IOO 



SENESCENCE AND REJUVENESCENCE 



length. The survival times are considerably longer than those in 

 Fig. 3 because of lower alkalinity of the water used. 



A marked difference in the susceptibility of the worms of differ- 

 ent size appears in the figure. The smallest worms (curve ab) 

 begin to die and disintegrate earlier and disintegrate more rapidly 

 than the others, and the susceptibility in the other lots decreases 

 as the size increases. In short, the larger worms possess a lower 



Stages . - 



V 



Hours 2! 3 i 4 i Si 6* 7i 8* 



FIG. 13. Susceptibility of Planaria dorotocephala to KCN o.ooi mol.: 



worms 5 mm. in length; ac, worms 7 mm. in length; ad, worms 10-12 mm. in length; 

 ef, worms 18-20 mm. in length. 



rate of metabolism than the smaller, and in general the rate of 

 metabolism decreases with increasing size. 



Hundreds of animals of this species have been compared in 

 this way, with cyanide, alcohol, ether, etc., as reagents, and the 

 result has been in all cases essentially the same. Tested by the 

 acclimation method, the smaller worms show a greater capacity 

 to acclimate to the reagent, i.e., a higher rate of metabolism, than 

 the larger, so that the results of the two methods check and confirm 

 each other. Moreover, the smaller animals grow more rapidly 

 than the larger under like conditions and are more active. 



