310 HUMAN PHYSIOLOGY 



products. It fails to furnish certain " building stones" 

 which are indispensable. There are a number of 

 vegetable proteins which resemble gelatin in their 

 failure to supply important amino-acids. Their exist- 

 ence was not evident until special studies demonstrated 

 it, because they were found in close association with other 

 proteins of a superior sort from which they had to be 

 separated before they could be tested as individuals. 



As there are proteins which cannot satisfy all the 

 requirements of animal life, so there are others which can 

 do so, but only when consumed in what seems an ex- 

 travagant manner. The trouble with these proteins is 

 that while they give all the needful amino-acids, they 

 yield them in proportions not corresponding to the 

 demand. If the body needs a good deal of an amino-acid 

 which a certain protein furnishes but scantily the total 

 quantity of the protein must be increased until the 

 particular want is met. When this condition is realized 

 there will be an excessive offering of other amino-acids 

 for which the organism has no distinct use. 



In the light of what has been said it should not be 

 suprising to learn that some proteins are much superior 

 to others when the judgment is based on the minimum 

 amount serving to keep a subject from loss of tissue. 

 Generally speaking, the proteins of meat excel those of 

 vegetable origin in their ability to maintain the nutri- 

 tional balance with economy. But the proteins of rice, 

 milk, and potato are nearly as good. Larger quantities 

 of the proteins of wheat and beans must be fed to secure 

 the same result, while the proteins of Indian corn are 

 among the most wasteful which have come under 

 observation. 



It is important that the implications of what has been 

 stated shall not be misunderstood. The facts were 

 ascertained through experiments in course of which 

 volunteers were restricted to one type of protein at a 

 time. We do not commonly limit ourselves in any such 

 a way. Because it takes a great deal of the proteins 



