NUTRITION OSBORNE. 229 



months of such feeding most of the animals suddenly begin to decline and 

 soon die unless supplied with food. It has become evident from these inves- 

 tigations that the experimental food used during the first year of our work 

 was not suitable to meet all nutritive requirements of the animal. 



While these experiments were in progress control experiments were being 

 conducted with mixtures containing milk powder, since with this the 

 physical condition of the experimental foods could be closely imitated and 

 all the essential elements of a food of known value could also be supplied. 

 Animals on this food are still in fine physical condition after nearly two 

 years, have reproduced normally, and give every evidence that they can thus 

 be maintained under the experimental conditions throughout their natural 

 lifetime. 



As a result of this observation we have sought in the non-protein part of 

 the milk the essential elements lacking in the artificial food mixtures previ- 

 ously used. Accordingly the fat and protein were removed from the milk 

 and the residue obtained as a powder by evaporating to dryness. In order 

 to imitate the successful mixture containing the whole milk powder, we made 

 a food containing 28.2 per cent of the non-protein milk powder, 25 per cent 

 of pure lard, 23,8 per cent of starch, 5 per cent of agar, and 18 per cent 

 of one or another of the proteins to be tested. By using such foods we have 

 compared the nutritive effect of casein from cow's milk, edestin from hemp 

 seed, gliadin from wheat, glutenin from wheat, zein from maize, glycinin 

 from the soy-bean, ovalbumin from hen's egg, and lactalbumin from milk. 

 These proteins were chosen because they differ widely in their chemical 

 constitution. 



The foods containing each of the above-named proteins in the proportions 

 employed have thus far served equally well to meet the nutritive require- 

 ments of the mature rats, with the sole exception of the food which con- 

 tained zein. Although the rats ate a sufficient quantity of this zein food, 

 they constantly and rapidly declined in weight from the very beginning of 

 the experiment. Of the proteins thus tested, zein is the only one which on 

 hydrolysis yields no tryptophane, and it is highly probable that its failure to 

 maintain the animals was due to this deficiency. The chemical constitution 

 of tryptophane indicates that it is the source of several physiologically im- 

 portant constituents of the animal organism, and it is almost certain that 

 this amino-acid is essential for the maintenance of life. 



In respect to the question of synthesis of amino-acids by the animal 

 organism, our experiments have already afforded information which indi- 

 cates that such syntheses occur to a much greater extent than has formerly 

 been assumed. Thus, with the quantities used, casein which lacks glycocoU, 

 and gliadin which lacks glycocoll and lysine, have the same nutritive value 

 as those proteins which yield all the known products of protein decompo- 

 sition. The experiments conducted during the past year have established 

 beyond a question that, by the methods now employed, it is possible to con- 



