FEEDING EXPERIMENTS WITH MICE 215 



their proper weight by gelatin feeding (chart 3). One mouse 

 Hved thus for fifty days. In no case did recovery of lost weight 

 occur unless at least two-thirds of the gelatin was replaced by 

 casein or some other 'adequate' protein. 



With zein as the only protein the decline was likewise continu- 

 ous but much slower, one-third the body weight being lost in 

 twenty-five days as compared with twelve days for mice fed 

 with gelatin. The appearance and behavior of the animals was 

 quite different; mice fed on the zein foods never exhibited the 

 wet-looking coat or the hunched up position, the excessive ac- 

 tivity or the ravenous appetite of the mice fed with gelatin. 

 When zein was replaced by casein, weight was regained fairly 

 rapidly; but the original weight was not quite reached by the 

 single mouse with which realimentation was attempted. A diet 

 in which half the protein was zein and the rest casein was appar- 

 ently satisfactory for maintenance; two mice, half-grown, throve 

 on it for a month, one making a substantial gain in weight. 

 The mice fed by Willcock and Hopkins on zein died before the 

 twelfth day; those fed with zein + tryptophane were alive and 

 active on the sixteenth day when the experiment was terminated, 

 but had lost weight. In my experiments mice fed with zein 

 lost on the average one-third of their weight in twenty-five days ; 

 while two mice which had an addition of tryptophane equal to 

 3 per cent of the zein fed lost only about one-fifth of their orig- 

 inal weight by the fiftieth day. 



There was no evidence of loss of appetite on either gelatin or 

 zein foods until the mice had lost so much weight as to be no 

 longer in normal health. That the character of the protein was 

 responsible for the failure became evident from the recovery that 

 promptly ensued when the diet was changed by substituting 

 casein for the inappropriate protein first fed. The inadequacy 

 of the gelatin or zein appears to be due to the inability of the 

 animal to synthesize one or more of the missing amino-acids; 

 for apparently improvement results from the addition of tryp- 

 tophane to the zein food. The success of Kauff mann^^ ^n^j of Ab- 



" Pfliiger's Archiv. Bd. 109, p. 440, 1905. 



