354 FRANCIS B. SUMNER 



3. Young mice of the same age differed greatly in their power 

 of heat regulation. The extent of this power depended partly 

 upon the weight of the young animals, heavier individuals show- 

 ing a higher degree of regulation. 



Berkeley, California 

 May 14. 1913/ 



SUPPLEMENTARY NOTE 



Opportunity has very recently been afforded me to repeat 

 certain of the experiments described in the preceding pages, and 

 the results seem important enough to make it desirable for me to 

 include them in the present paper. These supplementary experi- 

 ments were conducted at the University of California, between 

 August 31 and September 16, 1913. For the loan of some of 

 his mice, as well as for the privilege of using his animal room, I 

 am indebted to Dr. J. A. Long, of the Zoology Department of 

 the University. My thanks are also due to Dr. J. F. Mitchell, 

 of the Veterinary Department, for the privilege of keeping the 

 mice for a number of days in the cold-storage room of the hog- 

 serum laboratory. 



Five male white mice, averaging 24.5 grams in weight, and 

 five females, averaging 21.4 grams were used. These mice were 

 probably all between five and ten months old. 



The temperatures of the animals were first taken throughout 

 a period of seven days, in the attic room in which they had been 

 reared. For at least a month prior to my experiments, the tem- 

 perature of this room had ranged between 20 and 26°C. 



The methods employed were the same as those described for 

 my earlier experiments. The figures here given are in all cases 

 30-second ones. The tests were made, for the most part, in the 

 forenoon. Readings have been rejected which were affected by 

 the struggles of the animal or by any other known disturbing 

 influence. 



In the attic room (mean air temperature, 21.5°; relative hu- 

 midity probably 40 to 60 per cent, most of the time), 22 tests of 

 five males, on six different days, gave a mean body temperature of 



