156 THE BIOLOGY OF HYDRA : 1961 



genates (Table 3). This observation led to the realization that 

 Hydra extracts contain an inhibitor of this enzyme system (6). It 

 seemed reasonable to look for the inhibitor in the nematocysts, 

 since these structures could contain this substance and thus prevent 

 it from affecting the succinoxidase of the intact Hydra. 



TABLE 3 

 Demonstration of succinoxidase inhibitor in Hydra littoralis (from ref. 6) 



Tissue homogenate Succinoxidase activity 



^Qo2 = /A of O2 consumed per hour per mg. of tissue. 



*The extract was obtained from Hydra suspended in distilled water. The animals 



were disrupted in a 10 kc Raytheon sonic oscillator, and most of the nematocysts 



and nematocyst walls were removed by centrifugation. 



In all reaction vessels 0.1 ml. of a 5% homogenate of liver was used. 



A basic difficulty that has characterized nearly all of the studies 

 connected with coelenterate toxins has been the unavailabihty of 

 isolated, undischarged nematocysts. Most studies have been carried 

 out on toxic material obtained either from the whole animal or from 

 tentacles and acontia. At the time our study was performed we 

 also were unable to isolate clean, undischarged nematocysts. There- 

 fore, our evidence showing that we are dealing with nematocyst 

 material is indirect. Rather than to compare the amounts of in- 

 hibitory material in the various parts of Hydra, we attempted 

 to elicit nematocyst discharge from the live, intact animal and see 

 whether inhibitory activity is present in the culture Huid surrounding 

 the animals. Chemical compounds known to cause nematocyst 

 discharge were ineffective in our hands. Generally, the concentra- 

 tions needed to cause the response also caused great damage to the 

 animals. We did find, however, that a shock from a dry cell battery 

 would induce discharge without killing the animals and with con- 



