THE METABOLIC REQUIREMENTS OF THE BODY 1057 



of protein which must be ingested in order to bring a person into nitro- 

 gen-equihbrium. To attain this end we need 30 grm. of the proteins 

 of meat, 31 grm. of the proteins of milk, 54 grm. of the proteins of beans, 

 76 grm. of the proteins of bread, and 102 grm. of the proteins of corn. 

 This outHne shows very clearly that the proteins of the vegetables 

 are not so easily assimilated as those of meat. 



Excessive Metabolism. — The body safeguards itself against possi- 

 ble disorders in its metabolism first by the quality and secondly, by the 

 quantity of the food. It constantly endeavors to retain a normal 

 balance sheet. Under ordinary conditions, however, more material 

 is ingested than is actually required to preserve its metabolic equi- 

 librium. This fact has led some physiologists to believe that a certain 

 luxus consumption is a necessity in order to allow for a definite waste. 

 Any excessive ingestion, on the other hand, leads as a rule to a certain 

 deposition of the superfluous material in the tissues. Thus, if a 

 normal animal is given excessive amounts of fats and carbohydrates, 

 a large portion of these, foodstuffs is converted into glycogen and 

 tissue-fat without materially increasing the general metabolism. In 

 the case of hyper amounts of proteins, however, no significant storage 

 takes place, and by far the largest part of this substance is excreted 

 directly. Consequently, the output of nitrogen may be employed 

 as an index of the amount of proteins ingested. 



This fact shows very clearly that a luxus consumption in the case of 

 proteins cannot serve an important purpose, and is very expensive be- 

 sides. Chittenden has proved that a normal nutritive condition may be 

 attained on a mixed diet containing only 7 grm. of nitrogen daily. Men 

 partaking of this diet followed their ordinary vocations without diflS- 

 culty, and yielded from 32 to 35 calories per kilo of their body-weight. 

 In fact, when somewhat larger quantities of carbohydrates and fats 

 were given, the nitrogen ingo could be reduced to 5 grm. daily (33 

 grm. of protein). While these experiments indicate that a normal 

 person can get along with less protein than he usually takes, the ques- 

 tion as yet to be decided is: should he actually so deprive himself 

 for his own benefit ? Quite aside from an actual luxus consumption, 

 the answer might be that a material reduction in the ingo of pro- 

 tein material would undoubtedly lower the resistance of these persons, 

 at least in the course of time. Much also depends upon the quality 

 of the protein. The accepted view, however, is that a reduction in 

 the intake of proteins of one-third to one-half might be effected without 

 injury and, naturally, this necessary minimum of about 50 to 60 

 grm. of proteins, instead of the usual 100 to 150 grm., must be sup- 

 plied in the form of meat and vegetables to the exclusion of neither. 

 As has been stated above, much larger amounts of the latter must be 

 ingested in order to furnish the same amount of energy. 



The foregoing discussion must have shown that an animal may be 

 in nitrogen-equilibrium and not in carbon-equilibrium. The latter, 

 however, is not so important, because the quantity of fat may vary 



67 



