1 88 PROTOPLASMIC ACTION AND NERVOUS ACTION 



structural substratum of protoplasm in a manner which 

 does not permanently change its properties or physical 

 state. Hence in their presence physiological processes 

 are modified temporarily in rate or character, and resume 

 their former conditions when the substance is removed. 

 The special affinity of these compounds for substances 

 having fat-like properties indicates that their primary 

 action is on the lipoid constituents of protoplasm; their 

 possible action on proteins, however, is also to be consid- 

 ered. In general they include the substances comprised 

 in Overton's first group (alcohols, ethers, esters, normal 

 and substituted hydrocarbons, etc.). 



We distinguish, therefore, two chief groups of com- 

 pounds which by means of their reversible influence on 

 the structural substratum of protoplasm may modify 

 vital processes without affecting them permanently or 

 injuriously: (a) neutral salts or other electrolytes 

 (acid and alkali), and (b) lipoid-solvent or surface-active 

 organic compounds. These two groups may be charac- 

 terized respectively as general colloid-alterants and 

 lipoid-alterants. The compounds of these groups differ 

 somewhat sharply in their physiological action from those 

 compounds whose chemical effects tend to be irreversible; 

 the latter include most of the strong oxidizing and reduc- 

 ing agents and the salts of heavy metals; usually these 

 are not capable of modifying physiological processes with- 

 out permanent injury; hence they are toxic or poisonous 

 in small doses. Recovery from the effects of this ' ' poison- 

 ous" group depends upon the reparative activity of 

 the living protoplasm, just as does recovery from mechan- 

 ical injury, and not upon a simple reversal of the chemical 

 or other action of the compound. 



