W. F. LOOMIS 361 



medium, the Hydra die for the pH becomes too acid. I do not 

 have the full answer yet about just how much alkalinity, increased 

 pCO., and the bicarbonate ion matters. Probably all three do, at 

 least indirectly through the Henderson-Hasselbalch equation, but 

 also perhaps each directly in its own right. An additional complica- 

 tion lies in the fact that crowded Hydra liberate ammonium bicar- 

 bonate in significant amounts and this salt can substitute for sodium 

 bicarbonate as a pH buffer. 



Now you asked about the pCOs-bicarbonate equilibrium. Well, 

 aerated bicarbonate-Versene-calcium solution does not work, hence 

 the bicarbonate alone is not enough. What is needed in addition 

 it seems is the CO:, that comes from the respiration of crowded 

 Hydra. 

 KLINE: Will there always be an equilibrium between the two? 



LOOMIS: Yes, a three-way equilibrium between pH, pCOo, and 

 bicarbonate. You can set each one in an experiment and hold it 

 constant while you vary the other two reciprocally, and you can do 

 this for each of the three variables in turn. In this way, you can 

 determine the role of each variable independently. I hope to do 

 this as soon as I have the "halo zone" under control. The final 

 answer will come when a solution can be prepared that will turn 

 isolated single Hydra sexual without the need for any crowding 

 or stagnation. 



LENHOFF: I would like to propose a mechanism showing one 

 way in which CO^. can play a role in controlling sexual differentia- 

 tion. This \iew emphasizes that COo is an important metabolite 

 needed for synthetic processes of the cell. First we must recognize 

 that aside from producing CO. the Krebs cycle also serves at 

 least two other major functions; it provides hydrogen atoms for 

 energy production; and, of equal importance, it provides carbon 

 skeletons for the synthesis of major portions of other molecules, 

 such as some unessential amino acids and pyrimidines. Thus, when 

 unusual demands are put on the cell's synthetic machinery, such as 

 occurs during cellular differentiation, the keto acids may be pulled 

 out of the Krebs cycle to give, for example, amino acids for protein 

 synthesis. That is, «-ketoglutarate and oxaloacetate yield glutamate 

 and aspartate on amination. When under these demands, the cell 



