is approaching extinction. This conclusion is based upon the fact that while every form of energy can be completely converted into heat, heat cannot be completely converted into other forms of energy, nor these into each other. Hence it arises that energy is being gradually dissipated as heat. Moreover, since transformation can only result when heat passes from a higher to a lower temperature, it follows that when that perfect equilibrium of temperature is reached toward which events are tending, there can be no other energy than heat; and this absolutely inconvertible, irrecoverable. To apply this law to the present case, the muscle, for example, is a machine for transforming the energy of food into work. Since, consequently, this conversion is not complete, it follows that heat must appear as a necessary result of muscular action. The heat of animal life, consequently, is not heat especially provided; it is simply the heat which inevitably results from an incomplete conversion of energy.

Again, the form of chemical action generally assumed by physiologists to account for the energy of the living animal has been chemical union, oxidation.67 But the science of thermo-chemistry, as developed in late years by Berthelot and Thomsen,68 has proved that direct union of chemical substances may not only not evolve heat, but may actually absorb it. It appears, too, that thermal changes accompany all forms of chemical change, those of decomposition and exchange as well as those of synthesis. The animal absorbs highly complex substances as food, capable of innumerable stages of retrogressive metamorphosis before elimination. In each of these stages energy may be evolved, this energy being that successively stored up by the plant when these changes were repeated in the inverse order.

Another point of interest has reference to the modern views of capillarity. In 1834, J. W. Draper showed that capillarity is an electrical phenomenon.69 Quite recently, Lippmann has developed and extended this view and fully confirmed it.70 Whenever the free surface of a liquid, curved by capillary action, is electrified it changes its form; and conversely, when such a surface is made by mechanical means to change its form, an electromotive force is developed. Based upon this principle Lippmann constructed a capillary reversible engine and an extremely sensitive capillary electrometer. The former, when a current of electricity was applied to it, developed mechanical work and ran as a motor.

When turned by hand, it became an electromotor. In the animal organism there are it is true but a few free surfaces where this action can take place. But Gore has shown that the same phenomenon appears between two liquids in contact, their boundary being altered in character by electrification.71 Indeed, when we consider the production of electricity by osmose, and of heat and electricity both, by imbibition, both capillary phenomena,72 the wonder is not that so much electrical energy is evolved by the organism, but that it is so little. If the physical and chemical changes which take place within the body took place without it, there would be an abundant evolution of energy. Can we doubt that these changes are the cause of the energy exhibited by the organism?

. Thus far, when we have spoken of a living being, we have had reference to the organism as a whole, and this of a rather complex kind. In this view of the case, however, we find that biological microscopists do not agree with us. "The cell alone," says Küss, "is the essentially vital element."73 Says Beale,-“There is in living matter nothing which can be called a mechanism, nothing in which structure can be discerned. A little transparent colorless material is the seat of these marvellous powers or properties by which the form, structure and function of the tissues and organs of all living things are determined."74 And again, "However much organisms and their tissues in their fully formed state may vary as regards the character, properties and composition of the formed material, all were first in the condition of clear, transparent, structureless, formless living matter."75 So Ranvier :76" Cellular elements possess all the essential vital properties of the complete organism." And Allman, in his address as President of the British Association last year, is still more explicit.77 "Every living. being," he says, "has protoplasm as the essential matter of every living element of its structure." "No one who contemplates this spontaneously moving matter can deny that it is alive. Liquid as it is, it is a living liquid'; organless and structureless as it is, it manifests the essential phenomena of life." "Coextensive with the whole of organic nature every vital act being referable to some mode or property of protoplasm, it becomes to the biologist what the ether is to the physicist." From these quotations it would seem that even in the highest animal there is nothing living but protoplasm or germinal matter, "transparent,

colorless, and, as far as can be ascertained by examination with the highest powers of the microscope, perfectly structureless. It exhibits these same characters at every period of its existence." Neither the contractile tissue of the muscle, the axis-cylinder of the nerve, nor the secreting cell of the gland, is living, according to Beale.78 Hence it would be fair to draw the inference that vital force should not be required to explain the phenomena of the non-living matter of the body, such as the contraction of the muscle or the function of the nerve. If this be conceded it is a great point gained; since the phenomenon of life becomes vastly simplified when we have to account for it only as exhibited in this one single form of living matter, protoplasm. In describing its properties, Allman includes this remarkable mobility, these spontaneous movements, and says that they result "from its proper irritability, its essential constitution as living matter." "From the facts there is but one legitimate conclusion, that life is a property of protoplasm." Beale, however, will not allow that life is "a property" of protoplasm. "It cannot be a property of matter," he says, "because it is in all respects essentially different in its actions from all acknowledged properties of matter."79 properties of bodies are only the characters by which we differentiate them. Two bodies having the same properties would only be two portions of the same substance. Because life, therefore, is unlike other properties of matter, it by no means follows that it is not a property of matter.80 No dictum is more absolute in science than the one which predicates properties upon constitution. To say that this property exhibited by protoplasm, marvellous and even unique though it be, is not a natural result of the constitution of the matter itself, but is due to an unknown entity, a tertium quid, which inhabits and controls it, is opposed to all scientific analogy and experience. To the statement of the vitalist that there is no evidence that life is a property of matter, we may reply with emphasis that there is not the slightest proof that it is not.

Chemistry tells us that complexity of composition involves complexity of properties. The grand progress which Organic Chemistry has made in recent times has been owing to the distinct recognition of the influence of structure upon properties. Isomerism is one of its most significant developments. The number of possible isomers increases enormously with the complexity of

the molecule. Granted that we now know several of the proteid group of substances:81 how many thousands may there be yet to know? Bodies of such extreme complexity of constitution may well have an indefinite number of isomers. Not only does chemistry not say that there cannot be such a thing but she encourages the expectation that there will yet be found the precise proteid of which the phenomena of protoplasm are properties. The rapid march of recent organic synthesis makes it quite certain that every distinct chemical substance of the living body will ultimately be produced in the laboratory;82 and this from inorganic materials. Given only the exact constitution of a compound, and its synthesis follows. When therefore, the chemist shall succeed in producing a substance constitutionally identical with the protoplasmic mass, there is every reason to expect that it will exhibit all the phenomena which characterize its life; and this equally whether protoplasm be a single substance or a mixture of several representative substances.

But here a word should be said concerning a remarkable physical condition assumed by matter in organized beings. Graham, in 1862, drew the sharp line which separates colloid from crystalloid matter.83 His researches have proved, says Maudsley,84 the necessity of considerable modification in our usual conception of solid matter. Instead of the notion of inert impenetrable matter, we must substitute the idea of matter which in its colloidal state is penetrable, exhibits energy, and is widely susceptible to external agents; its existence being a continued metastasis.' This sort of energy is not a result of chemical action, for colloids are singularly inert in all ordinary chemical relations, but is a result of its unknown molecular constitution; and the undoubted existence of colloidal energy in organic substances, which are usually considered inert and called dead, may well warrant the belief of its larger and more essential operation in organic matter in the state of instability of composition in which it is when under the condition of life. Such energy would then suffice to account for the simple uniform movements of the homogeneous substance of which the lowest animal consists; and the absence of any differentiation of structure is a sufficient reason for the absence of any localization of function and of the general uniform reaction to different impressions." Graham himself says that the colloidal state may be looked upon "as the probable primary source of the force appearing in the phenomena

of vitality."85 The colloidal condition is the dynamical state of matter; the crystalloidal the static. The former, which is the rule in the organic kingdom of nature, is the exception in the inorganic. Aluminum and ferric hydrates, silicic acid and a few other inorganic substances, exist in the colloid condition. From analogy there would seem to be but little doubt that the colloid state of these bodies differs from their crystalloid state merely in the size of the molecule. In other words opal, which is colloid silica, is a polymer of quartz. If this theory be true there can be no doubt of the vastly greater complexity of a colloidal proteid molecule than of a crystalloid one. Now it is a very significant fact, in this connection, that not a single organic colloid has ever been synthesized. Gelatin, which is one of the best examples of a colloid, has a comparatively simple structure. And, although Hunt suggested, many years ago, that gelatin was probably an amidoderivative of the sugar group,86-a theory subsequently partially confirmed by Gibbs-yet no inverse process has yet given us this substance. That matter in the crystalloid and the colloid forms may be chemically identical, differing only in the size of its molecule, may be quite possible. But it is also possible that the difference may be a physical one. To produce the colloid state from the crystalloid is by no means beyond the power of science. We qualify our previous statement then only so far as to say that when the chemist produces a body in the colloidal form, having the identical constitution of protoplasm, there is every reason to believe that it will have the vital properties of protoplasm.

The important question now arises whether, since the protoplasm of animals is identical with that of vegetables, and the latter is the food of the former, any energy whatever is stored up by the animal as such. That this identity exists would seem satisfactorily established. Though the protoplasm of vegetables is enclosed within a cellulose bag, it is, says Allman, only a closely imprisoned rhizopod.87 In the Nitella, it shows all its characteristic irritability, and from Vaucheria it escapes to exhibit all its amoeboid movements. Spores swim about by cilia or flagella, and the cell-division of the one kingdom is the same as that of the other. In plants, however, protoplasm seems to be associated with chlorophyll, whose function was for a long time supposed to be to decompose carbon dioxide under the influence of sunlight. But Draper in 1872, showed that this decomposition took place before the chlo