898 NUTRITION AND HEAT REGULATION. 



monia salt in the diet, to produce an amino-acid, according to the reversible 

 equation 



CH 3 CHNH 2 COOH + H 2 O * CH 3 CHOHCOOH + NH 3 . 



If this is true, then it might follow that an inorganic salt of ammonia could 

 under certain conditions supply the nitrogen necessary for the construction 

 of body-proteins, or at least for some of the amino-acids concerned in this 

 synthesis. The matter is still under investigation. Some observers (Under- 

 bill and Goldschmidt, "Journal of Biological Chemistry," 15, 341, 1913) 

 state that there is a difference in this respect between the inorganic and 

 organic salts of ammonia so far as the animal body is concerned. With the 

 inorganic salts (ammonium chlorid) and non-protein food no evidence can 

 be obtained of the utilization of the ammonia. With the organic salts, on the 

 contrary (ammonium citrate or acetate), there is a marked decrease in the 

 nitrogen loss when the animal receives in addition only non-protein food. 

 Other observers, however, doubt the application of these results to normal 

 nutrition. It is possible, for example, that the utilization of the ammonia 

 salts may be effected indirectly through bacterial action in the intestines. 



The Amount of Protein Necessary for Normal Nutrition. 



As was stated above, nitrogen equilibrium may be maintained on 

 different amounts of protein food. It is important, from a 

 scientific and from an economic standpoint, to determine the low 

 limit for this equilibrium and to ascertain whether, for the purpose 

 of the best as well as the most economical nutrition, this low 

 limit is as good as or preferable to a higher amount of protein in 

 the diet. Examination of the dietaries of civilized races shows 

 that, on the average, 100 to 120 gms. of protein are used daily by 

 an adult man. Voit gives 118 gms. of protein as the average 

 daily consumption. A variable portion of this amount passes 

 into the feces in undigested form, but we may assume that about 

 100 to 105 gms. are absorbed and actually metabolized in the body. 

 If we take into account the weight of the body, this amount of 

 protein may be estimated as equivalent in round numbers to 

 1.5 gms. of protein (or 0.23 gm. nitrogen) per kilogram of body- 

 weight. In recent years serious attempts have been made to 

 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 



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

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

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



