404 POPULAR SCIENCE MONTHLY 



to the same group. The specificity of enzymes, however, extends 

 farther than this, being intimately connected with the chemical con- 

 figuration of the molecule acted upon. As a rule, generally accepted 

 to-day, it is understood that living organisms, both animal and vege- 

 table, work mainly with optically active carbon compounds, i. e., com- 

 pounds 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 reason- 

 ing, 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 demon- 

 strations and who were moreover dominated by the prevalent belief in 

 the spirits provoked from him this statement : 



With reference to the third point, or that of the spirits, it may be said 

 tnat, as it is still a question what they are, how extant in the body, of what 

 consistency, whether separate and distinct from the blood and solids, or mingled 

 with these — upon each and all of these points there are so many and such 

 conflicting opinions, that it is not wonderful that the spirits, whose nature is 

 thus left so wholly ambiguous, should serve as the common subterfuge of 



