HOWARD M. LENHOFF 



223 



and information concerning its role in the execution of the response. 

 These experiments are still in the notebook stage and will be sum- 

 marized here only in order to show you some of the directions our 

 research is taking. 



If the reactions of the feeding reflex (Fig. 5) are depicted as in- 

 x'olving the conversion of limiting substance X to Y, then one might 

 expect two major results of lowering the temperature. First, a small 

 lowering in temperature should lower the rate of all the thermo- 

 chemical reactions. However, by slowing down the reaction con- 

 verting the X to Y we should therefore slow down the rate at which 

 the supply of X is depleted, and thus increase the length of time 

 that the mouth remains opened. This proved to be the case as shown 

 in Table 7 where, as the temperature approaches 15 \ the Hi/dm 

 respond for nearly 100 minutes. 



TABLE 7 

 Effect of temperature on the duration of the feeding reflex 



All Hydra were starved for two da) s. 



As a second efl^ect of lowering temperature, the limiting reaction 

 may go so slowly that the optimum (threshold) conditions neces- 

 sary for the feeding reflex are not maintained. Thus, when the 

 Hydra are held below 15° they are observed to open their mouths 

 for a few minutes, then close, open, etc. until they finally stop 

 responding. The total duration of the responses below 15 becomes 

 progressively less until the Hydra barely respond (Table 7). In fact, 

 when the temperature is lowered from 20" to 5", the mouth takes 



