carried on from the time of Aristotle, who was a thoroughgoing teleologist, to the present, when both sides of the question are represented by able and scholarly defenders. The question at issue is one of fundamental importance, and one to be kept in mind by the reader as he goes through the rest of this volume. When he gets to the end he will possibly be somewhat better prepared to form an opinion on this mooted question.

The fundamental aim of the biologist is to understand the processes of life. Most vitalists, I think, would admit that knowledge of the physical and chemical changes that occur in living tissues would be of the highest importance. Certainly vital activity is conditioned by, if it be not completely explainable in terms of, the physical and chemical properties of the substances constituting protoplasm. I think it must be conceded that a part, at least, of the processes of living are already susceptible of explanation in chemical terms. There may always remain a residue which may serve as a subject for controversy. But if the position of either the mechanist or the vitalist is ever proven to be correct, it can be done so only by an intimate knowledge of fundamental life processes. Whatever standpoint is adopted, we should attempt to explain in mechanistic terms as much of vital activity as possible. For the vitalist, this would serve the purpose of revealing more clearly the elements involved in life, if there really are such, which are not capable of a mechanistic explanation. If all of the life processes are explained in terms of chemical and physical laws, the mechanist has won his case.

We shall not attempt to pursue the varied and subtle modifications of vitalistic theory. Historically the doctrine is a lineal descendant of the animism of primitive man. In the light of advancing knowledge, the cruder forms of vitalism have largely disappeared and have given place to more refined forms less obviously opposed to the results of scientific discovery Many physiologists have felt compelled to appeal to something different from the ordinary forces of nature in order to account for the constructive and coördinating processes of life. It has been asserted that natural forces, left to their own guidance, are ca

pable only of destruction. When life leaves the body, things fall into ruin and decay. Life apparently has to struggle against these forces of nature. Claude Bernard, one of the greatest of physiologists, declared that "vital phenomena have their physicochemical conditions rigorously determined," but at the same time the organism "appears to be directed by some invisible guide in the course which it follows. . . . The vital force directs the phenomena, which it does not create; physico-chemical agents produce phenomena which they do not direct." Bernard, like later vitalists, is desirous of adopting an interpretation of control which does not get him into trouble with the doctrine of the conservation of energy. But can energy be directed and controlled by anything which is not a source of energy in itself? On this question there is no end of subtle discussion. The captain, in controlling the course of his ship, may use relatively little energy, but he must use some. Whether there is a place for real teleological control in a world run, as ours seems to be, in accordance with the rigid laws of matter and motion, will probably be discussed for a long time to come.

REFERENCES

BOSE, J. C., Response in the Living and Non-Living. London, Longmans, 1910.

DRIESCH, H., The Science and Philosophy of the Organism. 2 vols., London, A. and C. Black, 1908-1909.

HUXLEY, T. H., Discourses, Biological and Geological. N. Y., Appleton, 1896.

LOEB, J., The Organism as a Whole. N. Y., Putnam, 1916.

MINOT, C. S., The Problem of Age, Growth, and Death. N. Y., Putnam, 1908.

RITTER, W. E., The Unity of the Organism. 2 vols., Boston, Badger, 1919.

SPENCER, H., Principles of Biology. 2 vols., N. Y., Appleton, 18981899.

THOMSON, J. A., The System of Animate Nature. 2 vols., London, Williams and Norgate, 1920.

VERWORN, M., General Physiology. London, Macmillan, 1899.

CHAPTER II

PROTOPLASM, OR THE PHYSICAL BASIS OF LIFE

The idea that life is everywhere associated with and dependent upon a peculiar substance called protoplasm has become a commonplace in biological thought. It gained wide currency as a result of a famous discourse delivered in 1868 by Professor Huxley, in which he referred to protoplasm as "the physical basis of life." As Professor E. B. Wilson has remarked, in another excellent, though much more recent address on the same topic: "Huxley's presentation of the subject was a masterpiece both of English style and philosophical breadth of outlook. In part for this reason, still more because of its supposedly materialistic implications, it aroused immediate and widespread public attention." But although Huxley disclaimed any belief in materialism, holding it "to involve a gross philosophic error," he failed to forestall a flood of criticism that was directed against him from pulpit and press. The notion that life in man, worm, plant, and protozoön, is in essence the same, and dependent on much the same kind of chemical substances, came as a shock to many of Huxley's contemporaries. But, as is the case with so many other disturbing ideas, now that it has become familiar it is found to be quite innocuous.

In some respects the concept of protoplasm, as presented by Huxley, has been found to require modification. Protoplasm is not a single complex compound, as many of Huxley's statements implied. It is doubtless an aggregation of many complex proteins, together with various other substances, which are equally essential to the maintenance of life. Protoplasm, as Hertwig states, is a "biological concept." And it is not the same chemically in different organisms. Chemical analysis clearly indicates that the component substances found in the protoplasms of the

different forms of life are different both in regard to their more highly organized and unstable protein molecules, and also in regard to their simpler constituents, even down to their prevalent mineral salts. But notwithstanding all these differences, there are many properties of protoplasm which are common to practically all forms of life.

When we look at this physical basis of life under the microscope, we perceive a semi-transparent, jellylike substance, usually part way between the fluid and the solid state. Some

FIG. 1-A, an emulsion of olive oil and water showing a typical foam structure; B, the protoplasm of a radiolarian showing foam structure (from Bütschli); C, a liver cell showing granules. (After Altmann.)

times protoplasm appears, even under the highest powers of the microscope, to be entirely homogeneous. Again, it may have the appearance of a fibrous network; but the most typical structure is that of a sort of foam work, in the cavities, or alveoli, of which there is commonly material of more fluid consistency. The network appearance of protoplasm under a microscope is explained by Bütschli as the result of a foam structure, the walls of the alveoli appearing like interlacing fibers. By making an emulsion of olive oil in a solution of potassium carbonate, Bütschli has produced a fluid which appears under the microscope much like ordinary protoplasm. If very fine particles are added to the fluid, they come to lie in the nodes of the apparent network where

granules are generally found in living substance. The granules. are of very frequent occurrence in protoplasm, and Altmann has advanced the theory that living substance is composed of discrete, but very minute granular elements which he calls bioblasts. Undoubtedly many of the granules observed in protoplasm are formed of living material, although many others represent mere products of protoplasmic activity.

Probably no one of the theories regarding the structure of

FIG. 2-A section across the egg of the worm Chatopterus showing the network structure of nucleus and cytoplasm: A, animal pole; V, vegetal pole of egg; E, granules of the ectoplasm, or outer layer; e.a., e.b., e.c., different kinds of granules in the endoplasm; c, chromatin of the nucleus; n, nucleolus; r.s., nuclear network. (After Lillie.)

protoplasm is universally and exclusively true. Living matter may assume many forms, becoming in different tissues fibrillar, alveolar, granular, or quite homogeneous in composition. Even the same protoplasm may assume different forms at different times. Protoplasm differs greatly in appearance according to