HOWARD M. LENHOFF 207 



starving for one or two days mass cultures of Hydra Uttoralis (18) 

 that had been reproducing asexually in a sokition consisting of 10~^ 

 M CaCL and 10~^ M NaHCO;; in deionized water. Special care was 

 taken to remove most of the organic waste products from the cul- 

 tures twice daily (18). The animals in each tray were not allowed 

 to reach a density of over two or three thousand hydranths per 1500 

 ml. of culture solution. 



The assay procedure used in most of these experiments was as 

 follows: Five starved Hydra obtained from the mass cultures were 

 rinsed three times in 30 ml. portions of a solution lacking gluta- 

 thione and consisting of 10"-^ M CaCl,, 10"^ A/ NaCl, and 

 10~^ M histidine chloride buffer, pH 6.2. The fixe Hydra were then 

 transferred in one drop of the solution into 2 ml. of the same solu- 

 tion containing glutathione (Sigma, St. Louis, Mo.). (Reduced 

 glutathione is not readily oxidizable at pH 6.2.) This glutathione 

 solution was in the spherical concavity (36 mm. diam. x 5 mm. deep) 

 of a Maximov tissue culture slide. The Hydra were immediately 

 observed through a binocular dissecting microscope set at a magni- 

 fication of 19.5. The time intervals between the moment the Hydra 

 were placed in the glutathione solution and the initial and final 

 (ti and tf) times that the mouth of each animal was open were 

 recorded. The magnitude of the feeding reflex is expressed as the 

 average time (tf-ti) during which the mouths of the Hydra remained 

 open in response to glutathione. 



In Table 1 are shown the results of four different experiments 

 (a-d) which were carried out in excess glutathione. In these experi- 

 ments each Hydra opened its mouth within 0.4 to 1.0 minutes (ti) 

 after being placed in the glutathione solution. Under optimal con- 

 ditions, the variations observed in the opening time ti were small 

 when compared to tf, and did not significantly alter the o\'erall 

 time during which the mouth was open (tf-ti). 



The closing time (tf) for the individual Hydra in each experi- 

 ment (Table 1, expts. a through d) was about 35 minutes. Because 

 the standard deviations were small in comparison to the total length 

 of the response, they were not routinely calculated. 



At sub-optimal concentrations of glutathione (Table 1, expt. e), 

 or in the presence of a compound known to compete with gluta- 



