FOOD AND DIGESTION 73 



expensive, both in actual cost and, possibly, on account of 

 its influence on the cells of the animal using it, the ques- 

 tion has arisen whether we could not advantageously re- 

 duce the amount in our diets. It has, indeed, been shown 

 that for considerable periods of time the amount may be 

 reduced to less than a half of the amount given in the 

 dietaries above with no apparent impairment of the per- 

 son's health or efficiency. Against this, however, is the 

 fact that, left to himself, normal man takes the larger 

 amount of protein in his diet, regardless of his condition 

 or occupation. When one is engaged in work necessitating 

 much muscular exertion, a greater number of calories is 

 required, but when this is the case, the increase is made 

 largely with the carbohydrate and fat, the laborer using 

 actually little more protein than the clerk who leads a 

 sedentary life. 



Since urea, resulting from protein decomposition in 

 the body, is excreted by the kidneys, it has been sug- 

 gested that large amounts of protein in the diet will 

 throw extra work on these organs and tend to injure 

 them. Then, too, it has been pointed out that the putre- 

 faction of proteins that may take place in the intestines, 

 gives rise to poisonous substances, which entering tiie 

 circulation, may damage both liver and kidneys. These 

 are theoretical conditions, however, which are still far 

 from proved. 



Tn some recent work, it has been pointed out that not 

 all proteins are li adequate" for nutrition. It is essen- 

 tial that certain of the "building stones" be present, 

 and if the protein is deficient in these it does not suffice 

 for the purposes of maintenance or for the promotion of 

 growth. Gelatin is an illustration of one of the inade- 

 quate proteins. It was formerly believed that gelatin 

 was capable of supplying the protein in the diet, and 



