FEEDING EXPlfelMENTS WITH MICE 213 



During the time that the experiments lasted all the proteins 

 used and enumerated above, except gelatin and zein, seemed to 

 be interchangeable in so far as maintenance is concerned. Casein 

 was fed as the sole protein for six months; lactalbumin, glutenin, 

 gliadin, and edestin each for shorter periods varying from one 

 to five months. Half-grown or still smaller mice did not grow 

 on these foods nearly so fast as the control animals grew on a 

 mixed diet (i.e., the foods, while entirely adequate for main- 

 tenance, were inadequate for growth); but the animals were 

 still active, sleek, apparently well, with no decline in weight at 

 the end of four, five and six months, and some had made consid- 

 erable gains in weight — 130 per cent in the case of one mouse 

 on casein food. During this time hemoglobin and other blood 

 proteins, ©lastin, collagen, the keratin of the skin, and hair, and 

 so forth, must have been manufactured from a single protein 

 of widely diiTerent composition from these or from its cleavage 

 products. With casein a synthesis of glycocoll must be assumed; 

 if the phosphorus-free edestin is the source of nitrogen, the 

 organism's supply of complex phosphoi-us compounds, nucleopro- 

 teins, phosphatids, and so forth, must be synthesized, with only 

 the phosphoru compounds of the protein-free milk as raw mate- 

 rial. Gelatin and zein, however, are not equal to the other pro- 

 teins used, perhaps because the body is not able to manufacture 

 one or more of the amino-acid groups missing from them. When- 

 either of the two was fed as the only protein, decline in weight 

 began at once and other evidences of ill health appeared. 



All the animals living on gelatin as the sole protein became 

 very restless and acquired a characteristic peculiar appearance; 

 they were emaciated, the rump was flattened, the hind legs 

 drawn up under the body and the coats rough, as though they 

 had fallen into water and partly dried. If one-fourth of the gel- 

 atin was replaced by casein, the roughness disappeared and the 

 decline stopped, but no recovery of lost weight took place; that 

 is, for a time there was maintenance, without repair, on a diet in 

 which three-fourths of the protein was in the form of gelatin. 

 Both on this food and on a similar one in which one-third of 

 the gelatin was replaced by casein, the body weight after a 



