226 MICROBES AND TOXINS 



these affinities as depending upon physical conditions, including 

 that of the electrical charges. 



The lipoid substances which are found in such abundance in 

 nerve-tissue and which constitute a constant component of 

 protoplasm, according to Overton furnish the cell with a sort 

 of envelope through which the food materials have to pass and 

 which behaves as a sort of colloidal atmosphere ; the principal 

 members of this group are lecithin and cholesterin. It is 

 inconceivable that they do not play some part in immunity 

 phenomena which are phenomena of nutrition. Haemolysin, 

 for example, undoubtedly induces changes in the lipoid coating 

 of the red blood corpuscles. 



The lipoid extracts of red corpuscles readily fix normal 

 hsemolysins, whereas the lipoid extracts of bacteria fix certain 

 immune-bodies. The lipoids also are capable of fixing the 

 complements. 



We have already mentioned two series of experiments in 

 which lipoids play a most definite part. In the first place we 

 have the activation of cobra venom by lecithin (Kyes), in which 

 the latter appears to play the part of complement. According 

 to Noguchi, triolein, oleic acid, exerts the same effect and loses 

 its activity quite like complement when heated. Oleic acid is 

 said to be capable of activating specific hsemolysins, and silicic 

 acid, which alone possesses a very feeble hsemolytic power, is 

 said to form with lecithin a complex or " lecithid " which is 

 much more powerful. 



In the second place lecithin plays the part of antitoxin 

 towards certain toxins. The bile or the soluble elements 

 of bile neutralize snake venom in appropriate dose ; the 

 cholesterin is the active constituent. Cholesterin and lecithin 

 neutralize the botulismus toxin. Cholesterin neutralizes 

 saponin, solanin, agaricin, vibriolysin, lecithids of cobra venom 

 and of the poison of bees : again it is its cholesterin content 

 which makes serum neutralize saponin. Finally in the 

 celebrated experiment of the fixation and neutralization of 

 tetanus toxin by the cerebral cortex (Wassermann and Takaki's 

 experiment) the lipoids of the grey matter are the active 



