic species have +causal relations to the diseases with which mankind is afflicted. This +knowledge of the parasites was another long step in the direction of +scientific medical knowledge; but the heights to which this knowledge +led were not to be scaled, or even recognized, until another generation +of workers had entered the field. + + +PAINLESS SURGERY + +Meantime, in quite another field of medicine, events were developing +which led presently to a revelation of greater immediate importance to +humanity than any other discovery that had come in the century, +perhaps in any field of science whatever. This was the discovery of +the pain-dispelling power of the vapor of sulphuric ether inhaled by a +patient undergoing a surgical operation. This discovery came solely out +of America, and it stands curiously isolated, since apparently no minds +in any other country were trending towards it even vaguely. Davy, in +England, had indeed originated the method of medication by inhalation, +and earned out some most interesting experiments fifty years earlier, +and it was doubtless his experiments with nitrous oxide gas that gave +the clew to one of the American investigators; but this was the sole +contribution of preceding generations to the subject, and since the +beginning of the century, when Davy turned his attention to other +matters, no one had made the slightest advance along the same line until +an American dentist renewed the investigation. + +In view of the sequel, Davy's experiments merit full attention. Here is +his own account of them, as written in 1799: + + +"Immediately after a journey of one hundred and twenty-six miles, +in which I had no sleep the preceding night, being much exhausted, I +respired seven quarts of nitrous oxide gas for near three minutes. It +produced the usual pleasurable effects and slight muscular motion. I +continued exhilarated for some minutes afterwards, but in half an hour +found myself neither more nor less exhausted than before the experiment. +I had a great propensity to sleep. + +"To ascertain with certainty whether the more extensive action of +nitrous oxide compatible with life was capable of producing debility, I +resolved to breathe the gas for such a time, and in such quantities, +as to produce excitement equal in duration and superior in intensity to +that occasioned by high intoxication from opium or alcohol. + +"To habituate myself to the excitement, and to carry it on gradually, +on December 26th I was enclosed in an air-tight breathing-box, of the +capacity of about nine and one-half cubic feet, in the presence of Dr. +Kinglake. After I had taken a situation in which I could by means of a +curved thermometer inserted under the arm, and a stop-watch, ascertain +the alterations in my pulse and animal heat, twenty quarts of nitrous +oxide were thrown into the box. + +"For three minutes I experienced no alteration in my sensations, though +immediately after the introduction of the nitrous oxide the smell and +taste of it were very evident. In four minutes I began to feel a slight +glow in the cheeks and a generally diffused warmth over the chest, +though the temperature of the box was not quite 50 degrees.... In +twenty-five minutes the animal heat was 100 degrees, pulse 124. In +thirty minutes twenty quarts more of gas were introduced. + +"My sensations were now pleasant; I had a generally diffused warmth +without the slightest moisture of the skin, a sense of exhilaration +similar to that produced by a small dose of wine, and a disposition to +muscular motion and to merriment. + +"In three-quarters of an hour the pulse was 104 and the animal heat not +99.5 degrees, the temperature of the chamber 64 degrees. The pleasurable +feelings continued to increase, the pulse became fuller and slower, till +in about an hour it was 88, when the animal heat was 99 degrees. Twenty +quarts more of air were admitted. I had now a great disposition to +laugh, luminous points seemed frequently to pass before my eyes, my +hearing was certainly more acute, and I felt a pleasant lightness and +power of exertion in my muscles. In a short time the symptoms became +stationary; breathing was rather oppressed, and on account of the great +desire for action rest was painful. + +"I now came out of the box, having been in precisely an hour and a +quarter. The moment after I began to respire twenty quarts of unmingled +nitrous oxide. A thrilling extending from the chest to the extremities +was almost immediately produced. I felt a sense of tangible extension +highly pleasurable in every limb; my visible impressions were dazzling +and apparently magnified, I heard distinctly every sound in the room, +and was perfectly aware of my situation. By degrees, as the pleasurable +sensations increased, I lost all connection with external things; +trains of vivid visible images rapidly passed through my mind and +were connected with words in such a manner as to produce perceptions +perfectly novel. + +"I existed in a world of newly connected and newly modified ideas. I +theorized; I imagined that I made discoveries. When I was awakened from +this semi-delirious trance by Dr. Kinglake, who took the bag from my +mouth, indignation and pride were the first feelings produced by the +sight of persons about me. My emotions were enthusiastic and sublime; +and for a minute I walked about the room perfectly regardless of what +was said to me. As I recovered my former state of mind, I felt an +inclination to communicate the discoveries I had made during the +experiment. I endeavored to recall the ideas--they were feeble and +indistinct; one collection of terms, however, presented itself, and, +with most intense belief and prophetic manner, I exclaimed to Dr. +Kinglake, 'Nothing exists but thoughts!--the universe is composed of +impressions, ideas, pleasures, and pains.' "(3) + + +From this account we see that Davy has anaesthetized himself to a point +where consciousness of surroundings was lost, but not past the stage +of exhilaration. Had Dr. Kinglake allowed the inhaling-bag to remain in +Davy's mouth for a few moments longer complete insensibility would have +followed. As it was, Davy appears to have realized that sensibility was +dulled, for he adds this illuminative suggestion: "As nitrous oxide in +its extensive operation appears capable of destroying physical pain, it +may probably be used with advantage during surgical operations in which +no great effusion of blood takes place."(4) + +Unfortunately no one took advantage of this suggestion at the time, +and Davy himself became interested in other fields of science and never +returned to his physiological studies, thus barely missing one of the +greatest discoveries in the entire field of science. In the generation +that followed no one seems to have thought of putting Davy's suggestion +to the test, and the surgeons of Europe had acknowledged with one accord +that all hope of finding a means to render operations painless must be +utterly abandoned--that the surgeon's knife must ever remain a synonym +for slow and indescribable torture. By an odd coincidence it chanced +that Sir Benjamin Brodie, the acknowledged leader of English surgeons, +had publicly expressed this as his deliberate though regretted opinion +at a time when the quest which he considered futile had already led to +the most brilliant success in America, and while the announcement of +the discovery, which then had no transatlantic cable to convey it, was +actually on its way to the Old World. + +The American dentist just referred to, who was, with one exception to +be noted presently, the first man in the world to conceive that the +administration of a definite drug might render a surgical operation +painless and to give the belief application was Dr. Horace Wells, of +Hartford, Connecticut. The drug with which he experimented was nitrous +oxide--the same that Davy had used; the operation that he rendered +painless was no more important than the extraction of a tooth--yet it +sufficed to mark a principle; the year of the experiment was 1844. + +The experiments of Dr. Wells, however, though important, were not +sufficiently demonstrative to bring the matter prominently to the +attention of the medical world. The drug with which he experimented +proved not always reliable, and he himself seems ultimately to have +given the matter up, or at least to have relaxed his efforts. +But meantime a friend, to whom he had communicated his belief and +expectations, took the matter up, and with unremitting zeal carried +forward experiments that were destined to lead to more tangible results. +This friend was another dentist, Dr. W. T. G. Morton, of Boston, then a +young man full of youthful energy and enthusiasm. He seems to have +felt that the drug with which Wells had experimented was not the +most practicable one for the purpose, and so for several months +he experimented with other allied drugs, until finally he hit upon +sulphuric ether, and with this was able to make experiments upon +animals, and then upon patients in the dental chair, that seemed to him +absolutely demonstrative. + +Full of eager enthusiasm, and absolutely confident of his results, he at +once went to Dr. J. C. Warren, one of the foremost surgeons of Boston, +and asked permission to test his discovery decisively on one of the +patients at the Boston Hospital during a severe operation. The request +was granted; the test was made on October 16, 1846, in the presence of +several of the foremost surgeons of the city and of a body of medical +students. The patient slept quietly while the surgeon's knife was plied, +and awoke to astonished comprehension that the ordeal was over. The +impossible, the miraculous, had been accomplished.(5) + +Swiftly as steam could carry it--slowly enough we should think it +to-day--the news was heralded to all the world. It was received in +Europe with incredulity, which vanished before repeated experiments. +Surgeons were loath to believe that ether, a drug that had long held +a place in the subordinate armamentarium of the physician, could +accomplish such a miracle. But scepticism vanished before the tests +which any surgeon might make, and which surgeons all over the world did +make within the next few weeks. Then there came a lingering outcry from +a few surgeons, notably some of the Parisians, that the shock of pain +was beneficial to the patient, hence that anaesthesia--as Dr. Oliver +Wendell Holmes had christened the new method--was a procedure not to +be advised. Then, too, there came a hue-and-cry from many a pulpit that +pain was God-given, and hence, on moral grounds, to be clung to rather +than renounced. But the outcry of the antediluvians of both hospital +and pulpit quickly received its quietus; for soon it was clear that the +patient who did not suffer the shock of pain during an operation rallied +better than the one who did so suffer, while all humanity outside the +pulpit cried shame to the spirit that would doom mankind to suffer +needless agony. And so within a few months after that initial operation +at the Boston Hospital in 1846, ether had made good its conquest of +pain throughout the civilized world. Only by the most active use of the +imagination can we of this present day realize the full meaning of that +victory. + +It remains to be added that in the subsequent bickerings over the +discovery--such bickerings as follow every great advance--two other +names came into prominent notice as sharers in the glory of the new +method. Both these were Americans--the one, Dr. Charles T. Jackson, of +Boston; the other, Dr. Crawford W. Long, of Alabama. As to Dr. Jackson, +it is sufficient to say that he seems to have had some vague inkling +of the peculiar properties of ether before Morton's discovery. He even +suggested the use of this drug to Morton, not knowing that Morton had +already tried it; but this is the full measure of his association with +the discovery. Hence it is clear that Jackson's claim to equal share +with Morton in the discovery was unwarranted, not to say absurd. + +Dr. Long's association with the matter was far different and altogether +honorable. By one of those coincidences so common in the history +of discovery, he was experimenting with ether as a pain-destroyer +simultaneously with Morton, though neither so much as knew of the +existence of the other. While a medical student he had once inhaled +ether for the intoxicant effects, as other medical students were wont to +do, and when partially under influence of the drug he had noticed that a +chance blow to his shins was painless. This gave him the idea that ether +might be used in surgical operations; and in subsequent years, in the +course of his practice in a small Georgia town, he put the idea into +successful execution. There appears to be no doubt whatever that he +performed successful minor operations under ether some two or three +years before Morton's final demonstration; hence that the merit of first +using the drug, or indeed any drug, in this way belongs to him. But, +unfortunately, Dr. Long did not quite trust the evidence of his own +experiments. Just at that time the medical journals were full of +accounts of experiments in which painless operations were said to be +performed through practice of hypnotism, and Dr. Long feared that his +own success might be due to an incidental hypnotic influence rather than +to the drug. Hence he delayed announcing his apparent discovery until +he should have opportunity for further tests--and opportunities did not +come every day to the country practitioner. And while he waited, Morton +anticipated him, and the discovery was made known to the world without +his aid. It was a true scientific caution that actuated Dr. Long to this +delay, but the caution cost him the credit, which might otherwise have +been his, of giving to the world one of the greatest blessings--dare we +not, perhaps, say the very greatest?--that science has ever conferred +upon humanity. + +A few months after the use of ether became general, the Scotch surgeon +Sir J. Y. Simpson(6) discovered that another drug, chloroform, could be +administered with similar effects; that it would, indeed, in many cases +produce anaesthesia more advantageously even than ether. From that day +till this surgeons have been more or less divided in opinion as to +the relative merits of the two drugs; but this fact, of course, has no +bearing whatever upon the merit of the first discovery of the method of +anaesthesia. Even had some other drug subsequently quite banished ether, +the honor of the discovery of the beneficent method of anaesthesia would +have been in no wise invalidated. And despite all cavillings, it is +unequivocally established that the man who gave that method to the world +was William T. G. Morton. + + +PASTEUR AND THE GERM THEORY OF DISEASE + +The discovery of the anaesthetic power of drugs was destined presently, +in addition to its direct beneficences, to aid greatly in the progress +of scientific medicine, by facilitating those experimental studies +of animals from which, before the day of anaesthesia, many humane +physicians were withheld, and which in recent years have led to +discoveries of such inestimable value to humanity. But for the moment +this possibility was quite overshadowed by the direct benefits of +anaesthesia, and the long strides that were taken in scientific medicine +during the first fifteen years after Morton's discovery were mainly +independent of such aid. These steps were taken, indeed, in a field +that at first glance might seem to have a very slight connection with +medicine. Moreover, the chief worker in the field was not himself a +physician. He was a chemist, and the work in which he was now engaged +was the study of alcoholic fermentation in vinous liquors. Yet these +studies paved the way for the most important advances that medicine has +made in any century towards the plane of true science; and to this man +more than to any other single individual--it might almost be said more +than to all other individuals--was due this wonderful advance. It is +almost superfluous to add that the name of this marvellous chemist was +Louis Pasteur. + +The studies of fermentation which Pasteur entered upon in 1854 were +aimed at the solution of a controversy that had been waging in the +scientific world with varying degrees of activity for a quarter of a +century. Back in the thirties, in the day of the early enthusiasm over +the perfected microscope, there had arisen a new interest in the minute +forms of life which Leeuwenhoek and some of the other early workers with +the lens had first described, and which now were shown to be of almost +universal prevalence. These minute organisms had been studied more or +less by a host of observers, but in particular by the Frenchman Cagniard +Latour and the German of cell-theory fame, Theodor Schwann. These men, +working independently, had reached the conclusion, about 1837, that +the micro-organisms play a vastly more important role in the economy +of nature than any one previously had supposed. They held, for example, +that the minute specks which largely make up the substance of yeast are +living vegetable organisms, and that the growth of these organisms is +the cause of the important and familiar process of fermentation. They +even came to hold, at least tentatively, the opinion that the somewhat +similar micro-organisms to be found in all putrefying matter, animal or +vegetable, had a causal relation to the process of putrefaction. + +This view, particularly as to the nature of putrefaction, was expressed +even more outspokenly a little later by the French botanist Turpin. +Views so supported naturally gained a following; it was equally natural +that so radical an innovation should be antagonized. In this case it +chanced that one of the most dominating scientific minds of the time, +that of Liebig, took a firm and aggressive stand against the new +doctrine. In 1839 he promulgated his famous doctrine of fermentation, +in which he stood out firmly against any "vitalistic" explanation of the +phenomena, alleging that the presence of micro-organisms in fermenting +and putrefying substances was merely incidental, and in no sense causal. +This opinion of the great German chemist was in a measure substantiated +by experiments of his compatriot Helmholtz, whose earlier experiments +confirmed, but later ones contradicted, the observations of Schwann, and +this combined authority gave the vitalistic conception a blow from which +it had not rallied at the time when Pasteur entered the field. Indeed, +it was currently regarded as settled that the early students of the +subject had vastly over-estimated the importance of micro-organisms. + +And so it came as a new revelation to the generality of scientists +of the time, when, in 1857 and the succeeding half-decade, Pasteur +published the results of his researches, in which the question had been +put to a series of altogether new tests, and brought to unequivocal +demonstration. + +He proved that the micro-organisms do all that his most imaginative +predecessors had suspected, and more. Without them, he proved, there +would be no fermentation, no putrefaction--no decay of any tissues, +except by the slow process of oxidation. It is the microscopic +yeast-plant which, by seizing on certain atoms of the molecule, +liberates the remaining atoms in the form of carbonic-acid and alcohol, +thus effecting fermentation; it is another microscopic plant--a +bacterium, as Devaine had christened it--which in a similar way effects +the destruction of organic molecules, producing the condition which we +call putrefaction. Pasteur showed, to the amazement of biologists, that +there are certain forms of these bacteria which secure the oxygen which +all organic life requires, not from the air, but by breaking up unstable +molecules in which oxygen is combined; that putrefaction, in short, has +its foundation in the activities of these so-called anaerobic bacteria. + +In a word, Pasteur showed that all the many familiar processes of the +decay of organic tissues are, in effect, forms of fermentation, and +would not take place at all except for the presence of the living +micro-organisms. A piece of meat, for example, suspended in an +atmosphere free from germs, will dry up gradually, without the slightest +sign of putrefaction, regardless of the temperature or other conditions +to which it may have been subjected. Let us witness one or two series of +these experiments as presented by Pasteur himself in one of his numerous +papers before the Academy of Sciences. + + +EXPERIMENTS WITH GRAPE SUGAR + +"In the course of the discussion which took place before the Academy +upon the subject of the generation of ferments properly so-called, there +was a good deal said about that of wine, the oldest fermentation known. +On this account I decided to disprove the theory of M. Fremy by a +decisive experiment bearing solely upon the juice of grapes. + +"I prepared forty flasks of a capacity of from two hundred and fifty to +three hundred cubic centimetres and filled them half full with filtered +grape-must, perfectly clear, and which, as is the case of all acidulated +liquids that have been boiled for a few seconds, remains uncontaminated +although the curved neck of the flask containing them remain constantly +open during several months or years. + +"In a small quantity of water I washed a part of a bunch of grapes, the +grapes and the stalks together, and the stalks separately. This +washing was easily done by means of a small badger's-hair brush. The +washing-water collected the dust upon the surface of the grapes and the +stalks, and it was easily shown under the microscope that this water +held in suspension a multitude of minute organisms closely resembling +either fungoid spores, or those of alcoholic Yeast, or those of +Mycoderma vini, etc. This being done, ten of the forty flasks were +preserved for reference; in ten of the remainder, through the straight +tube attached to each, some drops of the washing-water were introduced; +in a third series of ten flasks a few drops of the same liquid were +placed after it had been boiled; and, finally, in the ten remaining +flasks were placed some drops of grape-juice taken from the inside of a +perfect fruit. In order to carry out this experiment, the straight tube +of each flask was drawn out into a fine and firm point in the lamp, and +then curved. This fine and closed point was filed round near the end and +inserted into the grape while resting upon some hard substance. When +the point was felt to touch the support of the grape it was by a slight +pressure broken off at the point file mark. Then, if care had been taken +to create a slight vacuum in the flask, a drop of the juice of the grape +got into it, the filed point was withdrawn, and the aperture immediately +closed in the alcohol lamp. This decreased pressure of the atmosphere in +the flask was obtained by the following means: After warming the sides +of the flask either in the hands or in the lamp-flame, thus causing a +small quantity of air to be driven out of the end of the curved neck, +this end was closed in the lamp. After the flask was cooled, there was +a tendency to suck in the drop of grape-juice in the manner just +described. + +"The drop of grape-juice which enters into the flask by this suction +ordinarily remains in the curved part of the tube, so that to mix it +with the must it was necessary to incline the flask so as to bring +the must into contact with the juice and then replace the flask in its +normal position. The four series of comparative experiments produced the +following results: + +"The first ten flasks containing the grape-must boiled in pure air did +not show the production of any organism. The grape-must could possibly +remain in them for an indefinite number of years. Those in the second +series, containing the water in which the grapes had been washed +separately and together, showed without exception an alcoholic +fermentation which in several cases began to appear at the end of +forty-eight hours when the experiment took place at ordinary summer +temperature. At the same time that the yeast appeared, in the form of +white traces, which little by little united themselves in the form of a +deposit on the sides of all the flasks, there were seen to form little +flakes of Mycellium, often as a single fungoid growth or in combination, +these fungoid growths being quite independent of the must or of any +alcoholic yeast. Often, also, the Mycoderma vini appeared after some +days upon the surface of the liquid. The Vibria and the lactic ferments +properly so called did not appear on account of the nature of the +liquid. + +"The third series of flasks, the washing-water in which had been +previously boiled, remained unchanged, as in the first series. Those of +the fourth series, in which was the juice of the interior of the grapes, +remained equally free from change, although I was not always able, on +account of the delicacy of the experiment, to eliminate every chance of +error. These experiments cannot leave the least doubt in the mind as to +the following facts: + +"Grape-must, after heating, never ferments on contact with the air, when +the air has been deprived of the germs which it ordinarily holds in a +state of suspension. + +"The boiled grape-must ferments when there is introduced into it a very +small quantity of water in which the surface of the grapes or their +stalks have been washed. + +"The grape-must does not ferment when this washing-water has been boiled +and afterwards cooled. + +"The grape-must does not ferment when there is added to it a small +quantity of the juice of the inside of the grape. + +"The yeast, therefore, which causes the fermentation of the grapes in +the vintage-tub comes from the outside and not from the inside of the +grapes. Thus is destroyed the hypothesis of MM. Trecol and Fremy, who +surmised that the albuminous matter transformed itself into yeast +on account of the vital germs which were natural to it. With greater +reason, therefore, there is no longer any question of the theory of +Liebig of the transformation of albuminoid matter into ferments on +account of the oxidation." + + +FOREIGN ORGANISMS AND THE WORT OF BEER + +"The method which I have just followed," Pasteur continues, "in order +to show that there exists a correlation between the diseases of beer and +certain microscopic organisms leaves no room for doubt, it seems to me, +in regard to the principles I am expounding. + +"Every time that the microscope reveals in the leaven, and especially in +the active yeast, the production of organisms foreign to the alcoholic +yeast properly so called, the flavor of the beer leaves something to be +desired, much or little, according to the abundance and the character of +these little germs. Moreover, when a finished beer of good quality loses +after a time its agreeable flavor and becomes sour, it can be easily +shown that the alcoholic yeast deposited in the bottles or the casks, +although originally pure, at least in appearance, is found to be +contaminated gradually with these filiform or other ferments. All +this can be deduced from the facts already given, but some critics may +perhaps declare that these foreign ferments are the consequences of the +diseased condition, itself produced by unknown causes. + +"Although this gratuitous hypothesis may be difficult to uphold, I will +endeavor to corroborate the preceding observations by a clearer method +of investigation. This consists in showing that the beer never has any +unpleasant taste in all cases when the alcoholic ferment properly so +called is not mixed with foreign ferments; that it is the same in +the case of wort, and that wort, liable to changes as it is, can be +preserved unaltered if it is kept from those microscopic parasites which +find in it a suitable nourishment and a field for growth. + +"The employment of this second method has, moreover, the advantage of +proving with certainty the proposition that I advanced at first--namely, +that the germs of these organisms are derived from the dust of the +atmosphere, carried about and deposited upon all objects, or scattered +over the utensils and the materials used in a brewery-materials +naturally charged with microscopic germs, and which the various +operations in the store-rooms and the malt-house may multiply +indefinitely. + +"Let us take a glass flask with a long neck of from two hundred and +fifty to three hundred cubic centimetres capacity, and place in it some +wort, with or without hops, and then in the flame of a lamp draw out the +neck of the flask to a fine point, afterwards heating the liquid until +the steam comes out of the end of the neck. It can then be allowed to +cool without any other precautions; but for additional safety there +can be introduced into the little point a small wad of asbestos at the +moment that the flame is withdrawn from beneath the flask. Before thus +placing the asbestos it also can be passed through the flame, as well as +after it has been put into the end of the tube. The air which then first +re-enters the flask will thus come into contact with the heated glass +and the heated liquid, so as to destroy the vitality of any dust germs +that may exist in the air. The air itself will re-enter very gradually, +and slowly enough to enable any dust to be taken up by the drop of water +which the air forces up the curvature of the tube. Ultimately the tube +will be dry, but the re-entering of the air will be so slow that the +particles of dust will fall upon the sides of the tube. The experiments +show that with this kind of vessel, allowing free communication with the +air, and the dust not being allowed to enter, the dust will not enter +at all events for a period of ten or twelve years, which has been the +longest period devoted to these trials; and the liquid, if it were +naturally limpid, will not be in the least polluted neither on its +surface nor in its mass, although the outside of the flask may become +thickly coated with dust. This is a most irrefutable proof of the +impossibility of dust getting inside the flask. + +"The wort thus prepared remains uncontaminated indefinitely, in spite +of its susceptibility to change when exposed to the air under conditions +which allow it to gather the dusty particles which float in the +atmosphere. It is the same in the case of urine, beef-tea, and +grape-must, and generally with all those putrefactable and fermentable +liquids which have the property when heated to boiling-point of +destroying the vitality of dust germs."(7) + + +There was nothing in these studies bearing directly upon the question +of animal diseases, yet before they were finished they had stimulated +progress in more than one field of pathology. At the very outset +they sufficed to start afresh the inquiry as to the role played by +micro-organisms in disease. In particular they led the French physician +Devaine to return to some interrupted studies which he had made ten +years before in reference to the animal disease called anthrax, or +splenic fever, a disease that cost the farmers of Europe millions of +francs annually through loss of sheep and cattle. In 1850 Devaine had +seen multitudes of bacteria in the blood of animals who had died of +anthrax, but he did not at that time think of them as having a causal +relation to the disease. Now, however, in 1863, stimulated by Pasteur's +new revelations regarding the power of bacteria, he returned to the +subject, and soon became convinced, through experiments by means of +inoculation, that the microscopic organisms he had discovered were the +veritable and the sole cause of the infectious disease anthrax. + +The publication of this belief in 1863 aroused a furor of controversy. +That a microscopic vegetable could cause a virulent systemic disease +was an idea altogether too startling to be accepted in a day, and the +generality of biologists and physicians demanded more convincing proofs +than Devaine as yet was able to offer. + +Naturally a host of other investigators all over the world entered the +field. Foremost among these was the German Dr. Robert Koch, who soon +corroborated all that Devaine had observed, and carried the experiments +further in the direction of the cultivation of successive generations of +the bacteria in artificial media, inoculations being made from such +pure cultures of the eighth generation, with the astonishing result that +animals thus inoculated succumbed to the disease. + +Such experiments seem demonstrative, yet the world was unconvinced, +and in 1876, while the controversy was still at its height, Pasteur +was prevailed upon to take the matter in hand. The great chemist was +becoming more and more exclusively a biologist as the years passed, and +in recent years his famous studies of the silk-worm diseases, which he +proved due to bacterial infection, and of the question of spontaneous +generation, had given him unequalled resources in microscopical +technique. And so when, with the aid of his laboratory associates +Duclaux and Chamberland and Roux, he took up the mooted anthrax question +the scientific world awaited the issue with bated breath. And when, in +1877, Pasteur was ready to report on his studies of anthrax, he came +forward with such a wealth of demonstrative experiments--experiments +the rigid accuracy of which no one would for a moment think of +questioning--going to prove the bacterial origin of anthrax, that +scepticism was at last quieted for all time to come. + +Henceforth no one could doubt that the contagious disease anthrax is due +exclusively to the introduction into an animal's system of a specific +germ--a microscopic plant--which develops there. And no logical mind +could have a reasonable doubt that what is proved true of one infectious +disease would some day be proved true also of other, perhaps of all, +forms of infectious maladies. + +Hitherto the cause of contagion, by which certain maladies spread from +individual to individual, had been a total mystery, quite unillumined +by the vague terms "miasm," "humor," "virus," and the like cloaks of +ignorance. Here and there a prophet of science, as Schwann and Henle, +had guessed the secret; but guessing, in science, is far enough from +knowing. Now, for the first time, the world KNEW, and medicine had taken +another gigantic stride towards the heights of exact science. + + +LISTER AND ANTISEPTIC SURGERY + +Meantime, in a different though allied field of medicine there had +been a complementary growth that led to immediate results of even more +practical importance. I mean the theory and practice of antisepsis in +surgery. This advance, like the other, came as a direct outgrowth of +Pasteur's fermentation studies of alcoholic beverages, though not at +the hands of Pasteur himself. Struck by the boundless implications of +Pasteur's revelations regarding the bacteria, Dr. Joseph Lister (the +present Lord Lister), then of Glasgow, set about as early as 1860 to +make a wonderful application of these ideas. If putrefaction is always +due to bacterial development, he argued, this must apply as well to +living as to dead tissues; hence the putrefactive changes which occur +in wounds and after operations on the human subject, from which +blood-poisoning so often follows, might be absolutely prevented if the +injured surfaces could be kept free from access of the germs of decay. + +In the hope of accomplishing this result, Lister began experimenting +with drugs that might kill the bacteria without injury to the patient, +and with means to prevent further access of germs once a wound was freed +from them. How well he succeeded all the world knows; how bitterly +he was antagonized for about a score of years, most of the world has +already forgotten. As early as 1867 Lister was able to publish results +pointing towards success in his great project; yet so incredulous were +surgeons in general that even some years later the leading surgeons +on the Continent had not so much as heard of his efforts. In 1870 the +soldiers of Paris died, as of old, of hospital gangrene; and when, +in 1871, the French surgeon Alphonse Guerin, stimulated by Pasteur's +studies, conceived the idea of dressing wounds with cotton in the hope +of keeping germs from entering them, he was quite unaware that a +British contemporary had preceded him by a full decade in this effort at +prevention and had made long strides towards complete success. Lister's +priority, however, and the superiority of his method, were freely +admitted by the French Academy of Sciences, which in 1881 officially +crowned his achievement, as the Royal Society of London had done the +year before. + +By this time, to be sure, as everybody knows, Lister's new methods had +made their way everywhere, revolutionizing the practice of surgery and +practically banishing from the earth maladies that hitherto had been the +terror of the surgeon and the opprobrium of his art. And these bedside +studies, conducted in the end by thousands of men who had no knowledge +of microscopy, had a large share in establishing the general belief in +the causal relation that micro-organisms bear to disease, which by about +the year 1880 had taken possession of the medical world. But they did +more; they brought into equal prominence the idea that, the cause of +a diseased condition being known, it maybe possible as never before to +grapple with and eradicate that condition. + + +PREVENTIVE INOCULATION + +The controversy over spontaneous generation, which, thanks to Pasteur +and Tyndall, had just been brought to a termination, made it clear that +no bacterium need be feared where an antecedent bacterium had not +found lodgment; Listerism in surgery had now shown how much might be +accomplished towards preventing the access of germs to abraded surfaces +of the body and destroying those that already had found lodgment there. +As yet, however, there was no inkling of a way in which a corresponding +onslaught might be made upon those other germs which find their way into +the animal organism by way of the mouth and the nostrils, and which, as +was now clear, are the cause of those contagious diseases which, first +and last, claim so large a proportion of mankind for their victims. +How such means might be found now became the anxious thought of every +imaginative physician, of every working microbiologist. + +As it happened, the world was not kept long in suspense. Almost before +the proposition had taken shape in the minds of the other leaders, +Pasteur had found a solution. Guided by the empirical success of Jenner, +he, like many others, had long practised inoculation experiments, and on +February 9, 1880, he announced to the French Academy of Sciences that he +had found a method of so reducing the virulence of a disease germ that +when introduced into the system of a susceptible animal it produced only +a mild form of the disease, which, however, sufficed to protect against +the usual virulent form exactly as vaccinia protects against small-pox. +The particular disease experimented with was that infectious malady of +poultry known familiarly as "chicken cholera." In October of the same +year Pasteur announced the method by which this "attenuation of the +virus," as he termed it, had been brought about--by cultivation of the +disease germs in artificial media, exposed to the air, and he did not +hesitate to assert his belief that the method would prove "susceptible +of generalization"--that is to say, of application to other diseases +than the particular one in question. + +Within a few months he made good this prophecy, for in February, +1881, he announced to the Academy that with the aid, as before, of his +associates MM. Chamberland and Roux, he had produced an attenuated virus +of the anthrax microbe by the use of which, as he affirmed with great +confidence, he could protect sheep, and presumably cattle, against that +fatal malady. "In some recent publications," said Pasteur, "I announced +the first case of the attenuation of a virus by experimental methods +only. Formed of a special microbe of an extreme minuteness, this virus +may be multiplied by artificial culture outside the animal body. These +cultures, left alone without any possible external contamination, +undergo, in the course of time, modifications of their virulency to a +greater or less extent. The oxygen of the atmosphere is said to be +the chief cause of these attenuations--that is, this lessening of the +facilities of multiplication of the microbe; for it is evident that the +difference of virulence is in some way associated with differences of +development in the parasitic economy. + +"There is no need to insist upon the interesting character of these +results and the deductions to be made therefrom. To seek to lessen the +virulence by rational means would be to establish, upon an experimental +basis, the hope of preparing from an active virus, easily cultivated +either in the human or animal body, a vaccine-virus of restrained +development capable of preventing the fatal effects of the former. +Therefore, we have applied all our energies to investigate the possible +generalizing action of atmospheric oxygen in the attenuation of virus. + +"The anthrax virus, being one that has been most carefully studied, +seemed to be the first that should attract our attention. Every time, +however, we encountered a difficulty. Between the microbe of chicken +cholera and the microbe of anthrax there exists an essential difference +which does not allow the new experiment to be verified by the old. +The microbes of chicken cholera do not, in effect, seem to resolve +themselves, in their culture, into veritable germs. The latter are +merely cells, or articulations always ready to multiply by division, +except when the particular conditions in which they become true germs +are known. + +"The yeast of beer is a striking example of these cellular productions, +being able to multiply themselves indefinitely without the apparition +of their original spores. There exist many mucedines (Mucedinae?) of +tubular mushrooms, which in certain conditions of culture produce +a chain of more or less spherical cells called Conidae. The latter, +detached from their branches, are able to reproduce themselves in the +form of cells, without the appearance, at least with a change in the +conditions of culture, of the spores of their respective mucedines. +These vegetable organisms can be compared to plants which are cultivated +by slipping, and to produce which it is not necessary to have the fruits +or the seeds of the mother plant. + +"The anthrax bacterium, in its artificial cultivation, behaves very +differently. Its mycelian filaments, if one may so describe them, have +been produced scarcely for twenty-four or forty-eight hours when they +are seen to transform themselves, those especially which are in free +contact with the air, into very refringent corpuscles, capable of +gradually isolating themselves into true germs of slight organization. +Moreover, observation shows that these germs, formed so quickly in the +culture, do not undergo, after exposure for a time to atmospheric air, +any change either in their vitality or their virulence. I was able to +present to the Academy a tube containing some spores of anthrax bacteria +produced four years ago, on March 21, 1887. Each year the germination +of these little corpuscles has been tried, and each year the germination +has been accomplished with the same facility and the same rapidity as at +first. Each year also the virulence of the new cultures has been tested, +and they have not shown any visible falling off. Therefore, how can we +experiment with the action of the air upon the anthrax virus with any +expectation of making it less virulent? + +"The crucial difficulty lies perhaps entirely in this rapid reproduction +of the bacteria germs which we have just related. In its form of a +filament, and in its multiplication by division, is not this organism at +all points comparable with the microbe of the chicken cholera? + +"That a germ, properly so called, that a seed, does not suffer any +modification on account of the air is easily conceived; but it is +conceivable not less easily that if there should be any change it would +occur by preference in the case of a mycelian fragment. It is thus that +a slip which may have been abandoned in the soil in contact with the air +does not take long to lose all vitality, while under similar conditions +a seed is preserved in readiness to reproduce the plant. If these views +have any foundation, we are led to think that in order to prove the +action of the air upon the anthrax bacteria it will be indispensable to +submit to this action the mycelian development of the minute organism +under conditions where there cannot be the least admixture of +corpuscular germs. Hence the problem of submitting the bacteria to the +action of oxygen comes back to the question of presenting entirely +the formation of spores. The question being put in this way, we are +beginning to recognize that it is capable of being solved. + +"We can, in fact, prevent the appearance of spores in the artificial +cultures of the anthrax parasite by various artifices. At the lowest +temperature at which this parasite can be cultivated--that is to say, +about +16 degrees Centigrade--the bacterium does not produce germs--at +any rate, for a very long time. The shapes of the minute microbe at this +lowest limit of its development are irregular, in the form of balls and +pears--in a word, they are monstrosities--but they are without spores. +In the last regard also it is the same at the highest temperatures at +which the parasite can be cultivated, temperatures which vary slightly +according to the means employed. In neutral chicken bouillon the +bacteria cannot be cultivated above 45 degrees. Culture, however, is +easy and abundant at 42 to 43 degrees, but equally without any formation +of spores. Consequently a culture of mycelian bacteria can be kept +entirely free from germs while in contact with the open air at a +temperature of from 42 to 43 degrees Centigrade. Now appear the three +remarkable results. After about one month of waiting the culture +dies--that is to say, if put into a fresh bouillon it becomes absolutely +sterile. + +"So much for the life and nutrition of this organism. In respect to its +virulence, it is an extraordinary fact that it disappears entirely after +eight days' culture at 42 to 43 degrees Centigrade, or, at any rate, the +cultures are innocuous for the guinea-pig, the rabbit, and the sheep, +the three kinds of animals most apt to contract anthrax. We are thus +able to obtain, not only the attenuation of the virulence, but also its +complete suppression by a simple method of cultivation. Moreover, we see +also the possibility of preserving and cultivating the terrible microbe +in an inoffensive state. What is it that happens in these eight days at +43 degrees that suffices to take away the virulence of the bacteria? Let +us remember that the microbe of chicken cholera dies in contact with the +air, in a period somewhat protracted, it is true, but after successive +attenuations. Are we justified in thinking that it ought to be the same +in regard to the microbe of anthrax? This hypothesis is confirmed +by experiment. Before the disappearance of its virulence the anthrax +microbe passes through various degrees of attenuation, and, moreover, +as is also the case with the microbe of chicken cholera, each of these +attenuated states of virulence can be obtained by cultivation. Moreover, +since, according to one of our recent Communications, anthrax is +not recurrent, each of our attenuated anthrax microbes is, for the +better-developed microbe, a vaccine--that is to say, a virus producing a +less-malignant malady. What, therefore, is easier than to find in these +a virus that will infect with anthrax sheep, cows, and horses, without +killing them, and ultimately capable of warding off the mortal malady? +We have practised this experiment with great success upon sheep, and +when the season comes for the assembling of the flocks at Beauce we +shall try the experiment on a larger scale. + +"Already M. Toussaint has announced that sheep can be saved by +preventive inoculations; but when this able observer shall have +published his results; on the subject of which we have made such +exhaustive studies, as yet unpublished, we shall be able to see the +whole difference which exists between the two methods--the uncertainty +of the one and the certainty of the other. That which we announce has, +moreover, the very great advantage of resting upon the existence of +a poison vaccine cultivable at will, and which can be increased +indefinitely in the space of a few hours without having recourse to +infected blood."(8) + + +This announcement was immediately challenged in a way that brought it +to the attention of the entire world. The president of an agricultural +society, realizing the enormous importance of the subject, proposed to +Pasteur that his alleged discovery should be submitted to a decisive +public test. He proposed to furnish a drove of fifty sheep half of which +were to be inoculated with the attenuated virus of Pasteur. Subsequently +all the sheep were to be inoculated with virulent virus, all being kept +together in one pen under precisely the same conditions. The "protected" +sheep were to remain healthy; the unprotected ones to die of anthrax; +so read the terms of the proposition. Pasteur accepted the challenge; +he even permitted a change in the programme by which two goats were +substituted for two of the sheep, and ten cattle added, stipulating, +however, that since his experiments had not yet been extended to cattle +these should not be regarded as falling rigidly within the terms of the +test. + +It was a test to try the soul of any man, for all the world looked on +askance, prepared to deride the maker of so preposterous a claim as soon +as his claim should be proved baseless. Not even the fame of Pasteur +could make the public at large, lay or scientific, believe in the +possibility of what he proposed to accomplish. There was time for all +the world to be informed of the procedure, for the first "preventive" +inoculation--or vaccination, as Pasteur termed it--was made on May 5th, +the second on May 17th, and another interval of two weeks must elapse +before the final inoculations with the unattenuated virus. Twenty-four +sheep, one goat, and five cattle were submitted to the preliminary +vaccinations. Then, on May 31 st, all sixty of the animals were +inoculated, a protected and unprotected one alternately, with an +extremely virulent culture of anthrax microbes that had been in +Pasteur's laboratory since 1877. This accomplished, the animals were +left together in one enclosure to await the issue. + +Two days later, June 2d, at the appointed hour of rendezvous, a vast +crowd, composed of veterinary surgeons, newspaper correspondents, and +farmers from far and near, gathered to witness the closing scenes of +this scientific tourney. What they saw was one of the most dramatic +scenes in the history of peaceful science--a scene which, as Pasteur +declared afterwards, "amazed the assembly." Scattered about the +enclosure, dead, dying, or manifestly sick unto death, lay the +unprotected animals, one and all, while each and every "protected" +animal stalked unconcernedly about with every appearance of perfect +health. Twenty of the sheep and the one goat were already dead; two +other sheep expired under the eyes of the spectators; the remaining +victims lingered but a few hours longer. Thus in a manner theatrical +enough, not to say tragic, was proclaimed the unequivocal victory of +science. Naturally enough, the unbelievers struck their colors and +surrendered without terms; the principle of protective vaccination, +with a virus experimentally prepared in the laboratory, was established +beyond the reach of controversy. + +That memorable scientific battle marked the beginning of a new era +in medicine. It was a foregone conclusion that the principle thus +established would be still further generalized; that it would be +applied to human maladies; that in all probability it would grapple +successfully, sooner or later, with many infectious diseases. That +expectation has advanced rapidly towards realization. Pasteur himself +made the application to the human subject in the disease hydrophobia in +1885, since which time that hitherto most fatal of maladies has largely +lost its terrors. Thousands of persons bitten by mad dogs have been +snatched from the fatal consequences of that mishap by this method at +the Pasteur Institute in Paris, and at the similar institutes, built on +the model of this parent one, that have been established all over the +world in regions as widely separated as New York and Nha-Trang. + + +SERUM-THERAPY + +In the production of the rabies vaccine Pasteur and his associates +developed a method of attenuation of a virus quite different from that +which had been employed in the case of the vaccines of chicken cholera +and of anthrax. The rabies virus was inoculated into the system of +guinea-pigs or rabbits and, in effect, cultivated in the systems of +these animals. The spinal cord of these infected animals was found to +be rich in the virus, which rapidly became attenuated when the cord was +dried in the air. The preventive virus, of varying strengths, was made +by maceration of these cords at varying stages of desiccation. This +cultivation of a virus within the animal organism suggested, no doubt, +by the familiar Jennerian method of securing small-pox vaccine, was at +the same time a step in the direction of a new therapeutic procedure +which was destined presently to become of all-absorbing importance--the +method, namely, of so-called serum-therapy, or the treatment of a +disease with the blood serum of an animal that has been subjected to +protective inoculation against that disease. + +The possibility of such a method was suggested by the familiar +observation, made by Pasteur and numerous other workers, that animals +of different species differ widely in their susceptibility to various +maladies, and that the virus of a given disease may become more and more +virulent when passed through the systems of successive individuals +of one species, and, contrariwise, less and less virulent when passed +through the systems of successive individuals of another species. These +facts suggested the theory that the blood of resistant animals might +contain something directly antagonistic to the virus, and the hope that +this something might be transferred with curative effect to the blood +of an infected susceptible animal. Numerous experimenters all over the +world made investigations along the line of this alluring possibility, +the leaders perhaps being Drs. Behring and Kitasato, closely followed by +Dr. Roux and his associates of the Pasteur Institute of Paris. Definite +results were announced by Behring in 1892 regarding two important +diseases--tetanus and diphtheria--but the method did not come into +general notice until 1894, when Dr. Roux read an epoch-making paper on +the subject at the Congress of Hygiene at Buda-Pesth. + +In this paper Dr. Roux, after adverting to the labors of Behring, +Ehrlich, Boer, Kossel, and Wasserman, described in detail the methods +that had been developed at the Pasteur Institute for the development of +the curative serum, to which Behring had given the since-familiar name +antitoxine. The method consists, first, of the cultivation, for some +months, of the diphtheria bacillus (called the Klebs-Loeffler bacillus, +in honor of its discoverers) in an artificial bouillon, for the +development of a powerful toxine capable of giving the disease in a +virulent form. + +This toxine, after certain details of mechanical treatment, is injected +in small but increasing doses into the system of an animal, care being +taken to graduate the amount so that the animal does not succumb to the +disease. After a certain course of this treatment it is found that a +portion of blood serum of the animal so treated will act in a curative +way if injected into the blood of another animal, or a human patient, +suffering with diphtheria. In other words, according to theory, an +antitoxine has been developed in the system of the animal subjected to +the progressive inoculations of the diphtheria toxine. In Dr. Roux's +experience the animal best suited for the purpose is the horse, though +almost any of the domesticated animals will serve the purpose. + +But Dr. Roux's paper did not stop with the description of laboratory +methods. It told also of the practical application of the serum to +the treatment of numerous cases of diphtheria in the hospitals of +Paris--applications that had met with a gratifying measure of success. +He made it clear that a means had been found of coping successfully with +what had been one of the most virulent and intractable of the diseases +of childhood. Hence it was not strange that his paper made a sensation +in all circles, medical and lay alike. + +Physicians from all over the world flocked to Paris to learn the details +of the open secret, and within a few months the new serum-therapy had +an acknowledged standing with the medical profession everywhere. What it +had accomplished was regarded as but an earnest of what the new +method might accomplish presently when applied to the other infectious +diseases. + +Efforts at such applications were immediately begun in numberless +directions--had, indeed, been under way in many a laboratory for some +years before. It is too early yet to speak of the results in detail. But +enough has been done to show that this method also is susceptible of the +widest generalization. It is not easy at the present stage to sift that +which is tentative from that which will be permanent; but so great an +authority as Behring does not hesitate to affirm that today we possess, +in addition to the diphtheria antitoxine, equally specific antitoxines +of tetanus, cholera, typhus fever, pneumonia, and tuberculosis--a set +of diseases which in the aggregate account for a startling proportion +of the general death-rate. Then it is known that Dr. Yersin, with the +collaboration of his former colleagues of the Pasteur Institute, has +developed, and has used with success, an antitoxine from the microbe of +the plague which recently ravaged China. + +Dr. Calmette, another graduate of the Pasteur Institute, has extended +the range of the serum-therapy to include the prevention and treatment +of poisoning by venoms, and has developed an antitoxine that has already +given immunity from the lethal effects of snake bites to thousands of +persons in India and Australia. + +Just how much of present promise is tentative, just what are the limits +of the methods--these are questions for the future to decide. But, in +any event, there seems little question that the serum treatment will +stand as the culminating achievement in therapeutics of our century. +It is the logical outgrowth of those experimental studies with the +microscope begun by our predecessors of the thirties, and it represents +the present culmination of the rigidly experimental method which has +brought medicine from a level of fanciful empiricism to the plane of a +rational experimental science. + + + + +IX. THE NEW SCIENCE OF EXPERIMENTAL PSYCHOLOGY + +BRAIN AND MIND + +A little over a hundred years ago a reform movement was afoot in the +world in the interests of the insane. As was fitting, the movement +showed itself first in America, where these unfortunates were humanely +cared for at a time when their treatment elsewhere was worse than +brutal; but England and France quickly fell into line. The leader on +this side of the water was the famous Philadelphian, Dr. Benjamin Rush, +"the Sydenham of America"; in England, Dr. William Tuke inaugurated the +movement; and in France, Dr. Philippe Pinel, single-handed, led the way. +Moved by a common spirit, though acting quite independently, these +men raised a revolt against the traditional custom which, spurning the +insane as demon-haunted outcasts, had condemned these unfortunates to +dungeons, chains, and the lash. Hitherto few people had thought it other +than the natural course of events that the "maniac" should be thrust +into a dungeon, and perhaps chained to the wall with the aid of an iron +band riveted permanently about his neck or waist. Many an unfortunate, +thus manacled, was held to the narrow limits of his chain for +years together in a cell to which full daylight never penetrated; +sometimes--iron being expensive--the chain was so short that the +wretched victim could not rise to the upright posture or even shift his +position upon his squalid pallet of straw. + +In America, indeed, there being no Middle Age precedents to crystallize +into established customs, the treatment accorded the insane had seldom +or never sunk to this level. Partly for this reason, perhaps, the work +of Dr. Rush at the Philadelphia Hospital, in 1784, by means of which the +insane came to be humanely treated, even to the extent of banishing the +lash, has been but little noted, while the work of the European leaders, +though belonging to later decades, has been made famous. And perhaps +this is not as unjust as it seems, for the step which Rush took, from +relatively bad to good, was a far easier one to take than the leap from +atrocities to good treatment which the European reformers were obliged +to compass. In Paris, for example, Pinel was obliged to ask permission +of the authorities even to make the attempt at liberating the insane +from their chains, and, notwithstanding his recognized position as a +leader of science, he gained but grudging assent, and was regarded as +being himself little better than a lunatic for making so manifestly +unwise and hopeless an attempt. Once the attempt had been made, however, +and carried to a successful issue, the amelioration wrought in the +condition of the insane was so patent that the fame of Pinel's work at +the Bicetre and the Salpetriere went abroad apace. It required, indeed, +many years to complete it in Paris, and a lifetime of effort on the +part of Pinel's pupil Esquirol and others to extend the reform to the +provinces; but the epochal turning-point had been reached with Pinel's +labors of the closing years of the eighteenth century. + +The significance of this wise and humane reform, in the present +connection, is the fact that these studies of the insane gave emphasis +to the novel idea, which by-and-by became accepted as beyond question, +that "demoniacal possession" is in reality no more than the outward +expression of a diseased condition of the brain. This realization made +it clear, as never before, how intimately the mind and the body are +linked one to the other. And so it chanced that, in striking the +shackles from the insane, Pinel and his confreres struck a blow also, +unwittingly, at time-honored philosophical traditions. The liberation +of the insane from their dungeons was an augury of the liberation of +psychology from the musty recesses of metaphysics. Hitherto psychology, +in so far as it existed at all, was but the subjective study of +individual minds; in future it must become objective as well, taking +into account also the relations which the mind bears to the body, and in +particular to the brain and nervous system. + +The necessity for this collocation was advocated quite as earnestly, and +even more directly, by another worker of this period, whose studies were +allied to those of alienists, and who, even more actively than they, +focalized his attention upon the brain and its functions. This earliest +of specialists in brain studies was a German by birth but Parisian +by adoption, Dr. Franz Joseph Gall, originator of the since-notorious +system of phrenology. The merited disrepute into which this system has +fallen through the exposition of peripatetic charlatans should not +make us forget that Dr. Gall himself was apparently a highly educated +physician, a careful student of the brain and mind according to the best +light of his time, and, withal, an earnest and honest believer in the +validity of the system he had originated. The system itself, taken as a +whole, was hopelessly faulty, yet it was not without its latent germ +of truth, as later studies were to show. How firmly its author himself +believed in it is evidenced by the paper which he contributed to the +French Academy of Sciences in 1808. The paper itself was referred to a +committee of which Pinel and Cuvier were members. The verdict of this +committee was adverse, and justly so; yet the system condemned had at +least one merit which its detractors failed to realize. It popularized +the conception that the brain is the organ of mind. Moreover, by its +insistence it rallied about it a band of scientific supporters, chief of +whom was Dr. Kaspar Spurzlieim, a man of no mean abilities, who became +the propagandist of phrenology in England and in America. Of course such +advocacy and popularity stimulated opposition as well, and out of the +disputations thus arising there grew presently a general interest in the +brain as the organ of mind, quite aside from any preconceptions whatever +as to the doctrines of Gall and Spurzheim. + +Prominent among the unprejudiced class of workers who now appeared was +the brilliant young Frenchman Louis Antoine Desmoulins, who studied +first under the tutorage of the famous Magendie, and published jointly +with him a classical work on the nervous system of vertebrates in +1825. Desmoulins made at least one discovery of epochal importance. He +observed that the brains of persons dying in old age were lighter than +the average and gave visible evidence of atrophy, and he reasoned that +such decay is a normal accompaniment of senility. No one nowadays would +question the accuracy of this observation, but the scientific world +was not quite ready for it in 1825; for when Desmoulins announced his +discovery to the French Academy, that august and somewhat patriarchal +body was moved to quite unscientific wrath, and forbade the young +iconoclast the privilege of further hearings. From which it is evident +that the partially liberated spirit of the new psychology had by no +means freed itself altogether, at the close of the first quarter of +the nineteenth century, from the metaphysical cobwebs of its long +incarceration. + + +FUNCTIONS OF THE NERVES + +While studies of the brain were thus being inaugurated, the nervous +system, which is the channel of communication between the brain and the +outside world, was being interrogated with even more tangible results. +The inaugural discovery was made in 1811 by Dr. (afterwards Sir Charles) +Bell,(1) the famous English surgeon and experimental physiologist. +It consisted of the observation that the anterior roots of the spinal +nerves are given over to the function of conveying motor impulses from +the brain outward, whereas the posterior roots convey solely sensory +impulses to the brain from without. Hitherto it had been supposed that +all nerves have a similar function, and the peculiar distribution of the +spinal nerves had been an unsolved puzzle. + +Bell's discovery was epochal; but its full significance was not +appreciated for a decade, nor, indeed, was its validity at first +admitted. In Paris, in particular, then the court of final appeal in +all matters scientific, the alleged discovery was looked at askance, or +quite ignored. But in 1823 the subject was taken up by the recognized +leader of French physiology--Francois Magendie--in the course of his +comprehensive experimental studies of the nervous system, and Bell's +conclusions were subjected to the most rigid experimental tests +and found altogether valid. Bell himself, meanwhile, had turned his +attention to the cranial nerves, and had proved that these also are +divisible into two sets--sensory and motor. Sometimes, indeed, the two +sets of filaments are combined into one nerve cord, but if traced to +their origin these are found to arise from different brain centres. Thus +it was clear that a hitherto unrecognized duality of function pertains +to the entire extra-cranial nervous system. Any impulse sent from the +periphery to the brain must be conveyed along a perfectly definite +channel; the response from the brain, sent out to the peripheral +muscles, must traverse an equally definite and altogether different +course. If either channel is interrupted--as by the section of its +particular nerve tract--the corresponding message is denied transmission +as effectually as an electric current is stopped by the section of the +transmitting wire. + +Experimenters everywhere soon confirmed the observations of Bell and +Magendie, and, as always happens after a great discovery, a fresh +impulse was given to investigations in allied fields. Nevertheless, a +full decade elapsed before another discovery of comparable importance +was made. Then Marshall Hall, the most famous of English physicians +of his day, made his classical observations on the phenomena +that henceforth were to be known as reflex action. In 1832, while +experimenting one day with a decapitated newt, he observed that the +headless creature's limbs would contract in direct response to certain +stimuli. Such a response could no longer be secured if the spinal +nerves supplying a part were severed. Hence it was clear that responsive +centres exist in the spinal cord capable of receiving a sensory message +and of transmitting a motor impulse in reply--a function hitherto +supposed to be reserved for the brain. Further studies went to show that +such phenomena of reflex action on the part of centres lying outside the +range of consciousness, both in the spinal cord and in the brain itself, +are extremely common; that, in short, they enter constantly into the +activities of every living organism and have a most important share in +the sum total of vital movements. Hence, Hall's discovery must always +stand as one of the great mile-stones of the advance of neurological +science. + +Hall gave an admirably clear and interesting account of his experiments +and conclusions in a paper before the Royal Society, "On the Reflex +Functions of the Medulla Oblongata and the Medulla Spinalis," from +which, as published in the Transactions of the society for 1833, we may +quote at some length: + +"In the entire animal, sensation and voluntary motion, functions of +the cerebrum, combine with the functions of the medulla oblongata and +medulla spinalis, and may therefore render it difficult or impossible to +determine those which are peculiar to each; if, in an animal deprived +of the brain, the spinal marrow or the nerves supplying the muscles be +stimulated, those muscles, whether voluntary or respiratory, are equally +thrown into contraction, and, it may be added, equally in the complete +and in the mutilated animal; and, in the case of the nerves, equally in +limbs connected with and detached from the spinal marrow. + +"The operation of all these various causes may be designated centric, as +taking place AT, or at least in a direction FROM, central parts of the +nervous system. But there is another function the phenomena of which +are of a totally different order and obey totally different laws, being +excited by causes in a situation which is EXCENTRIC in the nervous +system--that is, distant from the nervous centres. This mode of action +has not, I think, been hitherto distinctly understood by physiologists. + +"Many of the phenomena of this principle of action, as they occur in +the limbs, have certainly been observed. But, in the first place, this +function is by no means confined to the limbs; for, while it imparts +to each muscle its appropriate tone, and to each system of muscles its +appropriate equilibrium or balance, it performs the still more important +office of presiding over the orifices and terminations of each of the +internal canals in the animal economy, giving them their due form +and action; and, in the second place, in the instances in which the +phenomena of this function have been noticed, they have been confounded, +as I have stated, with those of sensation and volition; or, if they +have been distinguished from these, they have been too indefinitely +denominated instinctive, or automatic. I have been compelled, therefore, +to adopt some new designation for them, and I shall now give the reasons +for my choice of that which is given in the title of this paper--'Reflex +Functions.' + +"This property is characterized by being EXCITED in its action and +REFLEX in its course: in every instance in which it is exerted an +impression made upon the extremities of certain nerves is conveyed to +the medulla oblongata or the medulla spinalis, and is reflected along +the nerves to parts adjacent to, or remote from, that which has received +the impression. + +"It is by this reflex character that the function to which I have +alluded is to be distinguished from every other. There are, in the +animal economy, four modes of muscular action, of muscular contraction. +The first is that designated VOLUNTARY: volition, originated in the +cerebrum and spontaneous in its acts, extends its influence along the +spinal marrow and the motor nerves in a DIRECT LINE to the voluntary +muscles. The SECOND is that of RESPIRATION: like volition, the motive +influence in respiration passes in a DIRECT LINE from one point of the +nervous system to certain muscles; but as voluntary motion seems to +originate in the cerebrum, so the respiratory motions originate in +the medulla oblongata: like the voluntary motions, the motions of +respirations are spontaneous; they continue, at least, after the eighth +pair of nerves have been divided. The THIRD kind of muscular action +in the animal economy is that termed involuntary: it depends upon the +principle of irritability and requires the IMMEDIATE application of +a stimulus to the nervo-muscular fibre itself. These three kinds of +muscular motion are well known to physiologists; and I believe they are +all which have been hitherto pointed out. There is, however, a FOURTH, +which subsists, in part, after the voluntary and respiratory motions +have ceased, by the removal of the cerebrum and medulla oblongata, and +which is attached to the medulla spinalis, ceasing itself when this +is removed, and leaving the irritability undiminished. In this kind of +muscular motion the motive influence does not originate in any central +part of the nervous system, but from a distance from that centre; it is +neither spontaneous in its action nor direct in its course; it is, on +the contrary, EXCITED by the application of appropriate stimuli, which +are not, however, applied immediately to the muscular or nervo-muscular +fibre, but to certain membraneous parts, whence the impression is +carried through the medulla, REFLECTED and reconducted to the part +impressed, or conducted to a part remote from it in which muscular +contraction is effected. + +"The first three modes of muscular action are known only by actual +movements of muscular contractions. But the reflex function exists as +a continuous muscular action, as a power presiding over organs not +actually in a state of motion, preserving in some, as the glottis, an +open, in others, as the sphincters, a closed form, and in the limbs a +due degree of equilibrium or balanced muscular action--a function not, I +think, hitherto recognized by physiologists. + +"The three kinds of muscular motion hitherto known may be distinguished +in another way. The muscles of voluntary motion and of respiration may +be excited by stimulating the nerves which supply them, in any part of +their course, whether at their source as a part of the medulla oblongata +or the medulla spinalis or exterior to the spinal canal: the muscles of +involuntary motion are chiefly excited by the actual contact of stimuli. +In the case of the reflex function alone the muscles are excited by a +stimulus acting mediately and indirectly in a curved and reflex course, +along superficial subcutaneous or submucous nerves proceeding from the +medulla. The first three of these causes of muscular motion may act on +detached limbs or muscles. The last requires the connection with the +medulla to be preserved entire. + +"All the kinds of muscular motion may be unduly excited, but the reflex +function is peculiar in being excitable in two modes of action, not +previously subsisting in the animal economy, as in the case of sneezing, +coughing, vomiting, etc. The reflex function also admits of being +permanently diminished or augmented and of taking on some other morbid +forms, of which I shall treat hereafter. + +"Before I proceed to the details of the experiments upon which this +disposition rests, it may be well to point out several instances in +illustration of the various sources of and the modes of muscular action +which have been enumerated. None can be more familiar than the act of +swallowing. Yet how complicated is the act! The apprehension of the food +by the teeth and tongue, etc., is voluntary, and cannot, therefore, take +place in an animal from which the cerebrum is removed. The transition of +food over the glottis and along the middle and lower part of the pharynx +depends upon the reflex action: it can take place in animals from which +the cerebrum has been removed or the ninth pair of nerves divided; but +it requires the connection with the medulla oblongata to be preserved +entirely; and the actual contact of some substance which may act as a +stimulus: it is attended by the accurate closure of the glottis and by +the contraction of the pharynx. The completion of the act of deglutition +is dependent upon the stimulus immediately impressed upon the muscular +fibre of the oesophagus, and is the result of excited irritability. + +"However plain these observations may have made the fact that there is +a function of the nervous muscular system distinct from sensation, from +the voluntary and respiratory motions, and from irritability, it is +right, in every such inquiry as the present, that the statements and +reasonings should be made with the experiment, as it were, actually +before us. It has already been remarked that the voluntary and +respiratory motions are spontaneous, not necessarily requiring the +agency of a stimulus. If, then, an animal can be placed in such +circumstances that such motions will certainly not take place, the power +of moving remaining, it may be concluded that volition and the motive +influence of respiration are annihilated. Now this is effected by +removing the cerebrum and the medulla oblongata. These facts are fully +proved by the experiments of Legallois and M. Flourens, and by several +which I proceed to detail, for the sake of the opportunity afforded by +doing so of stating the arguments most clearly. + +"I divided the spinal marrow of a very lively snake between the second +and third vertebrae. The movements of the animal were immediately before +extremely vigorous and unintermitted. From the moment of the division +of the spinal marrow it lay perfectly tranquil and motionless, with the +exception of occasional gaspings and slight movements of the head. +It became quite evident that this state of quiescence would continue +indefinitely were the animal secured from all external impressions. + +"Being now stimulated, the body began to move with great activity, and +continued to do so for a considerable time, each change of position or +situation bringing some fresh part of the surface of the animal into +contact with the table or other objects and renewing the application of +stimulants. + +"At length the animal became again quiescent; and being carefully +protected from all external impressions it moved no more, but died in +the precise position and form which it had last assumed. + +"It requires a little manoeuvre to perform this experiment successfully: +the motions of the animal must be watched and slowly and cautiously +arrested by opposing some soft substance, as a glove or cotton wool; +they are by this means gradually lulled into quiescence. The slightest +touch with a hard substance, the slightest stimulus, will, on the other +hand, renew the movements on the animal in an active form. But that this +phenomenon does not depend upon sensation is further fully proved by the +facts that the position last assumed, and the stimuli, may be such as +would be attended by extreme or continued pain, if the sensibility were +undestroyed: in one case the animal remained partially suspended over +the acute edge of the table; in others the infliction of punctures and +the application of a lighted taper did not prevent the animal, still +possessed of active powers of motion, from passing into a state of +complete and permanent quiescence." + + +In summing up this long paper Hall concludes with this sentence: "The +reflex function appears in a word to be the COMPLEMENT of the functions +of the nervous system hitherto known."(2) + +All these considerations as to nerve currents and nerve tracts becoming +stock knowledge of science, it was natural that interest should +become stimulated as to the exact character of these nerve tracts in +themselves, and all the more natural in that the perfected microscope +was just now claiming all fields for its own. A troop of observers soon +entered upon the study of the nerves, and the leader here, as in so +many other lines of microscopical research, was no other than Theodor +Schwann. Through his efforts, and with the invaluable aid of such other +workers as Remak, Purkinje, Henle, Muller, and the rest, all the mystery +as to the general characteristics of nerve tracts was cleared away. It +came to be known that in its essentials a nerve tract is a tenuous fibre +or thread of protoplasm stretching between two terminal points in the +organism, one of such termini being usually a cell of the brain +or spinal cord, the other a distribution-point at or near the +periphery--for example, in a muscle or in the skin. Such a fibril may +have about it a protective covering, which is known as the sheath of +Schwann; but the fibril itself is the essential nerve tract; and in +many cases, as Remak presently discovered, the sheath is dispensed with, +particularly in case of the nerves of the so-called sympathetic system. + +This sympathetic system of ganglia and nerves, by-the-bye, had long been +a puzzle to the physiologists. Its ganglia, the seeming centre of +the system, usually minute in size and never very large, are found +everywhere through the organism, but in particular are gathered into a +long double chain which lies within the body cavity, outside the spinal +column, and represents the sole nervous system of the non-vertebrated +organisms. Fibrils from these ganglia were seen to join the cranial and +spinal nerve fibrils and to accompany them everywhere, but what special +function they subserved was long a mere matter of conjecture and led to +many absurd speculations. Fact was not substituted for conjecture +until about the year 1851, when the great Frenchman Claude Bernard +conclusively proved that at least one chief function of the sympathetic +fibrils is to cause contraction of the walls of the arterioles of the +system, thus regulating the blood-supply of any given part. Ten years +earlier Henle had demonstrated the existence of annular bands of muscle +fibres in the arterioles, hitherto a much-mooted question, and several +tentative explanations of the action of these fibres had been made, +particularly by the brothers Weber, by Stilling, who, as early as 1840, +had ventured to speak of "vaso-motor" nerves, and by Schiff, who was +hard upon the same track at the time of Bernard's discovery. But a clear +light was not thrown on the subject until Bernard's experiments were +made in 1851. The experiments were soon after confirmed and extended +by Brown-Sequard, Waller, Budge, and numerous others, and henceforth +physiologists felt that they understood how the blood-supply of any +given part is regulated by the nervous system. + +In reality, however, they had learned only half the story, as Bernard +himself proved only a few years later by opening up a new and quite +unsuspected chapter. While experimenting in 1858 he discovered that +there are certain nerves supplying the heart which, if stimulated, +cause that organ to relax and cease beating. As the heart is essentially +nothing more than an aggregation of muscles, this phenomenon was utterly +puzzling and without precedent in the experience of physiologists. An +impulse travelling along a motor nerve had been supposed to be able to +cause a muscular contraction and to do nothing else; yet here such an +impulse had exactly the opposite effect. The only tenable explanation +seemed to be that this particular impulse must arrest or inhibit the +action of the impulses that ordinarily cause the heart muscles to +contract. But the idea of such inhibition of one impulse by another was +utterly novel and at first difficult to comprehend. Gradually, however, +the idea took its place in the current knowledge of nerve physiology, +and in time it came to be understood that what happens in the case of +the heart nerve-supply is only a particular case under a very general, +indeed universal, form of nervous action. Growing out of Bernard's +initial discovery came the final understanding that the entire nervous +system is a mechanism of centres subordinate and centres superior, the +action of the one of which may be counteracted and annulled in effect +by the action of the other. This applies not merely to such physical +processes as heart-beats and arterial contraction and relaxing, but +to the most intricate functionings which have their counterpart in +psychical processes as well. Thus the observation of the inhibition of +the heart's action by a nervous impulse furnished the point of departure +for studies that led to a better understanding of the modus operandi of +the mind's activities than had ever previously been attained by the most +subtle of psychologists. + + +PSYCHO-PHYSICS + +The work of the nerve physiologists had thus an important bearing on +questions of the mind. But there was another company of workers of +this period who made an even more direct assault upon the "citadel of +thought." A remarkable school of workers had been developed in Germany, +the leaders being men who, having more or less of innate metaphysical +bias as a national birthright, had also the instincts of the empirical +scientist, and whose educational equipment included a profound knowledge +not alone of physiology and psychology, but of physics and mathematics +as well. These men undertook the novel task of interrogating the +relations of body and mind from the standpoint of physics. They sought +to apply the vernier and the balance, as far as might be, to the +intangible processes of mind. + +The movement had its precursory stages in the early part of the century, +notably in the mathematical psychology of Herbart, but its first +definite output to attract general attention came from the master-hand +of Hermann Helmholtz in 1851. It consisted of the accurate measurement +of the speed of transit of a nervous impulse along a nerve tract. To +make such measurement had been regarded as impossible, it being supposed +that the flight of the nervous impulse was practically instantaneous. +But Helmholtz readily demonstrated the contrary, showing that the +nerve cord is a relatively sluggish message-bearer. According to his +experiments, first performed upon the frog, the nervous "current" +travels less than one hundred feet per second. Other experiments +performed soon afterwards by Helmholtz himself, and by various +followers, chief among whom was Du Bois-Reymond, modified somewhat the +exact figures at first obtained, but did not change the general bearings +of the early results. Thus the nervous impulse was shown to be something +far different, as regards speed of transit, at any rate, from the +electric current to which it had been so often likened. An electric +current would flash halfway round the globe while a nervous impulse +could travel the length of the human body--from a man's foot to his +brain. + +The tendency to bridge the gulf that hitherto had separated the physical +from the psychical world was further evidenced in the following decade +by Helmholtz's remarkable but highly technical study of the sensations +of sound and of color in connection with their physical causes, in the +course of which he revived the doctrine of color vision which that other +great physiologist and physicist, Thomas Young, had advanced half +a century before. The same tendency was further evidenced by the +appearance, in 1852, of Dr. Hermann Lotze's famous Medizinische +Psychologie, oder Physiologie der Seele, with its challenge of the old +myth of a "vital force." But the most definite expression of the new +movement was signalized in 1860, when Gustav Fechner published his +classical work called Psychophysik. That title introduced a new word +into the vocabulary of science. Fechner explained it by saying, "I mean +by psychophysics an exact theory of the relation between spirit and +body, and, in a general way, between the physical and the psychic +worlds." The title became famous and the brunt of many a controversy. +So also did another phrase which Fechner introduced in the course of +his book--the phrase "physiological psychology." In making that happy +collocation of words Fechner virtually christened a new science. + + +FECHNER EXPOUNDS WEBER'S LAW + +The chief purport of this classical book of the German +psycho-physiologist was the elaboration and explication of experiments +based on a method introduced more than twenty years earlier by his +countryman E. H. Weber, but which hitherto had failed to attract the +attention it deserved. The method consisted of the measurement and +analysis of the definite relation existing between external stimuli +of varying degrees of intensity (various sounds, for example) and the +mental states they induce. Weber's experiments grew out of the familiar +observation that the nicety of our discriminations of various sounds, +weights, or visual images depends upon the magnitude of each particular +cause of a sensation in its relation with other similar causes. Thus, +for example, we cannot see the stars in the daytime, though they shine +as brightly then as at night. Again, we seldom notice the ticking of a +clock in the daytime, though it may become almost painfully audible in +the silence of the night. Yet again, the difference between an ounce +weight and a two-ounce weight is clearly enough appreciable when we +lift the two, but one cannot discriminate in the same way between a +five-pound weight and a weight of one ounce over five pounds. + +This last example, and similar ones for the other senses, gave Weber +the clew to his novel experiments. Reflection upon every-day experiences +made it clear to him that whenever we consider two visual sensations, or +two auditory sensations, or two sensations of weight, in comparison +one with another, there is always a limit to the keenness of our +discrimination, and that this degree of keenness varies, as in the case +of the weights just cited, with the magnitude of the exciting cause. + +Weber determined to see whether these common experiences could be +brought within the pale of a general law. His method consisted of making +long series of experiments aimed at the determination, in each case, of +what came to be spoken of as the least observable difference between the +stimuli. Thus if one holds an ounce weight in each hand, and has tiny +weights added to one of them, grain by grain, one does not at first +perceive a difference; but presently, on the addition of a certain +grain, he does become aware of the difference. Noting now how many +grains have been added to produce this effect, we have the weight which +represents the least appreciable difference when the standard is one +ounce. + +Now repeat the experiment, but let the weights be each of five pounds. +Clearly in this case we shall be obliged to add not grains, but drachms, +before a difference between the two heavy weights is perceived. But +whatever the exact amount added, that amount represents the stimulus +producing a just-perceivable sensation of difference when the standard +is five pounds. And so on for indefinite series of weights of varying +magnitudes. Now came Weber's curious discovery. Not only did he find +that in repeated experiments with the same pair of weights the measure +of "just-{p}erceivable difference" remained approximately fixed, but +he found, further, that a remarkable fixed relation exists between +the stimuli of different magnitude. If, for example, he had found it +necessary, in the case of the ounce weights, to add one-fiftieth of an +ounce to the one before a difference was detected, he found also, in the +case of the five-pound weights, that one-fiftieth of five pounds must be +added before producing the same result. And so of all other weights; the +amount added to produce the stimulus of "least-appreciable difference" +always bore the same mathematical relation to the magnitude of the +weight used, be that magnitude great or small. + +Weber found that the same thing holds good for the stimuli of the +sensations of sight and of hearing, the differential stimulus bearing +always a fixed ratio to the total magnitude of the stimuli. Here, then, +was the law he had sought. + +Weber's results were definite enough and striking enough, yet they +failed to attract any considerable measure of attention until they were +revived and extended by Fechner and brought before the world in the +famous work on psycho-physics. Then they precipitated a veritable +melee. Fechner had not alone verified the earlier results (with certain +limitations not essential to the present consideration), but had +invented new methods of making similar tests, and had reduced the whole +question to mathematical treatment. He pronounced Weber's discovery +the fundamental law of psycho-physics. In honor of the discoverer, +he christened it Weber's Law. He clothed the law in words and in +mathematical formulae, and, so to say, launched it full tilt at the +heads of the psychological world. It made a fine commotion, be assured, +for it was the first widely heralded bulletin of the new psychology +in its march upon the strongholds of the time-honored metaphysics. The +accomplishments of the microscopists and the nerve physiologists had +been but preliminary--mere border skirmishes of uncertain import. But +here was proof that the iconoclastic movement meant to invade the very +heart of the sacred territory of mind--a territory from which tangible +objective fact had been supposed to be forever barred. + + +PHYSIOLOGICAL PSYCHOLOGY + +Hardly had the alarm been sounded, however, before a new movement was +made. While Fechner's book was fresh from the press, steps were being +taken to extend the methods of the physicist in yet another way to +the intimate processes of the mind. As Helmholtz had shown the rate of +nervous impulsion along the nerve tract to be measurable, it was +now sought to measure also the time required for the central nervous +mechanism to perform its work of receiving a message and sending out +a response. This was coming down to the very threshold of mind. The +attempt was first made by Professor Donders in 1861, but definitive +results were only obtained after many years of experiment on the part +of a host of observers. The chief of these, and the man who has stood +in the forefront of the new movement and has been its recognized leader +throughout the remainder of the century, is Dr. Wilhelm Wundt, of +Leipzig. + +The task was not easy, but, in the long run, it was accomplished. Not +alone was it shown that the nerve centre requires a measurable time for +its operations, but much was learned as to conditions that modify this +time. Thus it was found that different persons vary in the rate of their +central nervous activity--which explained the "personal equation" that +the astronomer Bessel had noted a half-century before. It was found, +too, that the rate of activity varies also for the same person under +different conditions, becoming retarded, for example, under influence of +fatigue, or in case of certain diseases of the brain. All details aside, +the essential fact emerges, as an experimental demonstration, that the +intellectual processes--sensation, apperception, volition--are linked +irrevocably with the activities of the central nervous tissues, and +that these activities, like all other physical processes, have a time +element. To that old school of psychologists, who scarcely cared more +for the human head than for the heels--being interested only in the +mind--such a linking of mind and body as was thus demonstrated was +naturally disquieting. But whatever the inferences, there was no +escaping the facts. + +Of course this new movement has not been confined to Germany. Indeed, +it had long had exponents elsewhere. Thus in England, a full century +earlier, Dr. Hartley had championed the theory of the close and +indissoluble dependence of the mind upon the brain, and formulated +a famous vibration theory of association that still merits careful +consideration. Then, too, in France, at the beginning of the century, +there was Dr. Cabanis with his tangible, if crudely phrased, doctrine +that the brain digests impressions and secretes thought as the stomach +digests food and the liver secretes bile. Moreover, Herbert Spencer's +Principles of Psychology, with its avowed co-ordination of mind and body +and its vitalizing theory of evolution, appeared in 1855, half a +decade before the work of Fechner. But these influences, though of vast +educational value, were theoretical rather than demonstrative, and the +fact remains that the experimental work which first attempted to gauge +mental operations by physical principles was mainly done in Germany. +Wundt's Physiological Psychology, with its full preliminary descriptions +of the anatomy of the nervous system, gave tangible expression to the +growth of the new movement in 1874; and four years later, with the +opening of his laboratory of physiological psychology at the University +of Leipzig, the new psychology may be said to have gained a permanent +foothold and to have forced itself into official recognition. From then +on its conquest of the world was but a matter of time. + +It should be noted, however, that there is one other method of strictly +experimental examination of the mental field, latterly much in vogue, +which had a different origin. This is the scientific investigation of +the phenomena of hypnotism. This subject was rescued from the hands of +charlatans, rechristened, and subjected to accurate investigation by +Dr. James Braid, of Manchester, as early as 1841. But his results, after +attracting momentary attention, fell from view, and, despite desultory +efforts, the subject was not again accorded a general hearing from +the scientific world until 1878, when Dr. Charcot took it up at +the Salpetriere, in Paris, followed soon afterwards by Dr. Rudolf +Heidenhain, of Breslau, and a host of other experimenters. The value +of the method in the study of mental states was soon apparent. Most +of Braid's experiments were repeated, and in the main his results were +confirmed. His explanation of hypnotism, or artificial somnambulism, +as a self-induced state, independent of any occult or supersensible +influence, soon gained general credence. His belief that the initial +stages are due to fatigue of nervous centres, usually from excessive +stimulation, has not been supplanted, though supplemented by notions +growing out of the new knowledge as to subconscious mentality in +general, and the inhibitory influence of one centre over another in the +central nervous mechanism. + + +THE BRAIN AS THE ORGAN OF MIND + +These studies of the psychologists and pathologists bring the relations +of mind and body into sharp relief. But even more definite in this +regard was the work of the brain physiologists. Chief of these, during +the middle period of the century, was the man who is sometimes spoken of +as the "father of brain physiology," Marie Jean Pierre Flourens, of the +Jardin des Plantes of Paris, the pupil and worthy successor of Magendie. +His experiments in nerve physiology were begun in the first quarter of +the century, but his local experiments upon the brain itself were +not culminated until about 1842. At this time the old dispute over +phrenology had broken out afresh, and the studies of Flourens were +aimed, in part at least, at the strictly scientific investigation of +this troublesome topic. + +In the course of these studies Flourens discovered that in the medulla +oblongata, the part of the brain which connects that organ with the +spinal cord, there is a centre of minute size which cannot be injured in +the least without causing the instant death of the animal operated upon. +It may be added that it is this spot which is reached by the needle of +the garroter in Spanish executions, and that the same centre also is +destroyed when a criminal is "successfully" hanged, this time by the +forced intrusion of a process of the second cervical vertebra. Flourens +named this spot the "vital knot." Its extreme importance, as is now +understood, is due to the fact that it is the centre of nerves that +supply the heart; but this simple explanation, annulling the conception +of a specific "life centre," was not at once apparent. + +Other experiments of Flourens seemed to show that the cerebellum is the +seat of the centres that co-ordinate muscular activities, and that the +higher intellectual faculties are relegated to the cerebrum. But beyond +this, as regards localization, experiment faltered. Negative results, as +regards specific faculties, were obtained from all localized irritations +of the cerebrum, and Flourens was forced to conclude that the cerebral +lobe, while being undoubtedly the seat of higher intellection, performs +its functions with its entire structure. This conclusion, which +incidentally gave a quietus to phrenology, was accepted generally, and +became the stock doctrine of cerebral physiology for a generation. + +It will be seen, however, that these studies of Flourens had a double +bearing. They denied localization of cerebral functions, but they +demonstrated the localization of certain nervous processes in other +portions of the brain. On the whole, then, they spoke positively for the +principle of localization of function in the brain, for which a certain +number of students contended; while their evidence against cerebral +localization was only negative. There was here and there an observer who +felt that this negative testimony was not conclusive. In particular, +the German anatomist Meynert, who had studied the disposition of nerve +tracts in the cerebrum, was led to believe that the anterior portions of +the cerebrum must have motor functions in preponderance; the posterior +positions, sensory functions. Somewhat similar conclusions were reached +also by Dr. Hughlings-Jackson, in England, from his studies of epilepsy. +But no positive evidence was forthcoming until 1861, when Dr. Paul Broca +brought before the Academy of Medicine in Paris a case of brain lesion +which he regarded as having most important bearings on the question of +cerebral localization. + +The case was that of a patient at the Bicetre, who for twenty years had +been deprived of the power of speech, seemingly through loss of memory +of words. In 1861 this patient died, and an autopsy revealed that a +certain convolution of the left frontal lobe of his cerebrum had been +totally destroyed by disease, the remainder of his brain being intact. +Broca felt that this observation pointed strongly to a localization +of the memory of words in a definite area of the brain. Moreover, it +transpired that the case was not without precedent. As long ago as +1825 Dr. Boillard had been led, through pathological studies, to locate +definitely a centre for the articulation of words in the frontal lobe, +and here and there other observers had made tentatives in the same +direction. Boillard had even followed the matter up with pertinacity, +but the world was not ready to listen to him. Now, however, in the +half-decade that followed Broca's announcements, interest rose to +fever-beat, and through the efforts of Broca, Boillard, and numerous +others it was proved that a veritable centre having a strange +domination over the memory of articulate words has its seat in the third +convolution of the frontal lobe of the cerebrum, usually in the +left hemisphere. That part of the brain has since been known to the +English-speaking world as the convolution of Broca, a name which, +strangely enough, the discoverer's compatriots have been slow to accept. + +This discovery very naturally reopened the entire subject of brain +localization. It was but a short step to the inference that there must +be other definite centres worth the seeking, and various observers set +about searching for them. In 1867 a clew was gained by Eckhard, who, +repeating a forgotten experiment by Haller and Zinn of the previous +century, removed portions of the brain cortex of animals, with the +result of producing convulsions. But the really vital departure was +made in 1870 by the German investigators Fritsch and Hitzig, who, by +stimulating definite areas of the cortex of animals with a galvanic +current, produced contraction of definite sets of muscles of the +opposite side of the body. These most important experiments, received at +first with incredulity, were repeated and extended in 1873 by Dr. David +Ferrier, of London, and soon afterwards by a small army of independent +workers everywhere, prominent among whom were Franck and Pitres in +France, Munck and Goltz in Germany, and Horsley and Schafer in England. +The detailed results, naturally enough, were not at first all in +harmony. Some observers, as Goltz, even denied the validity of the +conclusions in toto. But a consensus of opinion, based on multitudes of +experiments, soon placed the broad general facts for which Fritsch and +Hitzig contended beyond controversy. It was found, indeed, that the +cerebral centres of motor activities have not quite the finality at +first ascribed to them by some observers, since it may often happen +that after the destruction of a centre, with attending loss of function, +there may be a gradual restoration of the lost function, proving that +other centres have acquired the capacity to take the place of the one +destroyed. There are limits to this capacity for substitution, however, +and with this qualification the definiteness of the localization of +motor functions in the cerebral cortex has become an accepted part of +brain physiology. + +Nor is such localization confined to motor centres. Later experiments, +particularly of Ferrier and of Munck, proved that the centres of vision +are equally restricted in their location, this time in the posterior +lobes of the brain, and that hearing has likewise its local habitation. +Indeed, there is every reason to believe that each form of primary +sensation is based on impressions which mainly come to a definitely +localized goal in the brain. But all this, be it understood, has no +reference to the higher forms of intellection. All experiment has proved +futile to localize these functions, except indeed to the extent of +corroborating the familiar fact of their dependence upon the brain, and, +somewhat problematically, upon the anterior lobes of the cerebrum in +particular. But this is precisely what should be expected, for the +clearer insight into the nature of mental processes makes it plain that +in the main these alleged "faculties" are not in themselves localized. +Thus, for example, the "faculty" of language is associated irrevocably +with centres of vision, of hearing, and of muscular activity, to go +no further, and only becomes possible through the association of these +widely separated centres. The destruction of Broca's centre, as was +early discovered, does not altogether deprive a patient of his knowledge +of language. He may be totally unable to speak (though as to this there +are all degrees of variation), and yet may comprehend what is said +to him, and be able to read, think, and even write correctly. Thus it +appears that Broca's centre is peculiarly bound up with the capacity for +articulate speech, but is far enough from being the seat of the faculty +of language in its entirety. + +In a similar way, most of the supposed isolated "faculties" of higher +intellection appear, upon clearer analysis, as complex aggregations of +primary sensations, and hence necessarily dependent upon numerous and +scattered centres. Some "faculties," as memory and volition, may be +said in a sense to be primordial endowments of every nerve cell--even +of every body cell. Indeed, an ultimate analysis relegates all +intellection, in its primordial adumbrations, to every particle of +living matter. But such refinements of analysis, after all, cannot hide +the fact that certain forms of higher intellection involve a pretty +definite collocation and elaboration of special sensations. Such +specialization, indeed, seems a necessary accompaniment of mental +evolution. That every such specialized function has its localized +centres of co-ordination, of some such significance as the demonstrated +centres of articulate speech, can hardly be in doubt--though this, be it +understood, is an induction, not as yet a demonstration. In other +words, there is every reason to believe that numerous "centres," in +this restricted sense, exist in the brain that have as yet eluded the +investigator. Indeed, the current conception regards the entire cerebral +cortex as chiefly composed of centres of ultimate co-ordination of +impressions, which in their cruder form are received by more primitive +nervous tissues--the basal ganglia, the cerebellum and medulla, and the +spinal cord. + +This, of course, is equivalent to postulating the cerebral cortex as +the exclusive seat of higher intellection. This proposition, however, +to which a safe induction seems to lead, is far afield from the +substantiation of the old conception of brain localization, which +was based on faulty psychology and equally faulty inductions from few +premises. The details of Gall's system, as propounded by generations of +his mostly unworthy followers, lie quite beyond the pale of scientific +discussion. Yet, as I have said, a germ of truth was there--the idea +of specialization of cerebral functions--and modern investigators have +rescued that central conception from the phrenological rubbish heap in +which its discoverer unfortunately left it buried. + + +THE MINUTE STRUCTURE OF THE BRAIN + +The common ground of all these various lines of investigations of +pathologist, anatomist, physiologist, physicist, and psychologist is, +clearly, the central nervous system--the spinal cord and the brain. +The importance of these structures as the foci of nervous and mental +activities has been recognized more and more with each new accretion +of knowledge, and the efforts to fathom the secrets of their intimate +structure has been unceasing. For the earlier students, only the +crude methods of gross dissections and microscopical inspection were +available. These could reveal something, but of course the inner secrets +were for the keener insight of the microscopist alone. And even for him +the task of investigation was far from facile, for the central nervous +tissues are the most delicate and fragile, and on many accounts the most +difficult of manipulation of any in the body. + +Special methods, therefore, were needed for this essay, and brain +histology has progressed by fitful impulses, each forward jet marking +the introduction of some ingenious improvement of mechanical technique, +which placed a new weapon in the hands of the investigators. + +The very beginning was made in 1824 by Rolando, who first thought of +cutting chemically hardened pieces of brain tissues into thin sections +for microscopical examination--the basal structure upon which almost all +the later advances have been conducted. Muller presently discovered that +bichromate of potassium in solution makes the best of fluids for the +preliminary preservation and hardening of the tissues. Stilling, in +1842, perfected the method by introducing the custom of cutting a series +of consecutive sections of the same tissue, in order to trace nerve +tracts and establish spacial relations. Then from time to time +mechanical ingenuity added fresh details of improvement. It was found +that pieces of hardened tissue of extreme delicacy can be made +better subject to manipulation by being impregnated with collodion or +celloidine and embedded in paraffine. Latterly it has become usual +to cut sections also from fresh tissues, unchanged by chemicals, by +freezing them suddenly with vaporized ether or, better, carbonic acid. +By these methods, and with the aid of perfected microtomes, the worker +of recent periods avails himself of sections of brain tissues of a +tenuousness which the early investigators could not approach. + +But more important even than the cutting of thin sections is the +process of making the different parts of the section visible, one tissue +differentiated from another. The thin section, as the early workers +examined it, was practically colorless, and even the crudest details of +its structure were made out with extreme difficulty. Remak did, indeed, +manage to discover that the brain tissue is cellular, as early as 1833, +and Ehrenberg in the same year saw that it is also fibrillar, but beyond +this no great advance was made until 1858, when a sudden impulse was +received from a new process introduced by Gerlach. The process itself +was most simple, consisting essentially of nothing more than the +treatment of a microscopical section with a solution of carmine. But the +result was wonderful, for when such a section was placed under the lens +it no longer appeared homogeneous. Sprinkled through its substance were +seen irregular bodies that had taken on a beautiful color, while the +matrix in which they were embedded remained unstained. In a word, the +central nerve cell had sprung suddenly into clear view. + +A most interesting body it proved, this nerve cell, or ganglion cell, +as it came to be called. It was seen to be exceedingly minute in size, +requiring high powers of the microscope to make it visible. It exists in +almost infinite numbers, not, however, scattered at random through the +brain and spinal cord. On the contrary, it is confined to those portions +of the central nervous masses which to the naked eye appear gray in +color, being altogether wanting in the white substance which makes up +the chief mass of the brain. Even in the gray matter, though sometimes +thickly distributed, the ganglion cells are never in actual contact one +with another; they always lie embedded in intercellular tissues, which +came to be known, following Virchow, as the neuroglia. + +Each ganglion cell was seen to be irregular in contour, and to have +jutting out from it two sets of minute fibres, one set relatively short, +indefinitely numerous, and branching in every direction; the other set +limited in number, sometimes even single, and starting out directly from +the cell as if bent on a longer journey. The numerous filaments came to +be known as protoplasmic processes; the other fibre was named, after its +discoverer, the axis cylinder of Deiters. It was a natural inference, +though not clearly demonstrable in the sections, that these filamentous +processes are the connecting links between the different nerve cells and +also the channels of communication between nerve cells and the periphery +of the body. The white substance of brain and cord, apparently, is made +up of such connecting fibres, thus bringing the different ganglion cells +everywhere into communication one with another. + +In the attempt to trace the connecting nerve tracts through this +white substance by either macroscopical or microscopical methods, most +important aid is given by a method originated by Waller in 1852. Earlier +than that, in 1839, Nasse had discovered that a severed nerve cord +degenerates in its peripheral portions. Waller discovered that every +nerve fibre, sensory or motor, has a nerve cell to or from which it +leads, which dominates its nutrition, so that it can only retain its +vitality while its connection with that cell is intact. Such cells he +named trophic centres. Certain cells of the anterior part of the spinal +cord, for example, are the trophic centres of the spinal motor nerves. +Other trophic centres, governing nerve tracts in the spinal cord itself, +are in the various regions of the brain. It occurred to Waller that +by destroying such centres, or by severing the connection at various +regions between a nervous tract and its trophic centre, sharply +defined tracts could be made to degenerate, and their location could +subsequently be accurately defined, as the degenerated tissues take on +a changed aspect, both to macroscopical and microscopical observation. +Recognition of this principle thus gave the experimenter a new weapon +of great efficiency in tracing nervous connections. Moreover, the same +principle has wide application in case of the human subject in disease, +such as the lesion of nerve tracts or the destruction of centres by +localized tumors, by embolisms, or by traumatisms. + +All these various methods of anatomical examination combine to make the +conclusion almost unavoidable that the central ganglion cells are the +veritable "centres" of nervous activity to which so many other lines of +research have pointed. The conclusion was strengthened by experiments +of the students of motor localization, which showed that the veritable +centres of their discovery lie, demonstrably, in the gray cortex of the +brain, not in the white matter. But the full proof came from pathology. +At the hands of a multitude of observers it was shown that in certain +well-known diseases of the spinal cord, with resulting paralysis, it is +the ganglion cells themselves that are found to be destroyed. Similarly, +in the case of sufferers from chronic insanities, with marked dementia, +the ganglion cells of the cortex of the brain are found to have +undergone degeneration. The brains of paretics in particular show such +degeneration, in striking correspondence with their mental decadence. +The position of the ganglion cell as the ultimate centre of nervous +activities was thus placed beyond dispute. + +Meantime, general acceptance being given the histological scheme of +Gerlach, according to which the mass of the white substance of the +brain is a mesh-work of intercellular fibrils, a proximal idea seemed +attainable of the way in which the ganglionic activities are correlated, +and, through association, built up, so to speak, into the higher mental +processes. Such a conception accorded beautifully with the ideas of +the associationists, who had now become dominant in psychology. But +one standing puzzle attended this otherwise satisfactory correlation +of anatomical observations and psychic analyses. It was this: Since, +according to the histologist, the intercellular fibres, along which +impulses are conveyed, connect each brain cell, directly or indirectly, +with every other brain cell in an endless mesh-work, how is it possible +that various sets of cells may at times be shut off from one another? +Such isolation must take place, for all normal ideation depends for +its integrity quite as much upon the shutting-out of the great mass of +associations as upon the inclusion of certain other associations. For +example, a student in solving a mathematical problem must for the moment +become quite oblivious to the special associations that have to do with +geography, natural history, and the like. But does histology give any +clew to the way in which such isolation may be effected? + +Attempts were made to find an answer through consideration of the very +peculiar character of the blood-supply in the brain. Here, as nowhere +else, the terminal twigs of the arteries are arranged in closed systems, +not anastomosing freely with neighboring systems. Clearly, then, a +restricted area of the brain may, through the controlling influence of +the vasomotor nerves, be flushed with arterial blood while neighboring +parts remain relatively anaemic. And since vital activities +unquestionably depend in part upon the supply of arterial blood, this +peculiar arrangement of the vascular mechanism may very properly be +supposed to aid in the localized activities of the central nervous +ganglia. But this explanation left much to be desired--in particular +when it is recalled that all higher intellection must in all probability +involve multitudes of widely scattered centres. + +No better explanation was forthcoming, however, until the year 1889, +when of a sudden the mystery was cleared away by a fresh discovery. +Not long before this the Italian histologist Dr. Camille Golgi had +discovered a method of impregnating hardened brain tissues with a +solution of nitrate of silver, with the result of staining the nerve +cells and their processes almost infinitely better than was possible by +the methods of Gerlach, or by any of the multiform methods that other +workers had introduced. Now for the first time it became possible to +trace the cellular prolongations definitely to their termini, for the +finer fibrils had not been rendered visible by any previous method +of treatment. Golgi himself proved that the set of fibrils known as +protoplasmic prolongations terminate by free extremities, and have no +direct connection with any cell save the one from which they spring. +He showed also that the axis cylinders give off multitudes of lateral +branches not hitherto suspected. But here he paused, missing the real +import of the discovery of which he was hard on the track. It remained +for the Spanish histologist Dr. S. Ramon y Cajal to follow up the +investigation by means of an improved application of Golgi's method of +staining, and to demonstrate that the axis cylinders, together with +all their collateral branches, though sometimes extending to a great +distance, yet finally terminate, like the other cell prolongations, in +arborescent fibrils having free extremities. In a word, it was shown +that each central nerve cell, with its fibrillar offshoots, is an +isolated entity. Instead of being in physical connection with a +multitude of other nerve cells, it has no direct physical connection +with any other nerve cell whatever. + +When Dr. Cajal announced his discovery, in 1889, his revolutionary +claims not unnaturally amazed the mass of histologists. There were some +few of them, however, who were not quite unprepared for the revelation; +in particular His, who had half suspected the independence of the cells, +because they seemed to develop from dissociated centres; and Forel, +who based a similar suspicion on the fact that he had never been able +actually to trace a fibre from one cell to another. These observers +then came readily to repeat Cajal's experiments. So also did the veteran +histologist Kolliker, and soon afterwards all the leaders everywhere. +The result was a practically unanimous confirmation of the Spanish +histologist's claims, and within a few months after his announcements +the old theory of union of nerve cells into an endless mesh-work was +completely discarded, and the theory of isolated nerve elements--the +theory of neurons, as it came to be called--was fully established in its +place. + +As to how these isolated nerve cells functionate, Dr. Cajal gave the +clew from the very first, and his explanation has met with universal +approval. + +In the modified view, the nerve cell retains its old position as the +storehouse of nervous energy. Each of the filaments jutting out from the +cell is held, as before, to be indeed a transmitter of impulses, but a +transmitter that operates intermittently, like a telephone wire that is +not always "connected," and, like that wire, the nerve fibril operates +by contact and not by continuity. Under proper stimulation the ends of +the fibrils reach out, come in contact with other end fibrils of other +cells, and conduct their destined impulse. Again they retract, and +communication ceases for the time between those particular cells. +Meantime, by a different arrangement of the various conductors, +different sets of cells are placed in communication, different +associations of nervous impulses induced, different trains of thought +engendered. Each fibril when retracted becomes a non-conductor, but when +extended and in contact with another fibril, or with the body of another +cell, it conducts its message as readily as a continuous filament could +do--precisely as in the case of an electric wire. + +This conception, founded on a most tangible anatomical basis, enables +us to answer the question as to how ideas are isolated, and also, as Dr. +Cajal points out, throws new light on many other mental processes. +One can imagine, for example, by keeping in mind the flexible nerve +prolongations, how new trains of thought may be engendered through novel +associations of cells; how facility of thought or of action in certain +directions is acquired through the habitual making of certain nerve-cell +connections; how certain bits of knowledge may escape our memory and +refuse to be found for a time because of a temporary incapacity of the +nerve cells to make the proper connections, and so on indefinitely. + +If one likens each nerve cell to a central telephone office, each of +its filamentous prolongations to a telephone wire, one can imagine a +striking analogy between the modus operandi of nervous processes and +of the telephone system. The utility of new connections at the central +office, the uselessness of the mechanism when the connections cannot +be made, the "wires in use" that retard your message, perhaps even the +crossing of wires, bringing you a jangle of sounds far different from +what you desire--all these and a multiplicity of other things that will +suggest themselves to every user of the telephone may be imagined as +being almost ludicrously paralleled in the operations of the nervous +mechanism. And that parallel, startling as it may seem, is not a mere +futile imagining. It is sustained and rendered plausible by a sound +substratum of knowledge of the anatomical conditions under which the +central nervous mechanism exists, and in default of which, as pathology +demonstrates with no less certitude, its functionings are futile to +produce the normal manifestations of higher intellection. + + + + +X. THE NEW SCIENCE OF ORIENTAL ARCHAEOLOGY + +HOW THE "RIDDLE OF THE SPHINX" WAS READ + +Conspicuously placed in the great hall of Egyptian antiquities in the +British Museum is a wonderful piece of sculpture known as the Rosetta +Stone. I doubt if any other piece in the entire exhibit attracts so much +attention from the casual visitor as this slab of black basalt on its +telescope-like pedestal. The hall itself, despite its profusion of +strangely sculptured treasures, is never crowded, but before this stone +you may almost always find some one standing, gazing with more or less +of discernment at the strange characters that are graven neatly across +its upturned, glass-protected face. A glance at this graven surface +suffices to show that three sets of inscriptions are recorded there. +The upper one, occupying about one-fourth of the surface, is a pictured +scroll, made up of chains of those strange outlines of serpents, hawks, +lions, and so on, which are recognized, even by the least initiated, +as hieroglyphics. The middle inscription, made up of lines, angles, +and half-pictures, one might surmise to be a sort of abbreviated +or short-hand hieroglyphic. The third or lower inscription is +Greek--obviously a thing of words. If the screeds above be also made of +words, only the elect have any way of proving the fact. + +Fortunately, however, even the least scholarly observer is left in +no doubt as to the real import of the thing he sees, for an obliging +English label tells us that these three inscriptions are renderings of +the same message, and that this message is a "decree of the priests +of Memphis conferring divine honors on Ptolemy V. (Epiphenes), King of +Egypt, B.C. 195." The label goes on to state that the upper inscription +(of which, unfortunately, only part of the last dozen lines or so +remains, the slab being broken) is in "the Egyptian language, in +hieroglyphics, or writing of the priests"; the second inscription "in +the same language is in Demotic, or the writing of the people"; and +the third "the Greek language and character." Following this is a brief +biography of the Rosetta Stone itself, as follows: "The stone was found +by the French in 1798 among the ruins of Fort Saint Julien, near the +Rosetta mouth of the Nile. It passed into the hands of the British by +the treaty of Alexandria, and was deposited in the British Museum in +the year 1801." There is a whole volume of history in that brief +inscription--and a bitter sting thrown in, if the reader chance to be +a Frenchman. Yet the facts involved could scarcely be suggested more +modestly. They are recorded much more bluntly in a graven inscription +on the side of the stone, which reads: "Captured in Egypt by the British +Army, 1801." No Frenchman could read those words without a veritable +sinking of the heart. + +The value of the Rosetta Stone depended on the fact that it gave +promise, even when casually inspected, of furnishing a key to the +centuries-old mystery of the hieroglyphics. For two thousand years the +secret of these strange markings had been forgotten. Nowhere in the +world--quite as little in Egypt as elsewhere--had any man the slightest +clew to their meaning; there were those who even doubted whether these +droll picturings really had any specific meaning, questioning whether +they were not rather vague symbols of esoteric religious import and +nothing more. And it was the Rosetta Stone that gave the answer to +these doubters and restored to the world a lost language and a forgotten +literature. + +The trustees of the museum recognized at once that the problem of the +Rosetta Stone was one on which the scientists of the world might well +exhaust their ingenuity, and promptly published to the world a carefully +lithographed copy of the entire inscription, so that foreign scholarship +had equal opportunity with the British to try at the riddle. It was an +Englishman, however, who first gained a clew to the solution. This was +none other than the extraordinary Dr. Thomas Young, the demonstrator of +the vibratory nature of light. + +Young's specific discoveries were these: (1) That many of the pictures +of the hieroglyphics stand for the names of the objects actually +delineated; (2) that other pictures are sometimes only symbolic; (3) +that plural numbers are represented by repetition; (4) that numerals are +represented by dashes; (5) that hieroglyphics may read either from +the right or from the left, but always from the direction in which the +animal and human figures face; (6) that proper names are surrounded by +a graven oval ring, making what he called a cartouche; (7) that the +cartouches of the preserved portion of the Rosetta Stone stand for the +name of Ptolemy alone; (8) that the presence of a female figure after +such cartouches in other inscriptions always denotes the female sex; (9) +that within the cartouches the hieroglyphic symbols have a positively +phonetic value, either alphabetic or syllabic; and (10) that several +different characters may have the same phonetic value. + +Just what these phonetic values are Young pointed out in the case of +fourteen characters representing nine sounds, six of which are accepted +to-day as correctly representing the letters to which he ascribed them, +and the three others as being correct regarding their essential or +consonant element. It is clear, therefore, that he was on the right +track thus far, and on the very verge of complete discovery. But, +unfortunately, he failed to take the next step, which would have been to +realize that the same phonetic values which were given to the alphabetic +characters within the cartouches were often ascribed to them also when +used in the general text of an inscription; in other words, that the +use of an alphabet was not confined to proper names. This was the great +secret which Young missed and which his French successor, Jean Francois +Champollion, working on the foundation that Young had laid, was enabled +to ferret out. + +Young's initial studies of the Rosetta Stone were made in 1814; his +later publication bore date of 1819. Champollion's first announcement of +results came in 1822; his second and more important one in 1824. By this +time, through study of the cartouches of other inscriptions, Champollion +had made out almost the complete alphabet, and the "riddle of the +Sphinx" was practically solved. He proved that the Egyptians had +developed a relatively complete alphabet (mostly neglecting the vowels, +as early Semitic alphabets did also) centuries before the Phoenicians +were heard of in history. What relation this alphabet bore to the +Phoenician we shall have occasion to ask in another connection; for the +moment it suffices to know that those strange pictures of the Egyptian +scroll are really letters. + +Even this statement, however, must be in a measure modified. These +pictures are letters and something more. Some of them are purely +alphabetical in character and some are symbolic in another way. +Some characters represent syllables. Others stand sometimes as mere +representatives of sounds, and again, in a more extended sense, as +representations of things, such as all hieroglyphics doubtless were +in the beginning. In a word, this is an alphabet, but not a perfected +alphabet, such as modern nations are accustomed to; hence the enormous +complications and difficulties it presented to the early investigators. + +Champollion did not live to clear up all these mysteries. His work was +taken up and extended by his pupil Rossellini, and in particular by Dr. +Richard Lepsius in Germany, followed by M. Bernouf, and by Samuel +Birch of the British Museum, and more recently by such well-known +Egyptologists as MM. Maspero and Mariette and Chabas, in France, Dr. +Brugsch, in Germany, and Dr. E. Wallis Budge, the present head of the +Department of Oriental Antiquities at the British Museum. But the +task of later investigators has been largely one of exhumation and +translation of records rather than of finding methods. + + +TREASURES FROM NINEVEH + +The most casual wanderer in the British Museum can hardly fail to notice +two pairs of massive sculptures, in the one case winged bulls, in the +other winged lions, both human-headed, which guard the entrance to the +Egyptian hall, close to the Rosetta Stone. Each pair of these weird +creatures once guarded an entrance to the palace of a king in the famous +city of Nineveh. As one stands before them his mind is carried back over +some twenty-seven intervening centuries, to the days when the "Cedar of +Lebanon" was "fair in his greatness" and the scourge of Israel. + +The very Sculptures before us, for example, were perhaps seen by Jonah +when he made that famous voyage to Nineveh some seven or eight hundred +years B.C. A little later the Babylonian and the Mede revolted against +Assyrian tyranny and descended upon the fair city of Nineveh, and almost +literally levelled it to the ground. But these great sculptures, among +other things, escaped destruction, and at once hidden and preserved by +the accumulating debris of the centuries, they stood there age after +age, their very existence quite forgotten. When Xenophon marched past +their site with the ill-starred expedition of the ten thousand, in the +year 400 B.C., he saw only a mound which seemed to mark the site of some +ancient ruin; but the Greek did not suspect that he looked upon the site +of that city which only two centuries before had been the mistress of +the world. + +So ephemeral is fame! And yet the moral scarcely holds in the sequel; +for we of to-day, in this new, undreamed-of Western world, behold these +mementos of Assyrian greatness fresh from their twenty-five hundred +years of entombment, and with them records which restore to us the +history of that long-forgotten people in such detail as it was not known +to any previous generation since the fall of Nineveh. For two thousand +five hundred years no one saw these treasures or knew that they existed. +One hundred generations of men came and went without once pronouncing +the name of kings Shalmaneser or Asumazirpal or Asurbanipal. And to-day, +after these centuries of oblivion, these names are restored to +history, and, thanks to the character of their monuments, are assured a +permanency of fame that can almost defy time itself. It would be nothing +strange, but rather in keeping with their previous mutations of fortune, +if the names of Asurnazirpal and Asurbanipal should be familiar as +household words to future generations that have forgotten the existence +of an Alexander, a Caesar, and a Napoleon. For when Macaulay's +prospective New Zealander explores the ruins of the British Museum +the records of the ancient Assyrians will presumably still be there +unscathed, to tell their story as they have told it to our generation, +though every manuscript and printed book may have gone the way of +fragile textures. + +But the past of the Assyrian sculptures is quite necromantic enough +without conjuring for them a necromantic future. The story of their +restoration is like a brilliant romance of history. Prior to the middle +of this century the inquiring student could learn in an hour or so all +that was known in fact and in fable of the renowned city of Nineveh. He +had but to read a few chapters of the Bible and a few pages of Diodorus +to exhaust the important literature on the subject. If he turned also to +the pages of Herodotus and Xenophon, of Justin and Aelian, these served +chiefly to confirm the suspicion that the Greeks themselves knew almost +nothing more of the history of their famed Oriental forerunners. The +current fables told of a first King Ninus and his wonderful queen +Semiramis; of Sennacherib the conqueror; of the effeminate Sardanapalus, +who neglected the warlike ways of his ancestors but perished gloriously +at the last, with Nineveh itself, in a self-imposed holocaust. And that +was all. How much of this was history, how much myth, no man could say; +and for all any one suspected to the contrary, no man could ever know. +And to-day the contemporary records of the city are before us in such +profusion as no other nation of antiquity, save Egypt alone, can at all +rival. Whole libraries of Assyrian books are at hand that were written +in the seventh century before our era. These, be it understood, are the +original books themselves, not copies. The author of that remote time +appeals to us directly, hand to eye, without intermediary transcriber. +And there is not a line of any Hebrew or Greek manuscript of a like age +that has been preserved to us; there is little enough that can match +these ancient books by a thousand years. When one reads Moses or +Isaiah, Homer, Hesiod, or Herodotus, he is but following the +transcription--often unquestionably faulty and probably never in all +parts perfect--of successive copyists of later generations. The oldest +known copy of the Bible, for example, dates probably from the fourth +century A.D., a thousand years or more after the last Assyrian records +were made and read and buried and forgotten. + +There was at least one king of Assyria--namely, Asurbanipal, whose +palace boasted a library of some ten thousand volumes--a library, if you +please, in which the books were numbered and shelved systematically, and +classified and cared for by an official librarian. If you would see some +of the documents of this marvellous library you have but to step past +the winged lions of Asurnazirpal and enter the Assyrian hall just around +the corner from the Rosetta Stone. Indeed, the great slabs of stone from +which the lions themselves are carved are in a sense books, inasmuch as +there are written records inscribed on their surface. A glance reveals +the strange characters in which these records are written, graven neatly +in straight lines across the stone, and looking to casual inspection +like nothing so much as random flights of arrow-heads. The resemblance +is so striking that this is sometimes called the arrow-head character, +though it is more generally known as the wedge or cuneiform character. +The inscriptions on the flanks of the lions are, however, only makeshift +books. But the veritable books are no farther away than the next room +beyond the hall of Asurnazirpal. They occupy part of a series of cases +placed down the centre of this room. Perhaps it is not too much to speak +of this collection as the most extraordinary set of documents of all the +rare treasures of the British Museum, for it includes not books alone, +but public and private letters, business announcements, marriage +contracts--in a word, all the species of written records that enter into +the every-day life of an intelligent and cultured community. + +But by what miracle have such documents been preserved through all these +centuries? A glance makes the secret evident. It is simply a case of +time-defying materials. Each one of these Assyrian documents appears to +be, and in reality is, nothing more or less than an inscribed fragment +of brick, having much the color and texture of a weathered terra-cotta +tile of modern manufacture. These slabs are usually oval or oblong in +shape, and from two or three to six or eight inches in length and +an inch or so in thickness. Each of them was originally a portion of +brick-clay, on which the scribe indented the flights of arrowheads +with some sharp-cornered instrument, after which the document was made +permanent by baking. They are somewhat fragile, of course, as all bricks +are, and many of them have been more or less crumbled in the destruction +of the palace at Nineveh; but to the ravages of mere time they are as +nearly invulnerable as almost anything in nature. Hence it is that these +records of a remote civilization have been preserved to us, while the +similar records of such later civilizations as the Grecian have utterly +perished, much as the flint implements of the cave-dweller come to +us unchanged, while the iron implements of a far more recent age have +crumbled away. + + +HOW THE RECORDS WERE READ + +After all, then, granted the choice of materials, there is nothing so +very extraordinary in the mere fact of preservation of these ancient +records. To be sure, it is vastly to the credit of nineteenth-century +enterprise to have searched them out and brought them back to light. +But the real marvel in connection with them is the fact that +nineteenth-century scholarship should have given us, not the material +documents themselves, but a knowledge of their actual contents. The +flight of arrow-heads on wall or slab or tiny brick have surely a +meaning; but how shall we guess that meaning? These must be words; but +what words? The hieroglyphics of the Egyptians were mysterious enough +in all conscience; yet, after all, their symbols have a certain +suggestiveness, whereas there is nothing that seems to promise a mental +leverage in the unbroken succession of these cuneiform dashes. Yet the +Assyrian scholar of to-day can interpret these strange records almost +as readily and as surely as the classical scholar interprets a +Greek manuscript. And this evidences one of the greatest triumphs of +nineteenth-century scholarship, for within almost two thousand years no +man has lived, prior to our century, to whom these strange inscriptions +would not have been as meaningless as they are to the most casual +stroller who looks on them with vague wonderment here in the museum +to-day. For the Assyrian language, like the Egyptian, was veritably a +dead language; not, like Greek and Latin, merely passed from practical +every-day use to the closet of the scholar, but utterly and absolutely +forgotten by all the world. Such being the case, it is nothing less than +marvellous that it should have been restored. + +It is but fair to add that this restoration probably never would have +been effected, with Assyrian or with Egyptian, had the language in dying +left no cognate successor; for the powers of modern linguistry, though +great, are not actually miraculous. But, fortunately, a language once +developed is not blotted out in toto; it merely outlives its usefulness +and is gradually supplanted, its successor retaining many traces of its +origin. So, just as Latin, for example, has its living representatives +in Italian and the other Romance tongues, the language of Assyria is +represented by cognate Semitic languages. As it chances, however, these +have been of aid rather in the later stages of Assyrian study than at +the very outset; and the first clew to the message of the cuneiform +writing came through a slightly different channel. + +Curiously enough, it was a trilingual inscription that gave the clew, as +in the case of the Rosetta Stone, though with very striking difference +withal. The trilingual inscription now in question, instead of being +a small, portable monument, covers the surface of a massive bluff at +Behistun in western Persia. Moreover, all three of its inscriptions +are in cuneiform characters, and all three are in languages that at +the beginning of our century were absolutely unknown. This inscription +itself, as a striking monument of unknown import, had been seen by +successive generations. Tradition ascribed it, as we learn from Ctesias, +through Diodorus, to the fabled Assyrian queen Semiramis. Tradition +was quite at fault in this; but it is only recently that knowledge has +availed to set it right. The inscription, as is now known, was really +written about the year 515 B.C., at the instance of Darius I., King of +Persia, some of whose deeds it recounts in the three chief languages of +his widely scattered subjects. + +The man who at actual risk of life and limb copied this wonderful +inscription, and through interpreting it became the veritable "father of +Assyriology," was the English general Sir Henry Rawlinson. His feat was +another British triumph over the same rivals who had competed for +the Rosetta Stone; for some French explorers had been sent by their +government, some years earlier, expressly to copy this strange record, +and had reported that it was impossible to reach the inscription. But +British courage did not find it so, and in 1835 Rawlinson scaled the +dangerous height and made a paper cast of about half the inscription. +Diplomatic duties called him away from the task for some years, but +in 1848 he returned to it and completed the copy of all parts of the +inscription that have escaped the ravages of time. And now the material +was in hand for a new science, which General Rawlinson himself soon, +assisted by a host of others, proceeded to elaborate. + +The key to the value of this unique inscription lies in the fact that +its third language is ancient Persian. It appears that the ancient +Persians had adopted the cuneiform character from their western +neighbors, the Assyrians, but in so doing had made one of those +essential modifications and improvements which are scarcely possible to +accomplish except in the transition from one race to another. Instead +of building with the arrow-head a multitude of syllabic characters, +including many homophones, as had been and continued to be the custom +with the Assyrians, the Persians selected a few of these characters and +ascribed to them phonetic values that were almost purely alphabetic. In +a word, while retaining the wedge as the basal stroke of their script, +they developed an alphabet, making the last wonderful analysis of +phonetic sounds which even to this day has escaped the Chinese, which +the Egyptians had only partially effected, and which the Phoenicians +were accredited by the Greeks with having introduced to the Western +world. In addition to this all-essential step, the Persians had +introduced the minor but highly convenient custom of separating the +words of a sentence from one another by a particular mark, differing +in this regard not only from the Assyrians and Egyptians, but from the +early Greek scribes as well. + +Thanks to these simplifications, the old Persian language had been +practically restored about the beginning of the nineteenth century, +through the efforts of the German Grotefend, and further advances in +it were made just at this time by Renouf, in France, and by Lassen, in +Germany, as well as by Rawlinson himself, who largely solved the problem +of the Persian alphabet independently. So the Persian portion of the +Behistun inscription could be at least partially deciphered. This +in itself, however, would have been no very great aid towards the +restoration of the languages of the other portions had it not chanced, +fortunately, that the inscription is sprinkled with proper names. Now +proper names, generally speaking, are not translated from one language +to another, but transliterated as nearly as the genius of the language +will permit. It was the fact that the Greek word Ptolemaics was +transliterated on the Rosetta Stone that gave the first clew to the +sounds of the Egyptian characters. Had the upper part of the Rosetta +Stone been preserved, on which, originally, there were several other +names, Young would not have halted where he did in his decipherment. + +But fortune, which had been at once so kind and so tantalizing in the +case of the Rosetta Stone, had dealt more gently with the Behistun +inscriptions; for no fewer than ninety proper names were preserved +in the Persian portion and duplicated, in another character, in the +Assyrian inscription. A study of these gave a clew to the sounds of the +Assyrian characters. The decipherment of this character, however, even +with this aid, proved enormously difficult, for it was soon evident that +here it was no longer a question of a nearly perfect alphabet of a few +characters, but of a syllabary of several hundred characters, including +many homophones, or different forms for representing the same sound. +But with the Persian translation for a guide on the one hand, and the +Semitic languages, to which family the Assyrian belonged, on the other, +the appalling task was gradually accomplished, the leading investigators +being General Rawlinson, Professor Hincks, and Mr. Fox-Talbot, in +England, Professor Jules Oppert, in Paris, and Professor Julian +Schrader, in Germany, though a host of other scholars soon entered the +field. + +This great linguistic feat was accomplished about the middle of the +nineteenth century. But so great a feat was it that many scholars of the +highest standing, including Joseph Erneste Renan, in France, and Sir G. +Cornewall Lewis, in England, declined at first to accept the results, +contending that the Assyriologists had merely deceived themselves by +creating an arbitrary language. The matter was put to a test in 1855 +at the suggestion of Mr. Fox-Talbot, when four scholars, one being Mr. +Talbot himself and the others General Rawlinson, Professor Hincks, +and Professor Oppert, laid before the Royal Asiatic Society their +independent interpretations of a hitherto untranslated Assyrian text. A +committee of the society, including England's greatest historian of the +century, George Grote, broke the seals of the four translations, and +reported that they found them unequivocally in accord as regards their +main purport, and even surprisingly uniform as regards the phraseology +of certain passages--in short, as closely similar as translations from +the obscure texts of any difficult language ever are. This decision gave +the work of the Assyriologists official status, and the reliability of +their method has never since been in question. Henceforth Assyriology +was an established science. + + + + +APPENDIX + + REFERENCE-LIST + + CHAPTER I. MODERN DEVELOPMENT OF THE PHYSICAL SCIENCES + + (1) Robert Boyle, Philosophical Works (3 vols.). London, 1738. + + CHAPTER II. THE BEGINNINGS OF MODERN CHEMISTRY + + (1) For a complete account of the controversy called the "Water + Controversy," see The Life of the Hon. Henry Cavendish, by George + Wilson, M.D., F.R.S.E. London, 1850. + + (2) Henry Cavendish, in Phil. Trans. for 1784, P. 119. + + (3) Lives of the Philosophers of the Time of George III., by Henry, Lord + Brougham, F.R.S., p. 106. London, 1855. + + (4) Experiments and Observations on Different Kinds of Air, by Joseph + Priestley (3 vols.). Birmingham, 790, vol. II, pp. 103-107. + + (5) Lectures on Experimental Philosophy, by Joseph Priestley, lecture + IV., pp. 18, ig. J. Johnson, London, 1794. + + (6) Translated from Scheele's Om Brunsten, eller Magnesia, och dess + Egenakaper. Stockholm, 1774, and published as Alembic Club Reprints, No. + 13, 1897, p. 6. + + (7) According to some writers this was discovered by Berzelius. + + (8) Histoire de la Chimie, par Ferdinand Hoefer. Paris, 1869, Vol. CL, + p. 289. + + (9) Elements of Chemistry, by Anton Laurent Lavoisier, translated by + Robert Kerr, p. 8. London and Edinburgh, 1790. + + (10) Ibid., pp. 414-416. + + CHAPTER III. CHEMISTRY SINCE THE TIME OF DALTON + + (1) Sir Humphry Davy, in Phil. Trans., Vol. VIII. + + CHAPTER IV. ANATOMY AND PHYSIOLOGY IN THE EIGHTEENTH CENTURY + + (1) Baas, History of Medicine, p. 692. + + (2) Based on Thomas H. Huxley's Presidential Address to the British + Association for the Advancement of Science, 1870. + + (3) Essays on Digestion, by James Carson. London, 1834, p. 6. + + (4) Ibid., p. 7. + + (5) John Hunter, On the Digestion of the Stomach after Death, first + edition, pp. 183-188. + + (6) Erasmus Darwin, The Botanic Garden, pp. 448-453. London, 1799. + + CHAPTER V. ANATOMY AND PHYSIOLOGY IN THE NINETEENTH CENTURY + + (1) Baron de Cuvier's Theory of the Earth. New York, 1818, p. 123. + + (2) On the Organs and Mode of Fecundation of Orchidex and Asclepiadea, + by Robert Brown, Esq., in Miscellaneous Botanical Works. London, 1866, + Vol. I., pp. 511-514. + + (3) Justin Liebig, Animal Chemistry. London, 1843, p. 17f. + + CHAPTER VI. THEORIES OF ORGANIC EVOLUTION + + (1) "Essay on the Metamorphoses of Plants," by Goethe, translated + for the present work from Grundriss einer Geschichte der + Naturwissenschaften, by Friederich Dannemann (2 vols.). Leipzig, 1896, + Vol. I., p. 194. + + (2) The Temple of Nature, or The Origin of Society, by Erasmus Darwin, + edition published in 1807, p. 35. + + (3) Baron de Cuvier, Theory of the Earth. New York, 1818, p.74. (This + was the introduction to Cuvier's great work.) + + (4) Robert Chambers, Explanations: a sequel to Vestiges of Creation. + London, Churchill, 1845, pp. 148-153. + + CHAPTER VII. EIGHTEENTH-CENTURY MEDICINE + + (1) Condensed from Dr. Boerhaave's Academical Lectures on the Theory of + Physic. London, 1751, pp. 77, 78. Boerhaave's lectures were published as + Aphorismi de cognoscendis et curandis Morbis, Leyden, 1709. On this + book Van Swieten wrote commentaries filling five volumes. Another very + celebrated work of Boerhaave is his Institutiones et Experimenta + Chemic, Paris, 1724, the germs of this being given as a lecture on his + appointment to the chair of chemistry in the University of Leyden in + 1718. + + (2) An Inquiry into the Causes and Effects of the Variola Vaccine, etc., + by Edward Jenner, M.D., F.R.S., etc. London, 1799, pp. 2-7. He wrote + several other papers, most of which were communications to the Royal + Society. His last publication was, On the Influence of Artificial + Eruptions in Certain Diseases (London, 1822), a subject to which he had + given much time and study. + + CHAPTER VIII. NINETEENTH-CENTURY MEDICINE + + (1) In the introduction to Corvisart's translation of Avenbrugger's + work. Paris, 1808. + + (2) Laennec, Traite d'Auscultation Mediate. Paris, 1819. This was + Laennec's chief work, and was soon translated into several different + languages. Before publishing this he had written also, Propositions sur + la doctrine midicale d'Hippocrate, Paris, 1804, and Memoires sur les + vers visiculaires, in the same year. + + (3) Researches, Chemical and Philosophical, chiefly concerning Nitrous + Oxide or Dephlogisticated Nitrous Air and its Respiration, by Humphry + Davy. London, 1800, pp. 479-556. + + (4) Ibid. + + (5) For accounts of the discovery of anaesthesia, see Report of the + Board of Trustees of the Massachusetts General Hospital, Boston, 1888. + Also, The Ether Controversy: Vindication of the Hospital Reports of + 1848, by N. L Bowditch, Boston, 1848. An excellent account is given in + Littell's Living Age, for March, 1848, written by R. H. Dana, Jr. There + are also two Congressional Reports on the question of the discovery of + etherization, one for 1848, the other for 11852. + + (6) Simpson made public this discovery of the anaesthetic properties + of chloroform in a paper read before the Medico-Chirurgical Society of + Edinburgh, in March, 1847, about three months after he had first seen + a surgical operation performed upon a patient to whom ether had been + administered. + + (7) Louis Pasteur, Studies on Fermentation. London, 1870. + + (8) Louis Pasteur, in Comptes Rendus des Sciences de L'Academie des + Sciences, vol. XCII., 1881, pp. 429-435. + + CHAPTER IX. THE NEW SCIENCE OF EXPERIMENTAL PSYCHOLOGY + + (1) Bell's communications were made to the Royal Society, but his + studies and his discoveries in the field of anatomy of the nervous + system were collected and published, in 1824, as An Exposition of the + Natural System of Nerves of the Human Body: being a Republication of the + Papers delivered to the Royal Society on the Subject of the Nerves. + + (2) Marshall Hall, M.D., F.R.S.L., On the Reflex Functions of the + Medulla Oblongata and the Medulla Spinalis, in Phil. Trans. of Royal + Soc., vol. XXXIII., 1833. + + + + + + +End of the Project Gutenberg EBook of A History of Science, Volume 4(of 5), by +Henry Smith Williams + +*** END OF THIS PROJECT GUTENBERG EBOOK HISTORY OF SCIENCE, V4 *** + +***** This file should be named 1708.txt or 1708.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/1/7/0/1708/ + +Produced by Charles Keller + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions 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. 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