222 THE BIOLOGY OF HYDRA : 1961 



40 I- 



10 20 30 40 



HOURS AFTER INITIAL EXPOSURE TO 6SH 



Fig. 4. Time for recovery of the ability to respond to glutathione (see 

 text). 



during the first hour, the animals give Httle if any response. By the 

 tenth hour, however, the Hydra had regained their abihty to respond 

 for about 15 minutes, and after one day, responded maximally. 

 Extending the interval between exposures to o\'er 70 hours did not 

 result in any further increase in the length of their response to fresh 

 glutathione. 



This lag and gradual resumption in the ability of Hydra to 

 respond to a fresh stimulus of glutathione is interpreted to signify 

 the period for the resynthesis of some substance, called "X," which 

 we postulate to be limiting in the receptor-effector system. This 

 view places a greater emphasis on the state of the receptor-effector 

 system than on the physiology of the whole animal. 



EFFECTS OF TEMPERATURE 



The effects of temperature on the feeding response were studied 

 primarily to provide more evidence concerning limiting substance X 



