896 NUTRITION AND HEAT REGULATION. 



amino-acids that the nitrogenous material of the body protein is derived. 

 This striking result has led investigators to test whether the body may utilize 

 sources of nitrogen of even simpler construction, such, for example, as the 

 organic or inorganic salts of ammonia. It has long been known that the plant 

 organism utilizes inorganic forms of nitrogen, such as the ammonia salts or the 

 nitrates, in building up its protein, and it has long been believed that the 

 animal protoplasm is not able to utilize these salts in the same way, that, in 

 other words, its processes of synthesis so far as the protein material is concerned 

 are more limited than in the plants. It has been taught universally that ani- 

 mals for the construction of new tissue must have their nitrogenous food in the 

 form of protein, or, a recent addition, in the form of the split-products of pro- 

 tein. Several observers report (see Grafe, "Zeitschrift f. physiolog. chemie.," 

 78, 485, 1912) that when animals are fed upon an abundance of carbohydrate 

 food together with some ammonia salt, such as ammonium citrate, acetate, or 

 carbonate, they may maintain a positive nitrogen balance for long periods. 

 In the metabolism of the amino-acids in the body it is recognized that by 

 deaminization and oxidation an oxyacid or ketonic acid may be produced, 

 and it is suggested that this process may be reversed, that an oxyacid, lactic 

 acid formed from sugar, may combine with ammonia, furnished by an am- 

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

 equation — 



CH3CHNH2COOH + H2O ^ CH3CHOHCOOH + NH3. 



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- 

 vv^eight. In recent years serious attempts have been made to 



