It was at this point, and while the inquiries of geologists, notwithstanding their value, were still crude and unsettled, that the subject was taken up by Cuvier, one of the greatest naturalists Europe has ever produced. A few others there are who have surpassed him in depth; but in comprehensiveness it would be hard to find his superior; and the immense range of his studies gave him a peculiar advantage in surveying the operations and dependencies of the external world.[1074] This remarkable man is unquestionably the founder of geology as a science, since he is not only the first who saw the necessity of bringing to bear upon it the generalizations of comparative anatomy, but he is also the first who actually, executing this great idea, succeeded in coördinating the study of the strata of the earth with the study of the fossil animals found in them.[1075] Shortly before his researches were published, many valuable facts had indeed been collected respecting the separate strata; the primary formations being investigated by the Germans, the secondary ones by the English.[1076] But these observations, notwithstanding their merit, were isolated; and they lacked that vast conception which gave unity and grandeur to the whole, by connecting inquiries concerning the inorganic changes of the surface of the globe with other inquiries concerning the organic changes of the animals the surface contained.
How completely this immense step is due to France, is evident not only from the part played by Cuvier, but also from the admitted fact, that to the French we owe our knowledge respecting tertiary strata,[1077] in which the organic remains are most numerous, and the general analogy to our present state is most intimate.[1078] Another circumstance may likewise be added, as pointing to the same conclusion. This is, that the first application of the principles of comparative anatomy to the study of fossil bones was also the work of a Frenchman, the celebrated Daubenton. Hitherto these bones had been the object of stupid wonder; some saying that they were rained from heaven, others saying that they were the gigantic limbs of the ancient patriarchs, men who were believed to be tall because they were known to be old.[1079] Such idle conceits were for ever destroyed by Daubenton, in a Memoir he published in 1762;[1080] with which, however, we are not now concerned, except that it is evidence of the state of the French mind, and is worth noting as a precursor of the discoveries of Cuvier.
By this union of geology and anatomy, there was first introduced into the study of nature a clear conception of the magnificent doctrine of universal change; while at the same time there grew up by its side a conception equally steady of the regularity with which the changes are accomplished, and of the undeviating laws by which they are governed. Similar ideas had no doubt been occasionally held in preceding ages; but the great Frenchmen of the eighteenth century were the first who applied them to the entire structure of the globe, and who thus prepared the way for that still higher view for which their minds were not yet ripe,[1081] but to which in our own time the most advanced thinkers are rapidly rising. For it is now beginning to be understood, that since every addition to knowledge affords fresh proof of the regularity with which all the changes of nature are conducted, we are bound to believe that the same regularity existed long before our little planet assumed its present form, and long before man trod the surface of the earth. We have the most abundant evidence that the movements incessantly occurring in the material world have a character of uniformity; and this uniformity is so clearly marked, that in astronomy, the most perfect of all the sciences, we are able to predict events many years before they actually happen; nor can any one doubt, that if on other subjects our science were equally advanced, our predictions would be equally accurate. It is, therefore, clear, that the burden of proof lies not on those who assert the eternal regularity of nature, but rather on those who deny it; and who set up an imaginary period, to which they assign an imaginary catastrophe, during which they say new laws were introduced and a new order established. Such gratuitous assumptions, even if they eventually turn out to be true, are in the present state of knowledge unwarrantable, and ought to be rejected, as the last remains of those theological prejudices by which the march of every science has in its turn been hindered. These and all analagous notions work a double mischief. They are mischievous, because they cripple the human mind by imposing limits to its inquiries; and above all they are mischievous, because they weaken that vast conception of continuous and uninterrupted law, which few indeed are able firmly to seize, but on which the highest generalizations of future science must ultimately depend.
It is this deep conviction, that changing phenomena have unchanging laws, and that there are principles of order to which all apparent disorder may be referred,—it is this, which, in the seventeenth century, guided in a limited field Bacon, Descartes, and Newton; which in the eighteenth century was applied to every part of the material universe; and which it is the business of the nineteenth century to extend to the history of the human intellect. This last department of inquiry we owe chiefly to Germany; for, with the single exception of Vico, no one even suspected the possibility of arriving at complete generalizations respecting the progress of man, until shortly before the French Revolution, when the great German thinkers began to cultivate this, the highest and most difficult of all studies. But the French themselves were too much occupied with physical science to pay attention to such matters;[1082] and speaking generally, we may say that, in the eighteenth century, each of the three leading nations of Europe had a separate part to play. England diffused a love of freedom; France, a knowledge of physical science; while Germany, aided in some degree by Scotland, revived the study of metaphysics, and created the study of philosophic history. To this classification some exceptions may of course be made; but that these were the marked characteristics of the three countries, is certain. After the death of Locke in 1704, and that of Newton in 1727, there was in England a singular dearth of great speculative thinkers; and this not because the ability was wanting, but because it was turned partly into practical pursuits, partly into political contests. I shall hereafter examine the causes of this peculiarity, and endeavour to ascertain the extent to which it has influenced the fortunes of the country. That the results were, on the whole, beneficial, I entertain no doubt; but they were unquestionably injurious to the progress of science, because they tended to divert it from all new truths, except those likely to produce obvious and practical benefit. The consequence was, that though the English made several great discoveries, they did not possess, during seventy years, a single man who took a really comprehensive view of the phenomena of nature; not one who could be compared with those illustrious thinkers who in France reformed every branch of physical knowledge. Nor was it until more than two generations after the death of Newton, that the first symptoms appeared of a remarkable reaction, which quickly displayed itself in nearly every department of the national intellect. In physics, it is enough to mention Dalton, Davy, and Young, each of whom was in his own field the founder of a new epoch; while on other subjects I can only just refer, first, to the influence of the Scotch school; and, secondly, to that sudden and well-deserved admiration for the German literature of which Coleridge was the principal exponent, and which infused into the English mind a taste for generalizations higher and more fearless than any hitherto known. The history of this vast movement, which began early in the nineteenth century, will be traced in the future volumes of this work: at present I merely notice it, as illustrating the fact, that until the movement began, the English, though superior to the French in several matters of extreme importance, were for many years inferior to them in those large and philosophic views, without which not only is the most patient industry of no avail, but even real discoveries lose their proper value, for want of such habits of generalization as would trace their connexion with each other, and consolidate their severed fragments into one vast system of complete and harmonious truth.
The interest attached to these inquiries has induced me to treat them at greater length than I had intended; perhaps at greater length than is suitable to the suggestive and preparatory character of this Introduction. But the extraordinary success with which the French now cultivated physical knowledge is so curious, on account of its connexion with the Revolution, that I must mention a few more of its most prominent instances: though, for the sake of brevity, I will confine myself to those three great divisions which, when put together, form what is called Natural History, and in all of which we shall see that the most important steps were taken in France during the latter half of the eighteenth century.
In the first of these divisions, namely, the department of zoology, we owe to the Frenchmen of the eighteenth century those generalizations which are still the highest this branch of knowledge has reached. Taking zoology in the proper sense of the term, it consists only of two parts, the anatomical part, which is its statics, and the physiological part, which is its dynamics: the first referring to the structure of animals; the other, to their functions.[1083] Both of these were worked out, nearly at the same time, by Cuvier and Bichat; and the leading conclusions at which they arrived, remain, after the lapse of sixty years, undisturbed in their essential points. In 1795, Cuvier laid down the great principle, that the study and classification of animals was to be, not as heretofore, with a view to external peculiarities, but with a view to internal organization; and that, therefore, no real advance could be made in our knowledge except by extending the boundaries of comparative anatomy.[1084] This step, simple as it now appears, was of immense importance, since by it zoology was at once rescued from the hands of the observer, and thrown into those of the experimenter: the consequence of which has been the attainment of that precision and accuracy of detail, which experiment alone can give, and which is every way superior to such popular facts as observation supplies. By thus indicating to naturalists the true path of inquiry, by accustoming them to a close and severe method, and by teaching them to despise those vague descriptions in which they had formerly delighted, Cuvier laid the foundation of a progress which, during the last sixty years, has surpassed the most sanguine expectations. This, then, is the real service rendered by Cuvier, that he overthrew the artificial system which the genius of Linnæus had raised up,[1085] and substituted in its place that far superior scheme which gave the freest scope to future inquiry; since, according to it, all systems are to be deemed imperfect and provisional so long as any thing remains to be learned respecting the comparative anatomy of the animal kingdom. The influence exercised by this great view was increased by the extraordinary skill and industry with which its proposer followed it out, and proved the practicability of his own precepts. His additions to our knowledge of comparative anatomy are probably more numerous than those made by any other man; but what has gained him most celebrity is, the comprehensive spirit with which he used what he acquired. Independently of other generalizations, he is the author of that vast classification of the whole animal kingdom into vertebrata, mollusca, articulata, and radiata;[1086] a classification which keeps its ground, and is one of the most remarkable instances of that large and philosophic spirit which France brought to bear upon the phenomena of the material world.[1087]
Great, however, as is the name of Cuvier, a greater still remains behind. I allude, of course, to Bichat, whose reputation is steadily increasing as our knowledge advances, and who, if we compare the shortness of his life with the reach and depth of his views, must be pronounced the most profound thinker and the most consummate observer by whom the organization of the animal frame has yet been studied.[1088] He wanted, indeed, that comprehensive knowledge for which Cuvier was remarkable; but though, on this account, his generalizations were drawn from a smaller surface, they were, on the other hand, less provisional: they were, I think, more complete, and certainly they dealt with more momentous topics. For the attention of Bichat was preëminently directed to the human frame[1089] in the largest sense of the word; his object being so to investigate the organization of man, as to rise, if possible, to some knowledge concerning the causes and nature of life. In this magnificent enterprise, considered as a whole, he failed; but what he effected in certain parts of it is so extraordinary, and has given such an impetus to some of the highest branches of inquiry, that I will briefly indicate his method, in order to compare it with that other method which, at the same moment, Cuvier adopted with immense success.
The important step taken by Cuvier was, that he insisted on the necessity of a comprehensive study of the organs of animals, instead of following the old plan of merely describing their habits and external peculiarities. This was a vast improvement, since, in the place of loose and popular observations, he substituted direct experiment, and hence introduced into zoology a precision formerly unknown.[1090] But Bichat, with a still keener insight, saw that even this was not enough. He saw that, each organ being composed of different tissues, it was requisite to study the tissues themselves, before we could learn the way in which, by their combinations, the organs are produced. This, like all really great ideas, was not entirely struck out by a single man; for the physiological value of the tissues had been recognized by three or four of the immediate predecessors of Bichat, such as Carmichael, Smyth, Bonn, Bordeu, and Fallopius. These inquirers, however, notwithstanding their industry, had effected nothing of much moment, since, though they collected several special facts, there was in their observations that want of harmony and that general incompleteness always characteristic of the labours of men who do not rise to a commanding view of the subject with which they deal.[1091]
It was under these circumstances that Bichat began those researches, which, looking at their actual and still more at their prospective results, are probably the most valuable contribution ever made to physiology by a single mind. In 1801, only a year before his death,[1092] he published his great work on anatomy, in which the study of the organs is made altogether subservient to the study of the tissues composing them. He lays it down, that the body of man consists of twenty-one distinct tissues, all of which, though essentially different, have in common the two great properties of extensibility and contractility.[1093] These tissues he, with indefatigable industry,[1094] subjected to every sort of examination; he examined them in different ages and diseases, with a view to ascertain the laws of their normal and pathological development.[1095] He studied the way each tissue is affected by moisture, air, and temperature; also the way in which their properties are altered by various chemical substances,[1096] and even their effect on the taste.[1097] By these means, and by many other experiments tending in the same direction, he took so great and sudden a step, that he is to be regarded not merely as an innovator on an old science, but rather as the creator of a new one.[1098] And although subsequent observers have corrected some of his conclusions, this has only been done by following his method; the value of which is now so generally recognized, that it is adopted by nearly all the best anatomists, who, differing in other points, are agreed as to the necessity of basing the future progress of anatomy on a knowledge of the tissues, the supreme importance of which Bichat was the first to perceive.[1099]
The methods of Bichat and of Cuvier, when put together, exhaust the actual resources of zoological science; so that all subsequent naturalists have been compelled to follow one of these two schemes; that is, either to follow Cuvier in comparing the organs of animals, or else to follow Bichat in comparing the tissues which compose the organs.[1100] And inasmuch as one comparison is chiefly suggestive of function, and the other comparison of structure, it is evident, that to raise the study of the animal world to the highest point of which it is capable, both these great plans are necessary; but if we ask which of the two plans, unaided by the other, is more likely to produce important results, the palm must, I think, be yielded to that proposed by Bichat. Certainly, if we look at the question as one to be decided by authority, a majority of the most eminent anatomists and physiologists now incline to the side of Bichat, rather than to that of Cuvier; while, as a matter of history, it may be proved that the reputation of Bichat has, with the advance of knowledge, increased more rapidly than that of his great rival. What, however, appears to me still more decisive, is, that the two most important discoveries made in our time respecting the classification of animals, are entirely the result of the method which Bichat suggested. The first discovery is that made by Agassiz, who, in the course of his ichthyological researches, was led to perceive that the arrangement by Cuvier according to organs, did not fulfil its purpose in regard to fossil fishes, because in the lapse of ages the characteristics of their structure were destroyed.[1101] He, therefore, adopted the only other remaining plan, and studied the tissues, which, being less complex than the organs, are oftener found intact. The result was the very remarkable discovery, that the tegumentary membrane of fishes is so intimately connected with their organization, that if the whole of a fish has perished except this membrane, it is practicable, by noting its characteristics, to reconstruct the animal in its most essential parts. Of the value of this principle of harmony, some idea may be formed from the circumstance, that on it Agassiz has based the whole of that celebrated classification, of which he is the sole author, and by which fossil ichthyology has for the first time assumed a precise and definite shape.[1102]