NUTRITION IN SENESCENCE AND REJUVENESCENCE 165 



completely acclimated to cyanide or alcohol, low temperature, 

 etc., than old, and acclimation occurs more readily at higher than 

 at lower temperatures (Child, 'n). In the low concentrations of 

 reagents used in the acclimation susceptibility method (pp. 82-84), 

 starved animals show very little capacity for acclimation as 

 compared with well-fed animals of the same size; in most cases even 

 less than large, old animals. In my earlier studies of suscepti- 

 bility only this acclimation method was used, and since in general 

 the capacity for acclimation had been found to vary with the rate 

 of metabolism, the very slight capacity of starved animals for 

 acclimation was regarded as indicating that their rate of metab- 

 olism was low. But the results obtained in later investigation 

 by the direct susceptibility method which have been briefly pre- 

 sented above, and the confirmation of these by the estimations of 

 carbon-dioxide production, force us to the conclusion that the 

 rate of metabolism increases during starvation. This being the 

 case, the decrease in capacity for acclimation in starved animals 

 cannot be due to a low rate of metabolism, but must be associated 

 with the nutritive condition in some way independent of meta- 

 bolic rate (Child, '14). When feeding is begun after a long period 

 of starvation, the capacity for acclimation rises almost at once 

 (Child, J u) and continues to increase as feeding continues and 

 growth replaces reduction. 



Since the nature of the process of acclimation is at present 

 unknown, this relation between nutritive condition and capacity 

 for acclimation cannot at present be analyzed, but must simply 

 be recorded as a fact. But whether acclimation results primarily 

 from a change in the metabolic substratum, or in the character 

 and relation of the metabolic reactions, the fact that the individual 

 with a supply of nutritive material from external sources has a 

 greater capacity for acclimation than the starving animal which 

 is undergoing reduction is at least suggestive, as indicating the 

 greater possibility of change under changed external conditions 

 in the well-fed animal. 



Whatever may be the nature of the relation between nutrition 

 and capacity for acclimation, the facts demonstrate that, although 

 the starved, reduced animals are practically identical with young, 



