EFFECTS OF THIRST — ALBINO RATS 437 



Of the 41 rats listed, 11 were used for controls and the other 

 30 for the tests. The test rats were held at nearly constant body 

 weight for varying periods as follows: for about 1 week (3 fe- 

 males) ; 2 weeks (2 males, 1 female) ; 3 weeks (4 males, 2 females) ; 

 4 weeks (2 males) ; 5 weeks (2 males, 2 females) ; 6 weeks (1 male, 

 1 female); 7 weeks (1 male, 3 females); 8 weeks (1 female); 9 

 weeks (1 male, 2 females); 11 weeks (1 female); and 13 weeks 

 (1 female). Of the 30 test rats listed in table 1, one (K9.2 m.) 

 of the 9-weeks' group was omitted, on account of its large body 

 weight, from the corresponding group in table 2. 



Eight normal controls (3 males, 5 females) were killed at the 

 beginning of the experiment. The additional normal controls 

 (K5.2, K 5.3, K 8.5) were killed at the end of the time periods 

 indicated. These, and also two of the other controls (K7.1 and 

 K9.1) are not used in table 2, because their body weights are too 

 great for direct comparison with the test rats. A large number 

 of observations upon normal rats previously published by Don- 

 aldson, Hatai, Jackson, Lowrey, and others are also available for 

 comparison. 



During the experiment the rats were kept each in a separate 

 cage with wire-net bottom, allowing the feces and urine to drop 

 through, which might otherwise be eaten. Both feces and food 

 were carefully weighed. The rats were individually weighed 

 daily before feeding. Those under experiment were allowed dry 

 food ad libitum, together with whole milk carefully regulated in 

 amount so as to hold them nearly constant at the initial body 

 weight. Of course, slight fluctuations in the gross body weight 

 were unavoidable, but they rarely exceeded 2 grams above or 

 below the initial weight, as shown in table 1. The final gross 

 body weight is in all cases nearly the same as the initial weight. 



The temperature of the animal room was fairly constant at 

 about 75° Fahrenheit (extreme range 65° to 80°). 



Various methods of feeding were used. The eight initial con- 

 trols were killed shortly after weaning (which occurs at the age of 

 about three weeks), being subsequently fed on Graham bread 

 and whole milk. Two control rats (K5.2, K8.5) were fed with 

 dry 'dog-biscuit' (composition given by Kudo, '21) and water ad 



