84 



SENESCENCE AND REJUVENESCENCE 



old animals, but the young animals recover more rapidly and more 

 completely under the depressing conditions, and within a few days 

 are very evidently more active than the old. 



The relation between the capacity for acclimation and rate of 

 metabolism can be demonstrated very clearly by combining the 

 effect of depressing agents with that of different temperatures. 

 Animals in low concentration of cyanide or alcohol are less capable 

 of acclimation and die earlier at lower than at higher temperatures. 

 Fig. 5 shows the results in an experiment of this sort. The curves 



Fig. 5. — Planaria dorotocephala: death curves of full-grown animals in 1.5 

 per cent alcohol at 8°-io° C. {ah) and at 20° C. {ac). 



are plotted in the same way as in Fig. 4. The curve ab is the 

 death curve of forty animals in i^ per cent alcohol at a temperature 

 of 8°-io° C, the curve ac that of forty animals of the same size and 

 from the same stock in i| per cent alcohol at 20° C. The greater 

 resistance of the animals at the higher temperature is clearly 

 apparent. 



But that the rate of metabolism is not the only factor involved 

 in acclimation to depressing agents is evident from the comparison 

 of starved with well-fed animals. In experiments to be described 

 in following chapters it will be shown that in animals undergoing 



