212 THE BIOLOGY OF HYDRA : 1961 



of this remarkable specificity and of the ample glutathione in the 

 fluids emitted from Hydra s captured prey in nature, the possibility 

 remained that some unknown trace factors present in these fluids 

 are the natural activators of the feeding reflex. 



To examine this possibility, the following series of experiments 

 were carried out ( Table 3 ) : a diluted aqueous extract ( 30;iig. ) 

 from homogenized Arfemia elicited a 37 minute feeding response 

 in Hydra (expt. 1). A similar extract containing 10~^ M added 

 glutamic acid gave only a 7 minute response (expt. 2). The glu- 

 tamic acid was presumably competitively inhibiting the glutathione 

 in the Artcmia extract because, if in addition to 10~^ M glutamic 

 acid, 10~"' M glutathione, was also included, then the inhibition 

 was reversed ( expt. 3 ) . The inhibition was also reversed by increas- 

 ing the amount of shrimp extract (expt. 4). Further evidence that 

 the glutamic acid was acting competitively and was not irreversibly 



TABLE 3 



The inhibition by glutamic acid of the feeding reflex induced by Artemia 

 extracts, and the reversal of that inhibition by glutathione 



Expt. Test Solution tj-t; 



( mill. ) 



1. 30 p,g. Artemia extract. 37.3 



2. 30 fig. Artemia extract and 



10^ M glutamic acid. 7.4 



3. 30 /ig. Artemia extract, 

 10~* M glutamic acid, and 



10"^ M reduced glutathione. 40.6 



4. 140 ng. Artemia extract and 



10-' M glutamic acid. 26.5 



5. Hydra from expt. 2 in 



10"" M reduced glutathione. 29.1 



6. 10-" M reduced glutathione 42.1 



Hydra starved for two days were used in all experiments. 



