PROBLEMS IN NUTRITION 329 



This amount, indeed, is rarely exceeded, for Chittenden has shown 

 that even the diet of well-to-do Americans, which appears to us as 

 the richest in proteids, scarcely ever exceeds 100 gr. of proteids a day, 

 and the investigation of the freely-chosen fare of the most various 

 individuals leads to the same result. 



The question as to the need of the human body for 100 gr. of pro- 

 teinaceous material per day has often been raised ; and even to-day 

 cannot be answered with certainty. During the last years, however, 

 we have learned of a series of reasons which may serve to throw some 

 light upon the subject. 



That the growing organism requires proteids is self-evident, for in 

 this way only can it obtain the materials of which it is composed. 

 We know further, however, that the adult organism continually 

 repairs and increases its organs and consequently also requires pro- 

 teids. According to Zuntz a man increases his muscles when he does 

 unaccustomed work (for example, when he learns a new sport) or even 

 by increased exertion upon his usual work. Bunge attributes a con- 

 siderable requirement of proteids in adults to the loss of organ- 

 proteids in the sperm of man, and to menstruation, pregnancy, and 

 lactation in woman. And later years have disclosed the genetic 

 relations of many decomposition-products of the proteids with carbo- 

 hydrates, with substances of the bile, and others, which are necessary, 

 at any rate for a time, to neutralize poisons, or which are essential 

 for the intermediate metabolism; and these relations appear to render 

 desirable at least the presence of a copious supply of proteinaceous 

 material. 



A second reason is more difficult to grasp. Even the first metabolic 

 experiments of Voit showed that although the proteids possess no 

 higher nutritive (fuel) value than the carbohydrates, and a very much 

 smaller nutritive (fuel) value than the fats, they burn very much 

 more rapidly; and this has since been repeatedly confirmed. When 

 the supply of proteids in the food is increased above the actual need 

 of the body, the fats and carbohydrates are stored up, and the pro- 

 teids are burned to a very much greater extent. The relations between 

 the cells of our bodies and the substances absorbed as nutriment can 

 best be illustrated by an analogy. For the neutralization of an alkali 

 any acid may be employed; but when several acids of differing 

 strength are present together, the strongest one will be partially 

 saturated before the others even begin to react. In the same way 

 protoplasm can supply its need with all three nutritive substances; 

 but when all three are present at once the proteids burn first. With 

 a large excess of the other two, however, the action of their masses 

 becomes evident, exactly as in the illustration with the acids, and 

 they protect the proteids from combustion. In the absence of fats 

 and carbohydrates, the body readily goes into such a state that its 



