HOWARD M. LENHOFF 231 



able amounts of all kinds of organic substances which activate 

 chemoreceptors to trigger the corals' feeding posture. Corals feed 

 any time there is plankton around. The classic story that reef corals 

 expand only at night is untrue. In fact, we have frequently seen 

 corals feeding on swarms of zooplankton in the middle of the day 

 irrespective of light intensity, using tentacles and extruded mesen- 

 terial filaments to catch and entangle their prey. 



LENHOFF: It would he nice to see whether methionine analogs 

 will inhibit this response in corals elicited by clam juice. This would 

 provide strong evidence that methionine is the actixe compound 

 in the clam juice. 



STREHLER: Langdon found that the reduced chain of insulin 

 is a competitive inhil:)itor of glutathione-TPN reductase. Have you 

 tried reduced insulin? 



LENHOFF: We have not tried insulin or reduced insulin yet. But 

 Langdon's finding places this experiment high on our list. 



Another point I find exciting is that Langdon calls insulin a 

 "prohormone." That is, he suggests that insulin will not work unless 

 it is first split, although here it is split by reduction. Thus, insulin 

 may represent a case of an excitatory compound being activated 

 by the unmasking of an essential group. We think that unmasking 

 phenomena (possibly proteolytic) may operate in control systems 

 generally. 



BURNETT: Did you repeat the experiments of Balke and Steiner 

 showing that lactic and ascorbic acids elicited a feeding reflex? 



LENHOFF: Yes. I found neither lactic nor ascorbic acid to work. 

 However, I still wouldn't be surprised if under certain conditions 

 other compounds also activate. For example, they may act, like 

 the proteases, along the chain of reactions involved in the feeding 

 reflex. Perhaps lactic acid, under their conditions affected some 

 step of the response. And there still remains the possibility that 

 Hydra has more than one receptor. All I can say is that in Hydra 

 littoralis all the factors that I mentioned in my talk influence the 

 response, and that there is no question that reduced glutathione is 

 a natural activator. 



