HOWARD M. LENHOFF 213 



poisoning the Hydra was shown in experiment 5 where the inhibited 

 animals from experiment 2 were washed and then immediately 

 placed in a fresh glutathione solution; these inhibited Hydra 

 responded again for an additional 29 minutes. These experiments 

 leave little doubt that reduced glutathione emitted from the prey 

 is the major natural substance activating the feeding reflex in Hydra 

 littoralis. 



EFFECT OF ENVIRONMENTAL CATIONS AND ANIONS 



As emphasized earlier, the Hydra's external aqueous environ- 

 ment takes on a special importance when studying the feeding 

 reflex. This fluid serves a dual role: it conveys glutathione from the 

 prey to Hydra, and it bathes both the receptor and the ecto- 

 dermal effector cells which are involved in part of the contractile 

 processes of the feeding reflex. Therefore, before directly investigat- 

 ing the mechanism by which glutathione activates the response, it is 

 necessary to consider the influence on the feeding reflex of the ions 

 in the media bathing the animals. Knowledge of the effects of these 

 ions might be useful in gaining insight into the mechanisms involved 



TABLE 4 

 Ionic requirements for the activation of the feeding reflex 



Hydra starved for one day used in all experiments. 



All ions were dissolved in a solution of 10-* M NaHCOs 



Data from reference 10. 



