206 



THE BIOLOGY OF HYDRA : 1961 



A B C 



Fig. 1. Stages of the feeding reflex (see text) (From Ref. 8). 



A QUANTITATIVE ASSAY 



Requisite for quantitative studies of any biological phenomenon 

 are accurate and reliable measurements. Therefore, special empha- 

 sis is placed on the assay procedure which has as its basis the visual 

 measurement of the mechanical process of mouth opening. 



Meaningful measurements of the feeding reflex require Hydra 

 that respond to glutathione in a quantitatively reproducible manner. 

 Large numbers of such experimental animals were obtained by 



