224 THE BIOLOGY OF HYDRA : 1961 



longer to open (Table 8). These results (Table 8) are interpreted 

 to mean that as the temperature is lowered, it takes longer for the 

 completion of all the reactions (including the limiting one) leading 

 to mouth opening.- 



TABLE 8 

 Effect of temperature on time of mouth opening 



Temperature 1 /t, 



(min. ) 



All Hydra were starved for two days. 

 Each value is the mean for 25 animals. 



ACTIVATION BY PROTEOLYTIC ENZYMES 



Recently we have been carrying out some experiments in acti- 

 vating the feeding response in the absence of added glutathione by 

 using certain proteolytic enzymes. Although still in the preliminary 

 stage, these experiments may help illucidate the sequence of events 

 taking place in the receptor-effector system, and thus are of sufficient 

 interest for some of them to be reported here. 



We have previously shown that papain, ficin, and trypsin acti- 

 vate a feeding response in Hydra (12). This proteolytic activation 

 was shown not to be the result of any toxic action of the enzymes 

 for the Hydra were intact and alive after one day's exposure to the 

 proteases. Dialyzed ficin, like papain (Table 9), did not activate 

 a response unless cysteine was added to render the enzyme active. 

 The boiled enzymes could not be activated by cysteine. The action 



-At temperatures below 13° Hydra vary greatly in their response, some animals not 

 responding at all. Therefore, the data are expressed as 1/tj rather than as tj because 

 in cases where there was no response, the t; values would range to infinity. 



