Trichocysts and Nematocysts 



657 



cases produce serious illness or even death. The nature of the toxin associ- 

 ated with nematocvsts is largely unknown. Various toxic fractions have been 

 prepared from nematocyst-containing tissues.-- ^ 



The cnidoblasts respond as independent effectors in the discharge of their 

 nematocysts. There is no evidence of control of these by any coordinatory 

 mechanism within the organism. In their normal responses, and in response 

 to highly localized electrical stimuli, there is a complete restriction of the 



"^^, 



Fig. 249. Discharge of nematocysts of Anemonia to various stimuli, a, Touch by a 

 human hair, h, Touch by a clear, blunt glass rod fails to cause discharge, c, Response 

 to clean glass rod after sensitization of the cnidoblasts with dilute saliva extract, d, 

 Response to glass rod smeared with alcohol extract of Pecten gill. From Pantin.^" 



discharge to the specific region excited. ^^' ^* Intense mechanical stimulation 

 by inert objects will induce only a weak discharge, whereas mild mechanical 

 stimulation by natural foods is sufficient to evoke a strong response (Fig. 

 249). Submersion of cnidoblasts in a weak extract of a normal food which 

 will typically not itself induce discharge will greatlv lower the threshold of 

 these effectors in Anemonia to purely mechanical stimuli. ^^ The specific food 

 factors that are involved in this sensitization are lipoidal substances adsorbed 

 upon proteins. The adsorptive forces are so strong that the factors cannot 

 be removed by ether extraction, but thev can be with alcohol. The active 

 chemical substances appear to have properties resembling sterols and phos- 

 pholipins and to be highly surface-active. In view of the rapid and thorough 

 discharge of nematocysts even to dried foods, it would appear that the nor- 

 mal reaction must be "contact-chemical" in character, chemical sensitization 

 to mechanical stimulation occurring almost instantaneously. 



