which these phenomena are produced. Respecting the nature of life in the second sense two opinions are at present held. The first, which is that maintained by Dr. Beale, is the hypothesis that a peculiar vital force or principle animates each living being, and produces in it that part of the phenomena which cannot be accounted for by the operation of the physical forces of inorganic nature. Thus the motion of a living body is accompanied by an expenditure of nervous force-which is probably of the same fundamental character as the forces of inorganic nature;--digestion arises from nervous influence and the properties of the gastric juice but over these and the other processes is set a vital force. This preserves the balance of the organism by regulating them, and directing their action to a common end. It is called vital force to indicate that it is the source of formally vital phenomena, and to distinguish it from the forces which are treated of in general physics, and are denominated physical forces. It is supposed to be in its nature fundamentally different from physical force or forces; for to explain phenomena which cannot be accounted for by physical forces we need, not something which merely follows their laws, and consequently would explain nothing which they would not explain as well, but something which shall co-ordain and regulate their action as it were from above. This vital force cannot, indeed, create the chemical elements or physical forces with which it has to deal, but the changes continually going on in the organism place in its hands a store of physical force which it can apply to this or that purpose, according to the needs of the living whole. And therefore its activity neither increases nor decreases the total quantity of physical force existing in the universe. The second opinion denies the existence of any such vital force as has been just described, and attributes vital phenomena to the operation of the physical forces; it is therefore called the physical theory of life. On behalf of this theory it is argued that to pretend to explain the action of the varied and complicated machinery which dissection and the microscope show to be at work in a living body by attributing them to the operation of a "vital principle," is as if a visitor to a cotton factory "were to give up in despair any attempt to acquaint himself with the meaning of the several processes that go on before his eyes, and were to regard it as a sufficient account of the transformation of raw cotton into a woven material, that it takes place by the agency of a calico-making principle." It is pleaded that in every case where an explanation has been given of any phenomenon occurring in a living being, it has been explained by showing it to be produced by the operation of the forces of inorganic nature and of nerve-force-a force working through organized matter of a peculiar kind (nervous tissue), but correlated with the other forces; and that as science advances the other vital phenomena will, if they are to be explained at all, be explained in the same manner. A plant or animal is, therefore, only a very complicated machine, and the effects seem to be wonderful, and the explanation is difficult, only because the complication is immense.

Which of these opinions is the correct one-what is in reality the nature of the agency by which vital phenomena are produced-can obviously be decided only by examination of these phenomena. And when we proceed more carefully to examine them, there are two things which at once fix our

attention the first, the extraordinary character of the phenomena themselves; and the second, the extraordinary character of organisms, in which alone they take place. Of the phenomenal definitions of life, consequently, some have drawn attention specially to distinctive characteristics of organisms or bodies of plants and animals, as, "life is the sum of the phenomena proper to organized beings;" others to distinctive characteristics of vital phenomena, as, "life is a general and continuous movement of combination and decomposition." But great difficulty has been found in constructing any definition which will include all that is alive, and exclude all, that is not.

However, the most superficial observation of any living being through a considerable space of time discloses phenomena which even to the most thoughtless are so strange, and are so different from what we find in inorganic nature, as abundantly to warrant the appellation, "The Mystery of Life." Any inorganic object, as a crystal, a stone, a lump of iron, a machine, remains the same only so long as it continues to be composed of the same particles of matter; add to or remove from a watch a spring, a wheel, a lever, and its properties and powers are pro tanto altered. On the other hand, an animal or a plant continues to present the same appearance-to sleep and to feel and move in alternate periods, to bear leaves, and flowers, and fruit, in recurrent seasons,—not merely in spite of, but only on condition of continual renewal of its particles; and if this renewal is prevented for any length of time, a thorough and radical change takes place, and it is resolved into a mass of putrescence. Breathing and the ingestion of food continually convey into the body new matter which becomes an integral part of it; secretions and excretions continually carry away matter which was formerly an integral part of it; by these means, indeed, the entire organism may in some species be several times wholly renewed in the course of its existence; and this characteristic of life has suggested the second definition quoted above. We live only because we do not continue the same. Every living organism is in fluxu, and it is this very fluxus that ensures its persistent existence. Again, a non-living object is modified in exact proportion to the quantity and intensity of the external influences acting on it. The degree to which a spring is bent is a test of the pressure brought to bear on it; the increment of motion in a moving body is a test of the attractive force which draws it on; the distance to which the pith ball of an electrometer is repelled from the stem indicates, as precisely as humidity in the atmosphere and accidental mechanical imperfections in the instrument allow of, the tension of the electricity present. But it is not so with a living being. It possesses an internal activity able, within wide limits, to resist the action of external influences; 'and when these without, or morbid agencies within, become too strong for it, it breaks down altogether, and death ensues. The temperature of the blood, for instance, is almost the same in the coldest as in the hottest climates. That which lives is continually exercising over itself a regulative power, and increasing or diminishing, as may be needful, the intensity of the processes going on within it. The heart beats more forcibly when disease of its valves offers any considerable impediment to the circulation. The blood is directed with greater force

and in greater quantity to the organs which are working than to those which are at rest. The secretion of gastric juice is regulated by the presence and quantity of food in the stomach. A living being possesses also a reparative power for healing injuries experienced by it, while no non-living product of nature can repair those which may be done to it. The healing of a wound, the growing together of the two ends of a fractured bone, convalescence from an illness, have no parallels in the inorganic world. Further, a living being has that most marvellous power of producing others the same in species with itself. It may be added that, at least, in the higher orders of plants and animals, which exhibit the phenomena of life in greater complexity and abundance, species are so rigid, resist external influences so obstinately,— that all their members will die rather than become essentially modified by their environment. And even if it be granted to the disciples of the Darwinian that one species can be changed into another, the immensity of the time postulated brings the admitted rigidity of species into the strongest relief. Again, the duration of the life of a living being is not indefinite. It may continue to live for more than a hundred years, although of soft consistency and almost infinite complexity, its delicate fabric sustaining during that time a continual friction arising from voluntary and involuntary movements. But even if it be not destroyed or injured by accidental causes, vital phenomena manifest themselves in it for a period only about four times as long as that occupied by its growth and development. And these vital phenomena pass through a definite cycle. It grows and consolidates in infancy, childhood, and adolescence; remains for some time in full possession of its powers; and then becomes gradually weaker with declining years, until the descent is closed by death. It begins its distinct existence as a minute germ (the germinal spot), so small that it cannot be seen by the naked eye; and when it is made discernible by the microscope, it is but a clear homogeneous spheroid as structureless as a drop of water. It is, however, placed in juxtaposition to nutritive material, and absorbs it into itself until it is millions of times, perhaps, its original bulk; but, wonderful to say, it does not pass over to the nature of that which it absorbs, but assimilates it to itself, and by its inherent power places it here or there, and changes it thus or thus, so as to form itself into an organism of marvellous harmony and complexity, and resembling its parents, often in most minute particulars. And neither to the manner in which the organism is formed, nor to the nature of the organism which is formed, is there any parallel in the inorganic world. The best definition of an organism is probably the teleological one suggested by Kant; "an organized product of nature is one in which all the parts are reciprocally ends and means." Thus the muscles, which are the organs of motion, and those of special and general sensation, e.g., eyes, ears, and skin, whose behests it is the function of the greater part of them to carry out, evidently subserve the general good of the organism by assisting in supplying it with food and protecting it from incidental dangers. On the other hand, the nourishment of the immense mass of muscular substance purifies the blood by abstracting from it elements which, if retained, would render it unfit to be the pabulum of other organs. The same may be said of the adipose tissue, which at the same time serves as a reserve of heat, providing nourishment against time of need; of the horny

matter of the nails and hair, the former of which protect the extremities, while the latter afford protection against climate; of the bile secreted by the liver, which secures digestion; and of the calcareous matter of the bones and teeth, which remaining in the blood would produce diseases of the bloodvessels, as it does in old age, but passing on to the bones is the source of their necessary firmness; so that, generalizing, it has been held that there is, as it were, a balance of organs, and that every organ is a secretion with respect to every other. The nervous system exercises a sort of general supervision over all the organism; in return, the whole of the organism combines to support the nervous system. The circulatory system provides the digestive organs with the nourishment necessary to the fulfilment of their functions; the digestive organs furnish the materials of the blood. The body of man is like his mind; no part of it continues to function normally except the others do so also. Each part is the servant of the whole; and the whole feels with, and in case of necessity comes to the assistance of, any of the parts.

Such are the most prominent and obvious characteristics of life. They do not belong to this living being and to that, but, mutatis mutandis, to all living beings whatsoever. They belong to nothing that is not alive. Their peculiar and distinctive character raises a very strong initial presumption against any opinion which asserts that the physical forces of inorganic nature are the cause of vital phenomena, and at once throws a heavy burden of proof on those who declare this to be the case; and although some approach to some sort of a physical explanation of some of them may to some extent be made, this is as far from a fairly complete explanation of vital phenomena in their integrity as the piers and jetties of the opposite harbours of two continents are from bridging over the ocean which rolls between them. The continuance of the living being under varying external conditions, and still more the reproduction of plants and animals the same in species for at least many generations, are, to say the least, almost incredible, if we do not recognize the existence of an internal regulating principle set over the physical processes to direct and co-ordain them.

How, then, is this initial presumption met by those who hold the physical or molecular theory of life? In the first place, they attack the opposite theory. Dr. Gull, for instance, in his "Oration," declares that "They who maintain the hypothesis of a separate vital force, independent of the ordinary forces of nature, and which has no special relation to them, do, by the very terms of the hypothesis, assume that the phenomena of living beings are out of the proper range of science, and they consign us to a perpetual mental inactivity and ignorance in that region of knowledge in which, above all others, man is interested." But the amount of residual phenomena which require some further and non-physical agency to explain them, can be determined with precision only by exact knowledge which and how much of the total phenomena occurring in a living being can be explained by causes merely physical. While, therefore, the molecularist enters on the investigation of phenomena with a bias arising from a foregone conclusion as to the kind of cause to which he is to refer them, vitalism equally incites to the study of the phenomenon, but leaves the investigator free to refer any particular

phenomenon either to a physical or a vital agency; for no one supposes that everything which takes place in a living organism is to be ascribed to its vital force, nothing to physical forces. Even if a person attributed the manufacture of cotton to a calico-making principle, that need not prevent him from examining the nature and action of the machinery, which would according to him be the means by which that principle worked. He would, in fact, from the nature of the machinery, see that it required some regulative principle, and he would find that principle in the body of workmen attending to the mill. It is also argued that certain of the phenomena which occur in living beings have been accounted for by the operation of the physical forces, and that consequently the rest are to be explained in the same manner. This, however, assumes that all the phenomena are of the same nature as those which, it is asserted, have been thus explained. This is the very point at issue; and if some aspects of some phenomena presented by living organisms have been accounted for by the operation of physical forces, there are always other aspects which cannot be so accounted for. It is urged also that the molecularist theory is more in accordance with the present tendencies of science than vitalism is-i.e., the present tendency of science is to explain phenomena by reference merely to matter and motion, and it is more in accordance with this tendency to explain life by matter and motion than to explain it in any other way. But this, as Dr. Beale very truly says, is only the constantly recurring dream about unity,-the idea that all phenomena, whether of inorganic nature, or life, or mind, are the results of some one universal law, stealthily influencing even modern and scientific thought. And this old dream of unity is distinctly unscientific.*

In the second place, when the advocates of the physical theory of life endeavour to substantiate it, they do so not by proposing evidence in its favour, but by treating us to apologies for the lack of evidence, to dogmatic assertions, prophecies, suppositions, and vague language conveying no definite information. We are told, for instance, that if certain kinds of matter manifest vital phenomena, this is because of "their molecular machinery, worked by their molecular forces." This would be all very well as a sentence introductory to a description of the machinery and the forces, showing them to be such as would produce the phenomena in question. But, as it stands, it is on a par with, e.g., an assertion that the battle of Waterloo was lost by the French because of the state of the weather, made by a person ignorant what the state of the weather was, and ignorant what influence it had, if any, on the defeat of the French army; for it is at the same time admitted, that of this molecular machinery not a trace has ever been seen, that only the merest generalities can be inferred about it, and that these generalities are even ludicrously insufficient to form the basis of a train of reasoning of which the physical theory of life shall be the conclusion. If we complain of this, we are told, with perfect justice, that it arises from the inherent difficulties of the subject -from the extreme minuteness of the molecules, the scanty and precarious

* Mill's Logic, Book iii. ch. xiv. § 7.