IMMUNITY 225 



to those of colloids. In any case, there might exist between 

 the antibodies and antigens on the one hand, and the colloids 

 on the other, considerable differences without preventing the 

 general laws of attraction and adsorption from being equally 

 applicable to the former as to the latter. 



Agglutination and precipitation closely resemble the flocking 

 of colloids. Bacteria behave towards a precipitating serum in 

 the same way as they behave to certain substances quite 

 foreign to the body, such as gelatine or gum-arabic. 



Bacteria, in presence of a solution of ferric chloride, are 

 protected by the colloidal ferric hydrate from agglutination by 

 their specific agglutinin. 



The phenomena of specific haemolysis (i.e., haemolysis by 

 the serum of immunized animals) have been imitated 

 by attacking the corpuscles by means of such systems as 

 silicic acid + lecithin, colloidal ferric hydrate + dog- 

 serum, or saponin + taurocholate of sodium : the two kinds 

 of phenomena may be expressed by the same curves 

 (Zangger, Mile. Cernovodeanu, and V. Henri). Comple- 

 ment can be fixed by the most diverse substances, by 

 Witte peptone, yeast cells, the cells of organs, and various 

 precipitates. 



The toxin + antitoxin reaction has been " imitated " by the 

 interaction of arsenious acid and colloidal ferric hydrate. The 

 phenomenon of Danysz-Dungern can also be reproduced with 

 colloids ; the final result in the precipitation of a colloidal 

 suspension is different according as the precipitant is added in 

 one large or in fractional doses. 



The reactions between cholesterin and various poisons and 

 between cholesterin and lecithin have the appearance of 

 colloidal reactions. One may even observe affinities of the 

 character of the specific affinities. For example, cholesterin 

 neutralizes saponin and tetanolysin, but has no effect on ricin 

 or staphylolysin. Complement is absorbed, as has been seen, 

 by a great variety of substances ; agglutinin, however, possesses 

 affinity chiefly for the colloidal protein, while tetanus toxin is 

 chiefly fixed by the lipoids. It is legitimate to conceive of 



Q 



