HOWARD M. LENHOFF 



219 



HYDRA STARVED FOR TWO DAYS 



GLUTATHIONE CONCENTRATION (Molorify x 10") 



Fig. 3. Effect of glutathione concentration on the duration of the feeding 

 reflex. Each point represents the mean for five Hydra. The type of symbol 

 used indicates the number of Hydra in the group of five responding to 

 glutathione: i.e. o, five; •, four; [H, three; A/ fwo; and A/ one. (From 

 reference 8). 



excess glutathione is proportional to the number of active receptor- 

 effector systems in each Hydra. Thus, in order to get comparable 

 results, it is imperative in experiments using excess glutathione 

 concentrations (10^' M) that each Hydra possess approximately 

 the same number of such systems. Since it is impossible to know 

 beforehand the number of completed receptor-effector systems per 

 Hydra, the only criterion for obtaining quantitatively reproducible 

 results is to select Hydra reared under nearly identical laboratory 

 conditions. We repeatedly find that the standard deviation of the 

 response of Hydra to excess glutathione is lov^^ if these animals 

 come from the same mass culture (Table 1, expts. a-d). Therefore, 

 one should not compare experiments employing Hydra taken from 

 different mass cultures. Variation might result either from differ- 



