MEANS OF INVESTIGATION.

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Chemical exploration.

a sort of new power, to perfect the preliminary exploration of the subject of his researches, according to the evident rule of philosophy that each doctrine may be converted into a method with regard to those that follow it in the scientific hierarchy; but never with regard to those which precede it. In anatomical observations, especially, as might be foreseen, a happy use is made of chemical procedure, to characterize with precision the different elementary tissues, and the chief products of the organism. In physiological observations also, though they are less favourable to the use of such means, they are of real and notable efficacy,-always supposing, in both cases, that they are used under the guidance of sound philosophy, and not overcharged with the minute numerical details which too often burden the chemical analyses of the organic tissues. One more resource may be mentioned, which was often employed by Bichat to make up for the absence or imperfection of chemical tests; the examination of alimentary effects, the substances which immediately compose organized bodies being, usually, by their nature, more or less fit for nutrition. In an anatomical view this study may become a useful complement of the other means of investigation.

EXPERIMENT.

Proceeding to the second class of means,Experiment cannot but be less and less decisive, in proportion to the complexity of the phenomena to be explored: and therefore we saw this resource to be less effectual in chemistry than in physics; and we now find that it is eminently useful in chemistry in comparison with physiology. In fact, the nature of the phenomena seems to offer almost insurmountable impediments to any extensive and prolific application of such a procedure in biology. These phenomena require the concurrence of so large a number of distinct influences, external and internal, which, however diverse, are closely connected with each other, and yet within narrow limits, that, however easy it may be to disturb or suspend the process under notice, it is beyond measure difficult to effect a determinate perturbation. If too powerful, it would obviate the phenomenon: if too feeble, it would not sufficiently mark the artificial case. And, on the other hand, though intended

and directed to modify one only of the phenomena, it must presently affect several others, in virtue of their mutual sympathy. Thus, it requires a highly philosophical spirit, acting with extreme circumspection, to conduct physiological experiments at all; and it is no wonder if such experiments have, with a few happy exceptions, raised scientific difficulties greater than those proposed to be solved, to say nothing of those innumerable experiments which, having no definite aim, have merely encumbered the science with idle and unconnected details.

By affecting the organism.

In accordance with what has been said of the mutual relations of the organism and its environment, we must bear in mind that experiments in physiology must be of two kinds. We must introduce determinate perturbations into the medium as well as the organism; whereas the latter process has alone been commonly attempted. If it is objected that the organism must itself be disturbed by such affection of the medium, the answer is that the study of this reaction is itself a part of the experiment. It should be remarked that experimentation on the organism is much the less rational of the two methods, because the conditions of experiment are much less easily fulfilled. The first rule, that the change introduced shall be fully compatible with the existence of the phenomenon to be observed, is rendered often impracticable by the incompatibility of life with much alteration of the organs: and the second rule,―that the two compared cases shall differ under only one point of view,—is baffled by the mutual sympathy of the organs, which is very different from their harmony with their environment. In both lights, nothing can be imagined more futile in the way of experiment than the practice of vivisection, which is the commonest of all. Setting aside the consideration of the cruelty, the levity, and the bad moral stimulus involved in the case, it must be pronounced absurd; for any positive solution is rendered impossible by the induced death of a system eminently indivisible, and the universal disturbance of the organism under its approach.

By affecting The second class of physiological experithe Medium. ments appears to me much more promising;

-that in which the system of exterior circumstances is modified for a determinate purpose. Scarcely anything has been done in this direction beyond some incomplete researches into the action of artificial atmospheres, and the comparative influence of different kinds of alimentation. We are here better able to circumscribe, with scientific precision, the artificial perturbation we produce; we can control the action upon the organism, so that the general disturbance of the system may affect the observation very slightly; and we can suspend the process at pleasure, so as to allow the restoration of the normal state before the organism has undergone any irreparable change. It is easy to see how favourable, in comparison, these conditions are to rational induction. And to these considerations may be added the one more, that under this method we can observe varying states in one individual; whereas, under the practice of vivisection, we have to observe the normal state in one individual, and the artificial in another. Thus we are justified in our satisfaction that the least violent method of experimentation is the most instructive. As to the application of experiment in the various degrees of the biological scale;-it is easiest in the lower order of organisms, because their organs are simpler and fewer, their mutual sympathy is less, and their environment is more definite and less complex; and these advantages, in my opinion, more than compensate for the restriction of the field of experiment. It is true, we are remote from the human type, which is the fundamental unity of biology; and our judgment is thus impaired, especially with regard to the phenomena of animal life: but, on the other hand, we are all the nearer to the scientific constitution proper to inorganic physics, which I consider to be the ultimate destination of the art of experiment. The advantages at the other end of the scale are that the higher the organism, the more is it susceptible of modification, both from its own complexity and from the greater variety of external influences involved;-every advantage bringing with it, as we have seen, an increase of difficulty.

Comparative experiment.

No one will suppose, I trust, that from anything I have said I have the slightest desire to undervalue the use of

experiment in biology, or to slight such achievements as Harvey's experiments on circulation; Haller's on irritability; part of Spallanzani's on digestion and generation; Bichat's on the triple harmony between the heart, the brain, and the lungs in the superior animals; those of Legallois on animal heat; and many analogous efforts which, seeing the vast difficulty of the subject, may rival the most perfect investigations in physics. My object is simply to rectify the false or exaggerated notions of the capacity of the experimental method, misled by its apparent facility to suppose it the best method of physiological research; which it is not. One consideration remains in this connection; the consideration of the high scientific destination of pathological investigation, regarded as offering, in biology, the real equivalent of experimentation, properly so called. Pathological Investigation.

Precisely in the case in which artificial experimentation is the most difficult, nature fulfils the conditions for us; and it would surely be mistaking the means for the end to insist on introducing into the organism perturbations of our own devising, when we may find them taking place without that additional confusion which is caused by the use of artificial methods. Physiological phenomena lend themselves remarkably to that spontaneous experimentation which results from a comparison of the normal and abnormal states of the organism. The state of disease is not a radically different condition from that of health. The pathological condition is to the physiological simply a prolongation of the limits of variation, higher or lower, proper to each phenomenon of the normal organism; and it can never produce any entirely new phenomenon. Therefore, the accurate idea of the physiological state is the indispensable ground of any sound pathological theory; and therefore, again, must the scientific study of pathological phenomenon be the best way to perfect our investigations into the normal state. The gradual invasion of a malady, and the slow passage from an almost natural condition to one of fully marked disease, are far from being useless preliminaries, got rid of by the abrupt introduction of what may be called the violent malady of direct experi

PATHOLOGICAL INVESTIGATION.

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ment: they offer, on the contrary, inestimable materials to the biologist able to put them to use. And so it is also

in the happy converse case, of the return, spontaneous or contrived, to health, which presents a sort of verification of the primitive analysis. Moreover, the direct examination of the chief phenomenon is not obscured, but much elucidated, by this natural process. And again, it may be applied directly to Man himself, without prejudice to the pathology of animals, and even of vegetables. We may enjoy our power of turning our disasters to the profit of our race and we cannot but deplore the misfortune that our great medical establishments are so constituted as that little rational instruction is obtained from them, for want of complete observations and duly prepared observers.

Here, as elsewhere, the distinction holds of the phenomena belonging to the organism or to the medium; and here, as before, we find the maladies produced from without the most accessible to inquiry. Pathological inquiry is also more suitable than experimental, to the whole biological series; and thus it answers well to extend our observations through the entire hierarchy, though our object may be the study of Man; for his maladies may receive much light from a sound analysis of the derangements of other organisms,-even the vegetable, as we shall see when we treat of the comparative process.

Again, pathological analysis is applicable, not only to all organisms, but to all phenomena of the same organism; whereas direct experimentation is too disturbing and too abrupt to be ever applied with success to certain phenomena which require the most delicate harmony of a varied system of conditions. For instance, the observation of the numerous maladies of the nervous system offers us a special and inestimable means of improving our knowledge of the laws of intellectual and moral phenomena, imperfect as are yet our qualifications for using them. There remains one other means of knowledge under this head; the examination of exceptional organizations, or cases of monstrosity. As might be anticipated, these organic anomalies were the last to pass over from the gaze of a barren curiosity to the investigation of science; but we are now learning to refer them to the laws of the regular organism, and to sub