belief that the quantitative needs of the body for protein food are more satisfactorily met by a liberal addition of vegetable matter with its larger calorific or heat-producing power and smaller nitrogen content. In view, however, of what has been stated concerning the divergent chemical structure of individual proteins, it is obvious that a new standard of comparison is at hand, the suggestions it may offer to be tested by appropriate feeding experiments on man and animals. Truly, no chapter of nutrition is more deserving of careful consideration, both from a scientific standpoint and from its bearing on the welfare of the human race, than that which deals with the relative capabilities of the various proteins of animal and vegetable origin.
In all that has been said we see emphasized the ability of the living organism to break down its complex food material, as well as the corresponding material of its tissues and organs, into the simplest of chemical fragments, coupled with the capacity to construct equally complex tissue material out of the fragments so produced. Profound and progressive hydrolysis, rather than simple oxidation, is the method of decomposition, for many of the fragments at least are to be carefully conserved for future use. Oxygen, however, may play its part in connection with the smaller groups, though even here enzyme intermediation may still be found a ruling factor. Enzymes are to be detected on all sides, both inside and outside the cells of the individual tissues and organs, and it is through their agency that the varied processes of life are carried forward. The present realization of the profound part played by enzymes in the reactions of the animal body is completely transforming our views of life. The so-called vital activities of living tissue or its component cells are no longer shrouded in that mystery which defies explanation, but we see within our reach tangible means of unraveling the complexities of cellular activity. One by one, the old views of living matter and organic structure are giving place to truly scientific conceptions that admit of logical interpretation. It is not long since, when chemists and physiologists alike viewed with enthusiasm, akin to awe, the production of an organic compound by synthesis in the laboratory. I well remember meeting the renowned Wöhler, then an old man, in one of my early visits to Göttingen. Yet, Wöhler was the first to make an organic substance by synthesis. Up to his time, physiologists all believed that organic substances, whether simple or complex, could be formed only through the agency of a living organism. To-day, however, there is almost no limit to our power of producing organic substances by purely chemical synthesis. In the hands of the chemist, many of the reactions of living matter may be duplicated and we are led to see that the living organism makes use of processes which are merely a counterpart of those we have learned to control in the laboratory.
