DAVID L. CLAYBROOK 241 



DISCUSSION 



STREHLER: Do }'Ou need to include any particles along with 

 these soluble proteni fractions that were capable of supporting 

 growth? 



CLAYRROOK: Well, our solutions were centrifuged for six hours 

 at 33,000 g, which means that any sur\iving particles must have 

 been rather small. 



LENHOFF: I think what Dr. Strehler is getting at is that perhaps 

 the protein is being coagulated in the gut and is being engulfed as 

 particles. We have some evidence that H. littoralis gastrodermis 

 takes up mostly particles and leaves free amino acids behind in 

 the gut (Lenhoft, H. 1961. Exptl. Cell Research, 23: 335-353). Thus, 

 maybe the proteolytic enzymes destroy the growth-promoting prop- 

 erties of the heat-labile protein by reducing it to a non-particulate 

 solution of free amino acids that cannot be taken up by the gastro- 

 dermis. 



CLAYRROOK: We don't know what happens after it gets inside 

 the gut. 



GOREAU: What is Hydras digestive juice made out of? 



CLAYRROOK: I have no information on this. Do others? 



LENHOFF: We have fed about a million H. littoralis with shrimp, 

 until we knew, by other measurements, that the food was mostly 

 taken up by the gastroderm. Then we forced the Hydra to re- 

 gurgitate, took the extract, and precipitated it with 80% ammonium 

 sulfate. We found that there was proteolytic activity at pH 2.5 and 7. 

 These proteolytic enzymes probably aid in degrading the cells into 

 particles. But I doubt that the extracellular enzymes degrade the 

 particles all the way to free amino acids, because the particles, 

 when small enough, are rapidly phagocytized by the gastroderm. 



GOREAU: The reason I ask is that Claybrook's very lovely 

 method allows one to withdraw things as well as introduce them, 

 and I was wondering if one could do microchemical analyses on 

 contents of the gut of the animal during various stages of digestion? 



CLAYRROOK: I haven't tried this at all. I don't know. 



