IRRITABILITY 



IXFLUEXCE OF LIGHT 



log 



particular range of concentration within ivhich the organism is 

 sensitive. Above this range the fluid may injure, or even 

 destroy, the organism, whilst below this range there is no 

 reaction. These observations are in general agreement with 

 the results of similar tests on the effect of chemical substances 

 on spermatozoids, and small organisms. Molisch's results 

 are tabulated below. The organism used for experimentation 

 was Rho do spirillum giganteum. In the third column the 

 signs +, — , and O, have been inserted from Molisch's descrip- 

 tion, and were not so set down by the investigator himself. 



Irrit.ability and Environment. 



It was maintained by Kniep, who experimented with a 

 colourless sulphur organism and with Spirillum rubriini, 

 that the reaction of an organism to a particular salt is in- 

 fluenced by the presence of other salts. Thus Spirilhim 



14 



