220 



THE BIOLOGY OF HYDRA : 1961 



ences in the following factors: the time elapsed since the previous 

 exposure to glutathione, the ratios of environmental cations or 

 anions, the temperature of the experiment, or to some presently 

 unidentified factors. 



EVIDENCE FOR AN INTRINSIC LIMIT 

 TO THE RESPONSE 



The data in Table 1 and Figure 3 show that the feeding reflex 

 is limited to 25-35 minutes, depending upon the conditions of the 

 experiments. In order to determine whether this mouth closure 

 resulted from some intrinsic change within the Hydra, or from the 

 oxidation or alteration of glutathione in the culture solution the 

 following experiment was performed: A group of 5 Hydra were 

 exposed to 2 ml. of 10~^ M glutathione until their mouths closed 

 (Table 6). The same glutathione solution was then transferred to 



AU Hydra were starved for one day. 

 Data from reference 8. 



another group of 5 Hydra; this latter group of Hydra opened their 

 mouths for 27 minutes, indicating that sufficient glutathione re- 

 mained to elicit a near-maximum response. This transfer process 

 was repeated, and again the Hijdra responded positively, although 

 for a somewhat shorter time. Using the p-mercuribenzoate proce- 



