to the same group. The specificity of enzymes, however, extends farther than this, being intimately connected with the chemical configuration of the molecule acted upon. As a rule, generally accepted to-day, it is understood that living organisms, both animal and vegetable, work mainly with optically active carbon compounds, i. e., compounds in which there is at least one asymmetrical carbon atom. As Kossel has expressed it, the asymmetry of the cell building stones begins the moment of the assimilation of carbon dioxide from the atmosphere by the chromophyl-containing plant cells, from whence it is carried directly to the herbivorous and indirectly to the carnivorous animals. In other words, enzymolysis as it occurs in the animal body is bound up with the chemical constitution and configuration of the substances undergoing change, so that only those substances can be transformed or decomposed that have a certain definite plan of structure. It is thus clear that the processes of nutrition are carefully ordered and clearly defined, while to follow their many paths and interpret aright the signs by the roadside requires accurate chemical and physiological knowledge.
From the early conceptions of nutrition as embodied in the work of Lavoisier and his immediate successors, we have traveled a long way. From vague generalizations based on erroneous views and faulty reasoning, we have passed to a period of scientific activity, where thoughtful observation and careful analysis have contributed to a broader and clearer understanding of the ways of nature. New points of view lie before us pregnant with meaning and full of suggestions for future work. Let us gather together all the facts available, search far and near for all the data that can be obtained bearing upon the question at issue, remembering that progress can come only from intensive and persistent investigation, and that conclusions bearing the imprint of truth must be based upon accurate knowledge. It is only when we lack knowledge that we are liable to be led astray by vain imaginings. How clearly this is illustrated by the experience of the renowned Harvey who when he was arriving at a true understanding of the circulation of the blood, by patient inquiry and still more patient dissecting, was constantly confronted by the crude and illogical views based entirely upon the speculation then prevalent! His many critics who lacked sufficient knowledge to be impressed by his careful demonstrations and who were moreover dominated by the prevalent belief in the spirits provoked from him this statement: