organic phenomena which gives them a special place, although the speciality may only be due to a complication of general agencies.

VITAL FORCE.

14. A similar ambiguity to that of the phrase "ordinary matter" lies in the equally common phrase " Vital Force," which is used to designate a special group of agencies, and is then made to designate an agent which has no kinship with the general group; that is to say, instead of being employed in its real signification- that which alone represents our knowledge as the abstract statical expression of the complex conditions necessary to the manifestation of vital phenomena, or as the abstract dynamical expression of the phenomena themselves, it is employed as an expression of their unknown Cause, which, because unknown, is dissociated from the known conditions, and erected into a mysterious Principle, having no kinship with Matter. In the first sense the term is a shorthand symbol of what is known and inferred. The known conditions are the relations of an organism and its medium, the organism being the union of various substances all of which have their peculiar properties when isolated; properties that disappear in the union, and are replaced by others, which result from the combination as the properties of chlorine and sodium all disappear in the sea-salt which results from their union; or as the properties of oxygen and the properties of hydrogen disappear and are replaced by the properties of water. When therefore Vital Force is said to be exalted or depressed, the phrase has rational interpretation in the alteration which has taken place in one or more of the conditions, internal and external: a change in the tissues, the plasma, or the environment, exalts or depresses the energy of the vital manifestations; and to suppose that this is effected

through the agency of some extra-organic Principle is a purely gratuitous fiction.

15. That we are ignorant of one or more of the indispensable conditions symbolized in the abstract term Vitality or Vital Force, is no reason for quitting the secure though difficult path of Observation, and rushing into the facile but delusive path of Fiction, which proposes metempirical Agents (in the shape of Vital and Psychical Principles) to solve the problems of Life and Mind. We may employ the term Vital Force to label our observations, together with all that still remains unobserved; and we are bound to recognize the line which separates observation from inference, what is proved from what is inferred; but while marking the limits of the known, we are not to displace the known in favor of the unknown. It is said that because of our ignorance we must assume these causes of Life and Mind to be unallied with known material causes, and belonging to a different order of existences. This is to convert ignorance into a proof; and not only so, but to allow what we do not know to displace what we do know. The organicist is ready to admit that much has still to be discovered; the vitalist, taking his stand upon this unknown, denies that what has been discovered is really important, and declares that the real agent is wholly unallied to it. How can he know this? He does not know it; he assumes it; and the chief evidence he adduces is that the ordinary laws of inorganic matter are incapable of explaining the phenomena of organized matter; and that physical and chemical forces are controlled by vital force. I accept both these positions, stripping them, however, of their ambiguities. The laws of ordinary matter are clearly incompetent in the case of matter which is not ordinary, but specialized in organisms; and when we come to treat of Materialism we shall see how unscientific have been the hypotheses which disre

gard the distinction. The question of control is too interesting and important to be passed over here.

VITAL FORCE CONTROLLING PHYSICAL AND CHEMICAL FORCES.

16. The facts relied on by the vitalists are facts which every organicist will emphasize, though he will interpret them differently. When, for example, it is said that "Life resists the effect of mechanical friction," and the proof adduced is the fact that the friction which will thin and wear away a dead body is actually the cause of the thickening of a living — the skin of a laborer's hand being thickened by his labor; the explanation is not that Life, an extra-organic agent, "resists mechanical friction" for the mechanical effect is not resisted (the skin is rubbed off the rower's hand sooner than the wood is rubbed off the oar) but that Life, i. e. organic activity repairs the waste of tissue.

17. Again, although many of the physical and chemical processes which invariably take place under the influences to which the substances are subjected out of the organism, will not take place at all, or will take place in different degrees, when the substances are in the organism, this is important as an argument against the notion of vital phenomena being deducible from physical and chemical laws, but is valueless as evidence in favor of an extraorganic agent. Let us glance at one or two striking examples.

18. No experimental inquirer can have failed to observe the often contradictory results which seemingly unimportant variations in the conditions bring about; no one can have failed to observe what are called chemical affinities wholly frustrated by vital conditions. Even the ordinary laws of Diffusion are not always followed in the organism. The Amoeba, though semifluid, resists diffusion when alive; but when it dies it swells and bursts by osmosis. The

exchange of gases does not take place in the tissues, precisely as in our retorts. The living muscle respires, that is, takes up oxygen and gives out carbonic acid, not on the principle of simple diffusion, but by two separable physiological processes. The carbonic acid is given out, even when there is no oxygen whatever present in the atmosphere, and its place may then be supplied by hydrogen; and this physiological process is so different from the physical process which goes on in the dead muscle (the result of putrefaction), that it has been proved by Ranke to go on when the temperature is so low that all putrefaction is arrested. The same experimenter finds * that whereas living nerve will take up, by imbibition, 10 per cent of potash salts, it will not take up 1 per cent of soda salts, presented in equal concentration; and he points to the general fact that the absorption of inorganic substances does not take place according to the simple laws of diffusion, but that living tissues have special laws, the nerve, for instance, having a greater affinity for neutral potash salts than for neutral soda salts. Let me add, by way of anticipating the probable argument that may urge this in favor of Vital Principle which is lightly credited with the prescience of final causes, that so far from this "elective affinity" of the tissues being intelligent and always favorable, Ranke's experiments unequivocally show that it is more active towards destructive, poisonous substances, than towards the reparative, alimentary substances; which is indeed consistent with the familiar experience that poisons are more readily absorbed than foods, when both are brought to the tissues. Thus it is well known. that of all the salts the sulphate of copper is that which plants most readily absorb and it kills them. The special affinities disappear as the vitality disappears, and dying plants absorb all salts equally.

*RANKE, Die Lebensbedingungen der Nerven, 1868, p. 80.

B

*

19. The more the organism is studied, the more evident it will become that the simple laws of diffusion, as presented in anorganisms rarely if ever take effect in tissues; in other words, what is called Imbibition in Physics is the somewhat different process of Absorption in Physiology. The difference is notable in this capital fact, that whereas the physical diffusion of liquids and gases is determined by differences of density, the physiological absorption of liquids and gases is determined by the molecular organization of the tissue, which is perfectly indifferent to, and resists the entrance of, all substances incapable of entering into organic combination, either as aliment or poison. A curious example of the indifference of organized substances to some external influences and their reaction upon others, is the impossibility of provoking ciliary movement in an epithelial cell, during repose, by any electrical, mechanical, or chemical stimuli except potash and soda. Virchow discovered that a minute quantity of either of these, added to the water in which the cell floated, at once called forth the ciliary movements.

20. The true meaning of the resistance of Vitality to ordinary chemical affinity is, that the conditions involved in the phenomena of Vitality are not the conditions involved in the phenomena of Chemistry; in other words, that in the living organism the substances are placed under conditions different from those in which we observe these substances when their chemical affinities are displayed in anorganisms. But we need not go beyond the laboratory to see abundant examples of this so-called resistance to chemical affinity, when the conditions are altered. The decomposition of carbonates by tartaric acid. is a chemical process which is wholly resisted if alcohol

* "Il n'y a peut être pas un seul phénomène chimique dans l'organisme qui se fasse par les procédés de la chimie de laboratoire; en particulier il n'y a peut être pas une oxydation qui s'accomplisse par fixation directe d'oxygène."-CLAUDE BERNARD.