GENERAL METHODS HISTORY OF PROTEIN FOOD. 907 



ascertain how low this daily quota of protein may be reduced 

 without destroying nitrogen equilibrium or injuring the effective- 

 ness of the body for muscular or mental work. Siven was able 

 for short periods to reduce his daily diet" of protein to as little as 

 0.5 gm. (0.08 gm. N.) per kilo of body weight, but probably the 

 most important experiments of this kind are those carried out 

 by Chittenden.* In this work the experiments were continued 

 over long periods of time, and were made upon three different 

 groups of men, five university teachers, a detail of thirteen men 

 from the Hospital Corps of the Army, and eight university students 

 classed as athletes. The general result of the investigation 

 showed that the body can be maintained in protein equilibrium 

 and in a normal state of efficiency upon a diet containing only 

 30 to 50 gms. of protein per day, according to the weight of the 

 individual or, expressed in more general terms, the daily quota 

 of protein per kilo of weight may be reduced from 1.5 gms. 

 (0.23 gm. N.) to about one-half, that is, 0.75 gm. of protein or 

 0.12 gm. of nitrogen per kilo. This general result has been 

 confirmed on a large scale by the studies made by McCayf of 

 the metabolism of the Bengalis of India. He finds that the 

 average Bengali metabolizes in his body, so far as may be judged 

 from the nitrogen excreted in the urine, only about 37.5 gms. of 

 protein daily, corresponding to a consumption per kilo of 0.7 gm. 

 of protein or 0.113 gm. of nitrogen. A corresponding average 

 amount of protein is, of course, eaten daily, and on this low pro- 

 tein diet they exist in apparent health. RubnerJ also empha- 

 sizes the fact that milk, which forms the sole diet of the infant, is 

 a protein poor food. The usual daily diet of the adult has a heat 

 value of from 2400 to 3000 calories (see p. 952). Of this total 

 heat value the protein food in the diets usually recommended 

 forms about 15 to 20 per cent. In milk, however, according to 

 Rubner's estimates, the protein constitutes only about 10 per 

 cent, of the total heat value. As the result of these and similar 

 investigations, the practical question presents itself as to what 

 constitutes the optimum daily quota of protein. If the body can 

 be kept in good condition upon 0.75 gm. per kilo per day, will an 

 ingest ion of more than this, say twice as much, prove injurious 

 or beneficial or indifferent to the body? Outside its hygienic 

 aspect the question is important from an economical standpoint, 



* Consult Chittenden, "Physiological Economy in Nutrition," New York, 

 1905, for discussion and literature. See also Hinhede, "Skandinavisches Ar- 

 chiv. f. Physiol.," 30, 97, 1913. 



t McCay, "The Metabolism of the Bengalis, Calcutta," 1908. (Scientific 

 Memoirs, Medical Department Government of India, No. 34.) Also later 

 report upon Jail Dietaries, ibid., No. 37, 1910. 



t Rubner, "Das Problem des Lebensdauer," 1908; Cohnheim, "Die Phys- 

 iologic der Verdauung u. Ernahrung," 1908. 



