EFFECT OF ANESTHETICS UPON LIVING PROTOPLASM. 315 



of experiments now in progress with Hydra. Every student of 

 zoology has watched this little animal contract on mechanical 

 stimulation. I have been able to show that when Hydra is anes- 

 thetized, so that it no longer responds to mechanical stimulation, 

 two types of anesthesia may be distinguished. In the one type, 

 the Hydra tends to contract its tentacles and to remain con- 

 tracted. This type of anesthesia is produced by ether and cold 

 and in general by those substances which lower the viscosity of 

 sea-urchin egg protoplasm. On the other hand, those substances 

 which increase protoplasmic viscosity tend to anesthetize the 

 Hydra in an expanded state. 



