354 



THE BIOLOGY OF HYDRA : 1961 



pCOa in % Atm 

 on Log Scale 

 5.00 

 4.00 



3.00 

 2.00 



1.00 



.50 

 .40 



.30 

 .20 



.10 



.05 



7.0 



7.2 



7.4 



7.6 



7.8 



8.0 



82 



PH 



Fig. 6. Logarithmic calibration curves relating pH and pCO., in two solu- 

 tions (25 ): (1) 2 10 • M NaHCO,; 5 10"^ M CaCL„"and (2) BVT 

 solution prepared as described in Loomis and Lenhoff (21). Values of pC02 

 obtained by method of Loomis (17). 



cycle of alternating high and low levels of pCOo is required for 

 differentiation to occur. 



Before concluding this presentation, I would like to broaden the 

 discussion by suggesting that pH, pO., pNH,. and pCO. affect 

 many biological systems other than Hydra. Some of these systems 

 have been mentioned in previous publications (14, 16, 18), but 

 preliminary experimental work in this laboratory suggests that the 

 following phenomena are controlled by one or more of these four 

 feedback variables : 



1. Tentacle number and rate of bud growth in Hydra (20). 



