898 NUTRITION AND HEAT REGULATION. 



since the proteins are the most expensive foods, and in the feeding 

 of large masses of individuals — armies, schools, asylums, etc. — ■ 

 it is not desirable to waste money on protein food if it is not 

 needed. The full and satisfactory answer to this question must 

 be deferred until more experience is obtained. The report upon 

 the Bengalis, noted above, would seem at first to constitute a 

 satisfactory demonstration of the practicability of a low protein 

 diet, but McCay states that the Bengah is inferior physically to 

 the average European, and is particularly deficient in capacity 

 for muscular work, and he is inclined to attribute this inferiority 

 to the diet. Moreover, the Bengali is quite susceptible to kidney 

 troubles, a fact which seems to destroy one prediction often 

 made by those who advocate a low protein diet, namely, that the 

 smaller amount of work thus thrown on the kidneys would result 

 in a diminution of diseases of the kidney. The newer conceptions 

 in regard to the digestion and nutritive history of the protein 

 foods certainly seem to favor the adoption of a low protein diet. 

 If protein is eaten in excess of the real assimilation needs of the 

 tissues, all the excess, so far as we can see, might just as well be 

 substituted by carbohydrate or by carbohydrate and fat. The 

 excess nitrogen thus eaten appears to be so much useless ballast 

 which the body very promptly gets rid of, although it must be 

 remembered that the ammonia formed in the process of deaminiza- 

 tion plays a most useful role in neutralizing the acids formed in the 

 body. The uncertain point, however, is what constitutes the assimi- 

 lation need of the tissues. The experiments given above would place 

 this need very low, according to the lowest estimate at about 5 per 

 cent, of the total energy value of the food. That is to say, if the 

 daily diet contains heat energy equivalent to 2400 calories, only 

 5 per cent, of this, 120 calories, needs to be in the form of protein, 

 an estimate which would bring the protein to about 30 gm. 

 daily. Many objections have been urged against the attempt to 

 apply this apparently logical conclusion to public dietaries. We 

 are reminded that our knowledge of the details of the metabolism 

 of protein is very incomplete, and it is not certain yet that in 

 the long run a low protein diet would be entirely without injury. 

 Emphasis has been laid also upon the importance of providing 

 what Meltzer has named a ''factor of safety," that is to say, a 

 certain margin beyond a bare suflEiciency which will be a reserve 

 against unusual demands, but this objection simply serves to re- 

 state the question. If a man is accustomed to eat 100 gm. of 

 protein daily and science demonstrates that he can maintain a 

 nitrogen equihbrium on 30 gm., does a reasonable factor of safety 

 require the use of the additional 70 gm., or would perhaps a 

 total of 50 or 60 gm. per day meet every requirement? It seems 



