RECEPTORS. 351 



the primary assumptions and show that the theory 

 continues to serve as an explanatory basis for 

 newly-discovered facts, and as a foundation on 

 which new researches may be instituted. 



In addition to the three main principles treated other impor- 

 tant Prin- 



oi above, the lollowing points are necessarily in- cipies of 



eluded in a summary of the views of Ehrlich, many 

 facts of a corroborative nature having been ascer- 

 tained in independent laboratories. 



1. The recognition of different types of tissue 

 receptors by which peculiarities in the action of the 

 different antibodies are explained. Eeceptors of 

 the first order, as antitoxins, anticomplements and 

 antiamboceptors, are regarded as relatively simple 

 bodies because no other constituent can be recog- 

 nized than the haptophorous group by which they 

 combine with their homologous substances. Ee- 

 ceptors of the second order are more complicated 

 in that they have something more than the mere 

 binding power; usually they are able to produce 

 some observable change in the substance with 

 which they unite. Hence, each has a toxophorous 

 or a zymotoxic group in addition to the hapto- 

 phorous, and the two groups are part of the same 

 molecule. Toxins, agglutinins, precipitins and 

 complements are receptors of the second order. 

 Receptors of the third order, i. e., the bacterio- 

 lytic, hemolytic and cytotoxic amboceptors, are 

 still more complex in that they are, so to say, only 

 partial antibodies, the complete body consisting of 

 the amboceptor-complement complex. The ambo- 

 ceptor is not an active body, but serves as an in- 

 termediary body to connect the active substance, 

 complement, with the cell. In the cytolytic proc- 



