1 8 CHESTER A. STEWART. 



Donaldson ('15) were of great value for comparison. In referring 

 to Donaldson's norm throughout the paper, comparison is always 

 made with the weight in animals of corresponding body length, 

 according to the method recommended by Donaldson ('15). 



Of the rats subjected to inanition, eighteen were held at nearly 

 constant body weight from three to twelve weeks of age, and 

 killed after being refed one half week (2 rats), one week (5 rats), 

 two weeks (5 rats), or four weeks (6 rats). In addition, two rats 

 of this series were killed at the end of the maintenance period 

 from three to twelve weeks of age. Thirteen rats were refed 

 until adult (about I year old) after being held at constant body 

 weight for various periods : from the age of three weeks to age of 

 four weeks (4 rats), from three to six weeks (4 rats), and from 

 three to ten weeks (5 rats). The test rats of litters 823 and 824 

 were held repeatedly at constant body weight for short periods 

 during the first two or three months, and during the intervening 

 times were amply fed. Later a different plan was adopted, the 

 rats of these two litters being alternately severely starved and 

 refed. 



The rats were kept in ordinary wire cages provied with wire 

 net bottoms, which permitted feces and other waste materials 

 to drop into the box base below. It is necessary to use this type 

 of cage to prevent the underfed rats from eating their feces. 

 The cages were kept as clean as possible, and the rats remained 

 healthy with the exception of some lung infection, especially 

 among the older rats. 



The temperature of the room in which the control rats were 

 kept remained usually at about 21 C. (70 F.), but occasionally 

 it dropped as low as 16 C. (56 F.). Inasmuch as underfed 

 rats are very susceptible to cold (even a slight chilling being 

 sometimes fatal), a part of them, litters Stio, Stu, Sti2, were 

 kept in a separate room where the temperature ranged con- 

 stantly between 27 and 32 C. (80 and 90 F.). The reduced 

 power of the underfed rats to resist cold is probably due to the 

 exhaustion of reserve material in the body, which ordinarily 

 would be oxidized to maintain the normal temperature. 



In spite of keeping the test rats very warm, it was found very 

 difficult to hold them strictly at constant body weight for more 



