THE PHYSIOLOGICAL EVOLUTION, ETC. 381 



temperature intervals of 2 '5° or 4°. By making several 

 determinations with each animal, the average relation of 

 respiratory activity to temperature could thus be fixed with 

 a fair amount of accuracy. In the following table are given 

 the temperature intervals, both on warming and on cool- 

 ing, through which the carbonic acid output of the animals 

 remained practically constant. In those cases in which the 

 figures are placed in brackets the metabolism increased 

 or decreased with increase or decrease of temperature, but 

 to a much smaller extent than at temperatures above or 

 below the limits mentioned. 



In the case of the English frog, one series of determina- 

 tions showed the metabolism to remain practically constant 

 from 6° to 1 7*5° on gradually warming the animal, and to 

 diminish only slightly between 17-5° and 12-5° on gradually 

 cooling it. In another series, made three years later, the 

 carbonic acid output remained constant for a considerably 

 shorter interval on warming, but the rate of increase, with 

 increase of temperature, was very much less at temperatures 

 between 2 and 25°, than at temperatures above 25°. Of 

 all the nine animals examined, the newt, the toad, and, 

 strangely enough, the common earthworm, exhibited this 

 constancy of carbonic acid output to the most marked ex- 

 tent. Thus in all of these animals, it remained practically 



