FEEDING EXPiJRiMENTS WITH MICE 211 



Long continued constancy of body weight was used as the chief 

 criterion of the adequacy of a ration for maintenance, although 

 general appearance and behavior were found to be surprisingly 

 indicative of health or of malnutrition. Mice kept on diets 

 which ultimately proved inadequate were either sluggish and 

 stiff in their movements or extremely restless, constantly run- 

 ning around their cage almost like dancers ; and their coats quickly 

 acquired a very noticeable roughness. On the other hand, mice 

 on diets which prolonged feeding showed to be adequate were 

 active without restlessness, had sleek, smooth coats, and in 

 general could not be distinguished from the control animals on 

 a mixed diet of dog biscuit, sunflower seeds, meat and carrots. 



On a food paste consisting of a single protein, fat, carbohy- 

 drate and the 'protein-free milk' first employed by Osborne and 

 Mendel with rats, mice were kept alive and apparently in ex- 

 cellent health for six months, a quarter of their normal life-time. 

 At the end of that period the experiment had to be terminated 

 owing to my departure from New Haven; but there was no 

 evidence that these mice could not have lived for a longer time 

 without change of diet. Different proteins, including the animal 

 proteins casein, lactalbumin, and gelatin, and vegetable proteins 

 glutenin, gliadin, edestin, and zein were fed for periods of from 

 one to six months. 



Because of the importance of mere traces of various ions, es- 

 pecially in animals as small as mice, a suitable salt mixture is 

 difficult to find. As was found by Osborne and Mendel with 

 rats, in every case a steady loss of weight and ultimate death 

 followed the feeding of foods containing the inorganic salts in 

 the form of Rohmann's mixture^" if a change in the diet was not 



1° Ca3(P04)2 10 grams 



K2HPO4 37 grams 



NaCl 20 grams 



Na citrate 15 grams 



Mg citrate. 8 grams 



Fe citrate 2 grams 



Ca lactate 8 grams 



From Osborne and Mendel: Carnegie Institution of Washington, Publica- 

 tion 156, Part I, p. 32, 1911. 



