ject them to pathological procedures, regarding such exceptions as true maladies, of a deeper and more obscure origin than others, and of a more incurable nature;-considerations which, of course, reduce their scientific value. This resource shares with pathology the advantage of being applicable through the whole range of the biological system.

It is still necessary to insist that, in either method of experimentation, direct or indirect, artificial or natural, the elementary rules should be kept in view; first, to have a determinate aim; that is, to seek to illustrate an organic phenomenon, under a special aspect; and, secondly, to understand beforehand the normal state, and its limits of variation. In regard to the more advanced sciences, it would seem puerile to recommend such maxims as these; but we must still insist on them in biology. It is through neglect of them that all the observations yet collected on the derangements of the intellectual and moral phenomena have yielded scarcely any knowledge of their laws. Thus, whatever may be the value of the most suitable method of experimentation, we must ever remember that here, as elsewhere, and more than elsewhere, pure observation must always hold the first rank, as casting light, primarily, on the whole subject, which it is proposed to examine afterwards, as a special study, with a determinate view, by the method of experimentation.

In the third place, we have to review the

COMPARISON. method of Comparison, which is so specially adapted to the study of living bodies, and by which, above all others, that study must be advanced. In Astronomy, this method is necessarily inapplicable: and it is not till we arrive at Chemistry that this third means of investigation can be used; and then, only in subordination to the two others. It is in the study, both statical and dynamical, of living bodies, that it first acquires its full development; and its use elsewhere can be only through its application

here.

The fundamental condition of its use is the unity of the principal subject, in combination with a great diversity of actual modifications. According to the definition of life, this combination is eminently realized in the study of

biological phenomena, however regarded. The whole system of biological science is derived, as we have seen, from one great philosophical conception; the necessary correspondence between the ideas of organization and those of life. There cannot be a more perfect fundamental unity of subject than this; and it is unnecessary to insist upon the almost indefinite variety of its modifications,-statical and dynamical. In a purely anatomical view, all possible organisms, all the parts of each organism, and all the different states of each, necessarily present a common basis of structure and of composition, whence proceed successively the different secondary organizations which constitute tissues, organs, and systems of organs, more or less complicated. In the same way, in a physiological view, all living beings, from vegetable to man, considered in all the acts and periods of their existence, are endowed with a certain common vitality, which is a necessary basis of the innumerable phenomena which characterize them in their degrees. Both these aspects present as most important, and really fundamental, what there is in common among all the cases; and their particularities as of less consequence; which is in accordance with the great prevalent law, that the more general phenomena overrule the less. Thus broad and sound is the basis of the comparative method, in regard to biology.

At the first glance the immensity of the science is overwhelming to the understanding, embracing as it does all organic and vital cases, which it appears impossible ever to reduce within the compass of our knowledge: and no doubt, the discouragement hence arising is one cause of the backwardness of biological philosophy. Yet the truth is that this very magnitude affords, not an obstacle, but a facility to the perfecting of the science, by means of the luminous comparison which results from it, when once the human mind becomes familiar enough with the conditions of the study to dispose its materials so as to illustrate each other. The science could make no real progress while Man was studied as an isolated subject. Man must necessarily be the type; because he is the most complete epitome of the whole range of cases: Man, in his adult and normal state, is the representative of the great scientific unity, whence

the successive terms of the great biological series recede, till they terminate in the simplest organizations, and the most imperfect modes of existence. But the science would remain in the most defective state in regard to Man himself, if it were not pursued through a perpetual comparison, under all possible aspects, of the first term with all inferior ones, till the simplest was reached: and then, back again, through the successive complications which occur between the lowest type and the highest. This is the most general, the most certain, the most effectual method of studying physiological as well as anatomical phenomena. Not only is there thus a greater number of cases known, but each case is much better understood by their approximation. This would not be the case, and the problem would be embarrassed instead of simplified, if there were not a fundamental resemblance among the whole series, accompanied by gradual modifications, always regulated in their course: and this is the reason why the comparative method is appropriate to biology alone, of all the sciences, except, as we shall see hereafter, in social physics.

Complete and spontaneous as this harmony really is, no philosopher can contemplate without admiration the eminent art by which the human mind has been aided to convert into a potent means what appeared at first to be a formidable difficulty. I know no stronger evidence of the force of human reason than such a transformation affords. And in this case, as in every other in which primordial scientific powers are concerned, it is the work of the whole race, gradually developed in the course of ages, and not the original product of any isolated mind, however some moderns may be asserted to be the creators of comparative biology. Between the primitive use that Aristotle made of this method in the easiest cases,-as in comparing the structure of Man's upper and lower limbs,-to the most profound and abstract approximations of existing biology, we find a very extensive series of intermediate states, constantly progressive, among which history can point out individually only labours which prove what had been the advance in the spirit of the comparative art at the corresponding period, as manifested by its larger and more effectual application. It is evident that the comparative

KINDS OF COMPARISON.

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method of biologists was no more the invention of an individual than the experimental method of the physicists.

There are five principal heads under which Five kinds of biological comparisons are to be classed. comparison.

1. Comparison between the different parts of the same organism.

2. Comparison between the sexes.

3. Comparison between the various phases presented by the whole of the development.

4. Comparison between the different races or varieties of each species.

5. Lastly, and pre-eminently, Comparison between all the organisms of the biological hierarchy.

It must be understood that the organism is always to be supposed in a normal state. When the laws of that state are fully established, we may pass on to pathological comparison, which will extend the scope of those laws: but we are not yet advanced enough in our knowledge of normal conditions to undertake anything beyond. Moreover, though comparative pathology would be a necessary application of biological science, it cannot form a part of that science, but rather belongs to the future medical science, of which it must form the basis.-Again, biological comparison can take place only between the organisms, and not between them and their medium. When such comparison comes to be instituted, it will be, not as biological science, but as a matter of natural history.

The spirit of biological comparison is the same under all forms. It consists in regarding all cases as radically analogous in respect to the proposed investigation, and in representing their differences as simple modifications of an abstract type; so that secondary differences may be connected with the primary according to uniform laws; these laws constituting the biological philosophy by which each determinate case is to be explained. If the question is anatomical, Man, in his adult and normal state, is taken for the fundamental unity, and all other organizations as successive simplifications, descending from the primitive type, whose essential features will be found in the remotest cases, stripped of all complication. If the question is physiological, we seek the fundamental identity of the chief

phenomenon which characterises the function proposed, amidst the graduated modifications of the series of comparative cases, till we find it isolated, or nearly so, in the simplest case of all; and thence we may trace it back again, clothed in successive complications of secondary qualities. Thus, the theory of analogous existences, which has been offered as a recent innovation, is only the necessary principle of the comparative method, under a new name. It is evident that this method must be of surpassing value when philosophically applied: and also that, delicate as it is, and requiring extreme discrimination and care in its estimate and use, it may be easily converted into a hindrance and embarrassment, by giving occasion to vicious speculations on analogies which are only apparent.

Of the five classes specified above, three only are so marked as to require a notice here: the comparison between the different parts of the same organism; between the different phases of each development; and between the distinct terms of the great hierarchy of living bodies.

Comparison of parts of the same organism.

The method of comparison began with the first of these. Looking no further than Man, no philosophical mind can help being struck by the remarkable resemblance that his different chief parts bear to each other in many respects, both as to structure and function. First, all the tissues, all the apparatus, in as far as they are organized and living, offer those fundamental characteristics which are inherent in the very ideas of organization and life, and to which the lowest organisms are reduced. But, in a more special view, the analogy of the organs becomes more and more marked as that of the functions is so; and the converse; and this often leads to luminous comparisons, anatomical and physiological, passing from the one to the other, alternately. This original and simple method of comparison is by no means driven out by newer processes. It was thus, for instance, that Bichat, whose subject was Man only, and adult Man, discovered the fundamental analogy between the mucous and the cutaneous systems, which has yielded so much advantage to both biology and pathology. And again, with all M. de Blainville's mastery of the principle of the comparative method, we cannot doubt the sufficiency