GENERAL METHODS — HISTORY OF PROTEIN FOOD. 901 



whether gelatin is_ really a nutritious and healthy food. The Academy 

 appointed a commission for the purpose and the report of this commission 

 published m the Annales de Chimie, vol. 92, 1814, was most enthusiastic. 

 Ihey recomniended gelatm as a most nutritious and healthful food, when its 

 natural insipidity was corrected by the addition of salts and savory herbs. 

 On the basis of this report the article was largely used in the nourishment of 

 hospital patients, but in course of time complaints became so emphatic that 

 doubt was again raised as to its real value. In fact, a reaction set in. The 

 second gelatin commission of the French Academy, 1841, a commission of 

 tlie Netherland s Institute, 1844, and a report from the Academy of Medicine, 

 Fans, 1850, all condemned gelatin as useless from the standpoint of nourish- 

 ment, and as mjurious rather than beneficial. Thus, as so often happens, 

 public opmion oscillated from one extreme to the other. The true value 

 of the gelatm, as we understand it to-day, was estabhshed by Voit's experi- 

 ments, but it is e\adent that something remains to be explained. It is not 

 clear why it cannot be borne better in a diet when used in quantity. 



Most suggestive results on this question of the nutritive values 

 of the different proteins have been oljtained in a series of experi- 

 ments reported l^y Osborne and Mendel.* These observers made 

 use of rats, which were fed with a suitable mixture of inorganic 

 salts, carbohydrate, fats, and some single protein representing the 

 sole form in which nitrogenous material was supplied. They 

 found that in addition to gelatin the protein zein obtained from 

 maize, which is deficient in the amino-acids, try]3tophan, lysin, and 

 glycin, is also an inadequate or incomplete protein. Gliadin and 

 hordein which are alcohol soluble proteins obtained from wheat, 

 rye, and barley when fed alone sufficed for maintenance, but not for 

 growth. A young rat fed upon gliadin alone ceased to grow, but 

 did not lose in weight, although the power of growth was not lost, 

 since at any time satisfactory growth could be re-estabHshed by 

 substituting a suitable dietary for the gliadin mixture. By the 

 same method it was shown that the leguminous proteins when 

 fed alone are inadequate for growth, although in this case appa- 

 rently the defect is not due to lack of necessary amino-acids, but 

 to some other undetermined cause. There are, however, many 

 single proteins which, when fed alone, seem to be entirely sufficient 

 to provide all the necessary nitrogenous material for maintenance 

 and growth. Such proteins are, for example, casein from milk, 

 edestin from hemp seed, glutein from wheat, lactalbumin from 

 milk, vitellin, etc. Experiments of this kind bring out in a decisive 

 way the important fundamental fact that proteins differ among 

 themselves in regard to their utility in furnishing material for cell 

 repair and growth, and the evidence at hand goes to show that the 

 quahtative differences are dependent upon variations in the amino- 

 acids of which they are composed. Zein is inadequate because 

 it is lacking in certain essential amino-acids, namely, tryptophan 



* Osborne and Mendel, "Carnegie Institution of Washington, Publication 

 156," parts I and II, 1911; also "Journal of Biological Chemistry," 12, 473, 

 1912; 13, 233, 1912, and 15, 311, 1913. 



