350 FRANCIS B. SUMNER 



these three mice seen, it is true, abnormally low, as will be realized 

 by inspecting the curve for this group as a whole, or by compar- 

 ing it with the other curves of the same series. 



The warm-room mice which were tansferred to the cold room 

 seem to have nearly or quite attained their power of heat regula- 

 tion at the age of sixteen days, though a small, constant differ- 

 ence is thereafter manifested between this group and those tested 

 in the warm room. • 



The very great variability shown even by mice of exactly the 

 same age is due in part to the size of the animals. Within each 

 expermiental group, I have compared, for each age, the smallest 

 and the largest individual, providing that the difference in weight 

 is as much as 0.5 gram or more. I find a mean temperature 

 difference of over 2° in favor of the heavier mice. But consider- 

 able differences are met with, even among mice of the same age 

 and size. 



Certain phenomena which were manifested during the death of 

 the young animals are of interest. In the warm I'oom, the maxi- 

 mum was not commonly reached until several minutes after the 

 fatal incision was made. In some cases, indeed, this maximum 

 temperature was manifested some time after the animal ceased 

 to move. Here is an example of a complete record for a 9-day 

 mouse : 



Mercury rose at once to 26 .5° 



After one-half minute 26 .9° 



After one minute 27 .2° 



After two minutes 28 .2° 



After three minutes 28 .6° 



After four minutes 28 .8° 



After five minutes 28 .6° 



After nine minutes 28 .0° 



It is recorded that this mouse ceased to move before the end 

 •of two minutes, except for one convulsive gasp, which was noticed 

 at the end of five minutes. 



In the cold room it likewise frequently happened that a rise of 

 temperature followed incision, so that the maximum was not 



