Part 15

20. Three Lectures on Experimental Embryology. Oxford, 1917.

VITALISM

By J. W. Jenkinson

In one of the oldest biological treatises in the world, the soul or life of an organism is defined in the most general way as an activity of a natural organic living body--ἐντελέχεια σώματος φυσικου̑ ὀργανικου̑ δυνάμει ζωὴν ἔχοντος--life being autonomous nutrition and growth and decay. The activity may, however, be latent or patent, passive or active, sleeping or waking, without losing its peculiar characters. It is substance (οὐσία), but substance as ‘form’ as opposed to the material substance of the body, and the living body is therefore also a substance in a double sense.

It is not identical with the body; but as form, proportion (λόγος), activity (ἐνέργεια), essence (τὸ τί ἠν εἰναι), it is related to the body, mere matter (ὕλη), and potentiality (δύναμις) in just the same way as the seal is related to the wax; and the body is the instrument whereby it effects its purposes; though subsequent in time, it is prior in thought to the body, as all activities are to the materials with which they operate.

At the same time neither it nor its parts are separable from the body, with the exception, possibly, of mind (νου̑ς); it is indeed the actual or possible functioning of the body, like the seeing of the eye or the cutting of the axe, and with the disappearance of the capacity of this functioning the soul itself also perishes. Lastly, it is a cause (ἀρχὴ καὶ αἰτία) in a triple sense: first, as the source of motion; secondly, as that for the sake of which the body exists; and thirdly, as its essence (οὐσία) or formal cause. The soul or life is of several kinds, which form together an ascending series each member of which is necessarily involved in those above it.

The lowest is the nutritive soul (θρεπτική), found in all living things, and the only soul possessed by plants. It is defined as motion in respect of nutrition, decay, and growth, processes which involve alteration (ἀλλοίωσις) in the body; and its functions (ἔργα) are to utilize food for the maintenance and reproduction of the form of the body, and to control and limit growth.

The second is the perceptive soul (αἰσθητική), the possession of which distinguishes animals from plants. This also is a kind of alteration (ἀλλοίωσις τίς) and consists in being moved and affected. The fundamental and indispensable perception is touch (ἁφή), for it is concerned in the acquisition of the food. It is invariably present: the others may or may not, some or all, coexist with it.

Thirdly, some animals are possessed of a capacity for locomotion, and the performance of this function requires again a special kind of soul.

Lastly, there is the reasoning soul (διανοητικά) or mind (νου̑ς). This is found in man alone, unless there be other beings similar to him, or even nobler than he. Mind alone is eternal and separable from the body.

Though the observation and experiment of modern science would doubtless find much to alter in the details of these simple definitions, yet it must be conceded that, by what is certainly a most fortunate guess if it is not the most wonderful insight, Aristotle has laid his finger on the cardinal point of modern physiological doctrine. For, putting aside for the moment the mental faculties, it is here laid down in the clearest manner that not only the functions of growth and decay, nutrition, and reproduction, but also the capacity of responding to stimuli are to be ultimately resolved into some kind of movement of the particles of which the body is composed. Life, in short, as we might say with Virchow, is a mode of motion.

The biology of to-day distinguishes living from inanimate bodies by the possession and exercise of the three principal properties or functions of metabolism, irritability, and reproduction; and further, the body which performs these functions is not only composed of chemically complex substances--proteids--which are not found in things that are not alive, but possesses a structure. In no case, even the simplest, is the organism a mere homogeneous lump of protoplasm, but it has parts or organs, visibly different from one another, and obviously correlated with the activities appropriated to each; and it is the preservation of that structure, in the individual and in the race, which is the end towards which the collective performance of all these functions, or the life of the organism, is apparently directed.

Some of these peculiarities are shared by certain things that are not commonly regarded as alive. Crystals have of course a definite structure; they can divide, and when broken they can make good the missing part, but they do not assimilate to the substance of their own bodies a food-material which is less complex than it, and they are not irritable.

The differences, indeed, between the living and the lifeless are so profound, that it is not to be wondered at that there should have been in all ages natural philosophers who have held that living activities are phenomena sui generis, differing toto caelo from the properties exhibited by lifeless bodies, and never by any conceivability to be expressed in terms of these.

This doctrine is vitalism.

It exists in several varieties, but one at least is of very ancient lineage and can be traced back through mediaeval times to the biological speculations of the Greeks.

Whether Aristotle really held the vitalistic views which have since been attributed to him is a matter we shall have to discuss later on, but it is certain that in the writings of Galen there is to be found a theory of life which bears the stamp of Aristotelian influence, and was destined to hand that influence on to future generations. Galen admits the sensitive soul of Aristotle as the peculiarity of animals, and the rational soul for man, but substitutes for the nutritive soul certain works of nature--attraction, repulsion, retention, alteration. And further, the rational soul is no longer immortal, but perishable, and is dependent on the body, where its seat is in the brain; it is material or quasi-material, a πνευμα, most efficient when dry.

After a long interval this doctrine reappears in the sixteenth century in the writings of Vesalius, who tells us that the heart has a vital soul, the liver a natural soul, while there is elaborated in the ventricles of the brain an animal spirit or principal soul.

Meanwhile, however, the conception of life as something material had been discarded by Paracelsus for the belief that the soul, or as he called it, the ‘Archaeus’, by which the chemical processes of the body are governed, is not a material but a spiritual force, a view restated by Stahl more than a hundred years afterwards. ‘The events of the body’, says this author, ‘may be rough-hewn by chemical and physical forces, but the soul will shape them to its own ends, and will do that by its instrument, motion.’

This, of course, is vitalism, and vitalism in its extreme or ‘animistic’ form. The idea recurs later on in the biology of Treviranus. To be living is to have a soul, he tells us, and the conscious Lebenskraft employs the forces of the material world to form the organism. ‘Das Weitzenkorn hat allerdings Bewusstsein dessen, was in ihm ist und aus ihm werden kann, und träumt wirklich davon.’ Though he adds quaintly enough, ‘Sein Bewusstsein und seine Träume mögen dunkel genug sein’. It is curious to observe the revival, at the beginning of the twentieth century, of this mediaeval mysticism in the speculative writings of so accomplished an experimentalist as Hans Driesch.

Driesch is an embryologist who in his earlier days had enunciated an invaluable analytical theory of development, a theory which suggests that while the formation of the first or elementary organs that appear in the embryo or larva--such structures as the larval gut or sense-organ, or the germ-layers--depends upon the presence in the germ of certain specific organ-forming substances (and this is a fact which has since been abundantly demonstrated by experiment), the origin of parts that appear later in development may be accounted for by the action of the first-formed structures upon one another, these actions being in the nature of physiological responses to stimuli; and for this also some evidence has been produced. On this view differentiation is a mechanical process, set in motion by fertilization or some other cause, and, given a certain initial structure of the germ or ovum, given the presence in it of a certain number of parts or substances capable of acting upon one another with a fixed co-ordination or harmony of the stimuli and the responses, given further a proper constitution of the external environment, then a definite result must follow, the production of an organism which is like the parents that gave it birth.

But in his later treatises this hypothesis has been repudiated, and, by a remarkable volte-face, replaced by a dogma of a wholly different kind. For now it is urged that no merely material factors can possibly account either for the harmony of development--the due co-ordination of mutually reacting parts; or for the secondary harmony of composition--the formation of complex organs by the union of tissues; or for the functional harmony seen in the activities of the adult.

For example, it is asserted that any fragment of an egg of a sea-urchin, if not too small (not less than 1/32 of the egg), can give rise to a whole and normal larva. We are told that the cells of the segmented ovum may be disarranged to any extent by various means, such as raising the temperature, diluting the sea-water, removing the calcium from the sea-water, or by shaking, without prejudice to the ultimate normality of development. Each part of the ovum can therefore, according to the needs of the case, give rise to any part of the resulting organism. ‘Jeder Teil kann nach Bedürfniss jedes.’

And thirdly, when the gastrula of a sea-urchin is transversely divided into two, each half, it is stated, develops into a diminished whole larva in which the gut becomes divided into the characteristic three regions, and all the other organs are formed in correct proportion.

For each of these acts of development in the whole uninjured larva an explanation may conceivably be given in terms of formative stimuli exerted by the originally distinct parts of the egg and calling forth responses in other parts. A mechanism may be thought of which, when set in motion, will achieve a certain end in accordance with its own pre-established harmony; but a mechanism which can be subdivided ad libitum, or almost ad libitum, and the parts of which will still achieve the same end, will still behave as wholes with their parts co-ordinated in the same ratio, temporally and spatially! Such a mechanism is inconceivable; for to ensure the uniform result, the relative amounts and positions of the necessary substances must be imagined as identical in every possible fragment of the egg that is not too small. Something is therefore required to superintend, to co-ordinate the causes of development in the case not only of the part but of the whole egg as well; and this something is not material. A corroborative proof of the inadequacy of the purely material explanation--the causal explanation in the ordinary sense of the phrase--may be derived from a consideration of certain other vital processes. The facts of acclimatization and immunity betray an extraordinary adaptability of the organism to a change in its environment; an organ will adapt itself structurally to an alteration, quantitative or qualitative, of function [Roux’s ‘Functional Adaptation’]; lost parts can be regenerated; and then there is the physiology of the nervous system.

In all these cases of ‘regulation’--and indeed in all other responses to stimuli--the same element, inexplicable in chemical and physical terms, exists and must exist in development. This entity is not a form of energy, but a vital constant, analogous to the constants or ultimate conceptions of mechanics and physics and chemistry and crystallography, but not reducible to these, just as these cannot be translated into one another.

Driesch describes it as a rudimentary feeling and willing, a ‘psychoid’, ‘morphaesthetic’ or perceptive of that form which is the desired end towards which it controls and directs all the material elements of differentiation, like the grain of wheat of Treviranus, dreaming dimly of its destiny. It is thus a vera causa--an unconditional and invariable antecedent--a psychical factor which can intervene in the purely physical series of causes and effects, and for it he revives the Aristotelian term ‘Entelechy’.

Such is the ‘vitalism’ introduced by Hans Driesch, a teleological theory clearly, but no mere metaphysical doctrine of final causes: rather a dynamic teleology which not only sees an end in every organic process, but postulates an immaterial entity to guide the merely mechanical forces towards the realization of that end.