ON SPECIFIC THERAPEUTICS. 17 



the union is merely a preliminary to their further 

 action on their prey. Thus one class of these 

 antibodies has the power of rendering the cells 

 assimilable by phagocytes (opsonins, bacterio- 

 tropic substances) ; another class (amboceptors) 

 has the power of rendering the cells liable to 

 the action of toxin-like constituents of the blood 

 serum (complements). In the latter case by 

 the simultaneous action of two substances a 

 destructive effect is produced. These sub- 

 stances are also called cytotoxins. For the 

 study of these the way has been prepared by 

 the work of Pfeiffer, Metchnikoff, and Bordet, 

 and by the discovery of Metchnikoff and 

 Bordet that haemolysins are produced by im- 

 munisation against blood corpuscles. 



These haemolysins are of special importance in 

 considering the question of the relations between 

 constitution, distribution, and action, because, 

 in their case, the haptophoric and toxophoric 

 groups are distinct, distribution and toxic 

 effect being dependent upon two different sub- 

 stances, the more stable amboceptor controlling 

 the distribution, and the labile complement 

 the toxic effect. The complement has no 

 direct relations with the cell, on which it acts 

 only through the medium of the amboceptor, 



c 



