Scope And Method Of Biology
( Originally Published 1913 )
IT will now be possible to venture on a definition of the Science of Life, and a circumscription of its scope and Method. We have seen that the idea of Life pre-supposes the constant correlation of two indispensable elements, an organism and a medium (understanding by medium the whole of the surrounding circumstances necessary to the existence of the organism). From the reciprocal action of these two elements result all the phenomena of life. Hence it follows that the great problem of Biology is to establish for every case, by the smallest possible number of invariable laws, an exact harmony between these two inseparable powers—the vital conflict and the act which constitutes it; in other words, to connect the twofold idea of organ and medium with that of function. Thus, positive Biology is destined to connect, in every determinate case, the anatomical with the physiological point of view, the static with the dynamic condition. It is this which constitutes its true philosophic character. Placed in a given set of circumstances, every organism must always act in a determinate manner; and inversely, the same action cannot be identically produced by organisms really distinct. So that we may infer the agent from the act, or the act from the agent. The medium being presupposed as thoroughly known, in consequence of the results attained by the Preliminary Sciences, the twofold biological problem may thus receive its formula :
Given the organ or the organic modification, to find the function or the act, and reciprocally.
That Biology is far from a state of positivism to admit of such scientific prevision, except in minor cases, no person familiar with the science need be told. This was still more the case at the time Comte published his views, viz. in 1838. And although in the first volume of his Politique Positive, published in 1851, he alludes to - the important discoveries of Schwann, relative to the " cell doctrine," it is plain that he has not followed with much attention the rapid course of physiological investigation. I mention this for the sake of those who are about to study his work. Not that the present state of the science in any way modifies the general philosophic considerations he has set forth with such profound and exhaustive insight. What Buffon said of Pliny may be truly applied to Comte : he has cette facilité de penser en grand qui multiplie la science—" that capacity for large generalizations which enriches science."
The definition of the science given, let us now examine its Method. The philosophic law, laid down by Comte, respecting the augmentation of our scientific resources according as the phenomena become more complicated, receives in Biology an unequivocal illustration. If the phenomena of life are incomparably more complex than those of the inorganic world, our means of exploring them are also more extensive. He has already pointed out the three capital arts of exploration, viz., Observation, Experiment, and Comparison and he proceeds to show at great length how these three arts are employed in Biology.
Of Observation, properly so called, we not only find a great extension in the study of life, resulting from the countless variety of phenomena to be observed, but also from the employment of artificial means whereby our senses are raised to an incalculably higher power : such, for example, as the microscope and stethoscope. No one even superficially acquainted with microscopical researches will fail to see their immense importance, in spite of the errors into which the very difficulty of rightly observing, and the tendency to see what they wish to see, have led inquirers. What would our know-ledge of the tissues be without the microscope ?
Of Experiment, in the strict sense of the word as used in Physics and Chemistry, there can be but little employment : the complexity and connexity (if I may coin the word) of the phenomena prevent that indispensable elimination of all the circumstances except the one which we desire to observe ; and almost all direct experiments are rendered equivocal by the impossibility of isolating the phenomena. Yet Biology has a kind of experiment peculiar to itself, and rich in indications, viz., the experiments Nature herself makes for us in the various anomalies of organization, and the various abnormal indications which we denominate Disease.
Comparison is, however, the great art of Biology, and Comte is right in devoting to it the great space he does. Instinctively men avail themselves of this fertile source of knowledge ; but so little philosophic conviction is there of its paramount importance, that not one physiologist in a hundred conceives himself to be violating scientific Method in beginning and ending his studies with the physiology of man ! To begin the study of Euclid at the twelfth book would not be more absurd. Our ascent must be gradual. Taking a broad survey of all its manifestations, we find that Life has two grand divisions —Vegetative and Animal; or, to use Bichat's language, Organic Life and Relative Life. We see Plants and Animals, the latter feeding on the former; but we also see that the Animal itself is only distinguished from the Plant by the possession of certain faculties over and above those of Organic or Vegetative life—viz., the faculties of sensation and locomotion. Equally to the Animal as to the Plant are organs of nutrition and re-production indispensable; and Cuvier's notion of an animal being able to live for a moment by its Animal Life alone, betrays a profound misconception of the nature of Life. As it is the vegetables which supply Animals with food, so in Animals it is the vegetative life which supports the relative life.
Physiologists have not sufficiently borne in mind that although in Man the Animal Life has a predominance over the Vegetative Life, nevertheless it is only superposed on the Vegetative, and can never for an instant be independent of it. Nature presents to us a marvellous procession from the Plant, which has only Organic Life, to the Zoophyte, which exhibits a commencement of Animal Life, up through Animals to Man, with a gradual complexity of organism, and gradual enhance-ment of the animal life ; so that from simple processes of assimilation and reproduction our investigation rises to locomotion, sensation, intelligence, morality, and sociality ! The great dynamic difference between in-organic and organic—that is to say, the first vital act, is assimilation; add thereto the act of reproduction, and you have the whole life of a cell, the simplest of organisms.
"A cell," says Dr. Carpenter, in physiological language is a closed vesicle, or minute bag, formed by a membrane in which no definite structure can be discerned, and having a cavity which may contain matter of variable consistence. Every such cell constitutes an entire organism in such simple plants as red snow or gory dew ; for although the patches of this kind of vegetation which attract notice are made up of vast aggregations of such cells, yet they have no dependence upon one another, and the actions of each are an exact repetition of those of the rest." The cell, in short, is a plant—minute, yet individual—and its powers of reproduction (i. e., of throwing off cells similar to itself,) is so great, that extensive tracts of snow are reddened quite suddenly by the Protococcus nivalis (red snow.) " In such a cell," continues Dr. Carpenter, " every organized fabric, however complex, originates. The vast tree, almost a forest in itself—the zoophyte, in which we discover the lowest indications of animality—and the feeling, thinking, intelligent man—each springs from a germ that differs in no obvious particular from the permanent condition of one of those lowly beings."
Although we use the phrase " Vegetative Life," we must, as Valentin says, guard against the popular error of supposing that the animal and vegetable kingdoms correspond in all particulars ; " that there is a digestion, a respiration, a perspiration, and an excretion in plants as well as animals. A more accurate examination teaches that this is not the case. Vegetables possess no tissues which allow of the same kind of nutritive absorption, of distribution of juices, or of secretion, that we meet with in at least the higher animals. They have no large cavities in which considerable quantities of food can be collected, and dissolved by special fluid secretions. They possess no point midway in the movement of their juices, and no mechanism other than that of a casual and secondary apparatus for the inhaustion or expulsion of the respiratory gases. They are devoid of the changeable epithelial coverings which play an important part in many of the animal excretory organs. In one word, the general organic functions are introduced into the two living kingdoms of nature, and probably even into their subordinate divisions, by two different ways. This difference leads at once to the conclusion, that the structure of the animal is not a simple repetition of that of the plant; with the addition of a series of new apparatus. The nature of the tissues, the mode of their action and change, the form, division, and destiny of the organs,—all these rather teach us that animals of any development are constructed upon an altogether different plan."
I point to this identity of the biological series, and to the necessity of the processional method of studying the series, for the sake of making more apparent the indispensable method of comparison. Only by studying the varieties of the organism, as manifested in its increasing complexity of structure and intensity of power, can we rightly appreciate it. Cuvier well says, that the examination of the comparative anatomy of an organ, in its ascending gradation from the simplest to the most complex state (or, as he and the majority of the French writers prefer to study it, in the descending degradation, from the most complex to the most simple,) is equivalent to an experiment which consists in removing successive portions of the organ with a view to ascertain its essential part. Take, for example, the ear. The essential part is unquestionably the vestibule ; all the other portions, the semicircular canals, the cochlea, the tympanum and its contents, are successive additions corresponding with the increasing perceptive powers.
Comparative Anatomy is therefore the basis of Philosophical Anatomy, and before we can understand the Laws of Life it is indispensable that we embrace the whole variety of vital phenomena : a stupendous task, and one which, with Comte, we may justly regard as one of the greatest testimonies to the power 6f man's intellect.
It is requisite, says Comte, to distinguish the diverse aspects in which biological comparison may be viewed. First, Comparison between the various parts of each organism; Second, Between the sexes; Third, Between the diverse phases presented in the ensemble of development; Fourth, Between the races or varieties of each species ; Fifth, Between all the organisms of the hierarchy.
Every one who has made any extensive biological research will have felt the necessity for a constant recurrence to the comparative method ; and I would point also to the equally fundamental law of assimilation as an appreciable illustration. Seeing that the first example of transformation of inorganic into organic matter takes place in vegetable assimilation, and that all the subsequent transformations into higher tissues are but modifications of that one process, it is clear that the elementary laws of assimilation may more easily be detected in the vegetable than in the animal world.