204 THE BIOLOGY OF HYDRA : 1961 



them so remarkably adaptable to quantitative study is their lack 

 of a definite self-regulated internal extra-cellular fluid. In place 

 of this fluid is their culture solution, a solution regulated by 

 the investigator. Once the environment is controlled, individual 

 variation between hydra is minimized and thus the results are 

 rendered less ambiguous. 



Working on the assumption that the intact Hydra can be treated 

 with the same controlled conditions that we normally employ with 

 an enzyme in solution, we find that in order to get reliable results 

 with the glutathione-//j/f/rfl system, we must control precisely and 

 within restricted limits the following factors, some of which I will 

 report on today: pH, nature of the buffer, ionic strength, the nature 

 of both the cations and anions, temperature, presence of trace 

 metals, amount of aeration, concentration of glutathione or related 

 compounds, presence or absence of proteases or glutamic acid, and 

 length of time since previous exposure to glutathione or since last 

 feeding. Undoubtedly, there are other factors that are as yet 

 unknown. 



Of course, when studying developmental phenomena, more com- 

 plex problems are met with. At present such phenomena as regen- 

 eration, budding, and cell migration have none of the convenient 

 environmental chemical "handles" (comparable to glutathione and 

 pCOo) which have so often provided the means of attacking a 

 problem. Yet certainly many of the environmental factors aflFecting 

 the feeding reflex also influence developmental phenomena. For 

 example. Hydra grown in a culture solution low in sodium have 

 smooth short tentacles and few nematocysts. At even lower sodium 

 concentrations the ectoderm thickens, developmental abnormalities 

 occur, and often cellular areas begin to disintegrate. These abnor- 

 malities never occur in a medium of the proper sodium content ( 11 ). 



Research with a whole animal challenges the quantitative biol- 

 ogist. When he treats hydra with the same precision that he treats 

 an in vitro system, he will find that much of the mystery surround- 

 ing the animal disappears and that the excitement of a new under- 

 standing beckons. 



Now let us consider the activation of the feeding reflex in 

 Hydra littoralis by the tripeptide reduced glutathione. We owe 



