GENERAL CHARACTERS OF LIVING ORGANISMS 47 



materials present in the surroundings, the existence of a 

 highly developed responsiveness to the external chemical 

 conditions is to be expected. It is especially remarkable 

 that certain groups of compounds — the lipoid-solvent or 

 anaesthetizing group — have a similar reversible depres- 

 sant action on protoplasmic activities in all organisms, 

 from bacteria to higher plants and animals. 



We may class therefore as universal properties of 

 protoplasm: (i) electrical sensitivity, and (2) sensitivity 

 to the presence of special chemical substances in the 

 surroundings. In studying the problem of the conditions 

 of stimulation we are thus brought to consider more 

 especially the reactions of living matter to electricity 

 and to chemical substances in the environment. The 

 fundamental or essential features of protoplasmic 

 structure and composition must be those which determine 

 the special responsiveness to influences of these two 

 kinds. 



