I20 Immunity 



of alligators are insusceptible to the action of tetanus toxin, though 

 the haptophores of that toxin attach to the cells and occasion the 

 formation of tetanus antitoxin. 



All antitoxins and anti-enzymes may be accounted for as resulting 

 from the excessive regeneration of receptors of the first order and 

 their appearance in such of the body Juices as possess the antitoxic 

 or anti-enzymic quahty. 



II. Receptors of the Second Order (Agglutinins and Precipitins).— 

 It is assumed by Ehrhch that some of the . nutritive molecular 

 groups anchoring to the cells are not in condition to be utilized until 

 they have been subjected to preHminary treatment effected by 

 the receptor itself. To achieve this purpose another kind of recep- 

 tor, providing the means for such treatment, had to be imagined. 

 These are supposed to consist of two portions, one adapted to union 

 with the antigen (haptophore group) the other providing the means 

 of preliminary treatment (zymophore group). The appropriation 

 of the receptors by antigenic molecules of abnormal character being 

 of no benefit to the cells, new receptors of the second order are 

 regenerated in precisely the same manner as were those of the first 

 order, and similarly appear in the juices when their excessive num- 

 ber causes them to be thrust off from the cells. The quality imparted 

 to the serum by these haptines is, however, different from that 

 occasioned by haptines of the first order. The serum and juices 

 become agglutinating and precipitating, and in this group fall the 

 specific agglutinins and the specific precipitins. 



III . Receptors of the Third Order (Hemolysins, B acteriolysins, Cy to- 

 toxins).^ — ^When the antigen is still more complex it seems as though 

 the preparation for admission to the cell composition required other 

 substances than could be furnished by the cell itself, and must be 

 caught from the juices surrounding it. To meet this requirement, 

 Ehrlich conceived receptors with two adaptations — i.e., two separate 

 haptophore groups^ — one fitting to the molecular group to be 

 utilized, the other to some other molecular group (enzymic substance) 

 by which its utilization was to be made possible. In applying this 

 principle to the reactions of immunity, the antigen attaching to the 

 one side of the receptor, is brought into relation with the enzymic 

 substance called complement, attaching to the other end of the re- 

 ceptor, by the receptor itself, which then becomes the intermediate 

 body or amboceptor. Ehrlich was at first of the opinion that there 

 were as many different receptors of the third order — i.e., amboceptors 

 — as there were antigens, and that there was also a considerable 

 number of complements. It is now believed that he was correct 

 in the former assumption, but incorrect as to the latter, there being 

 but a single complement. 



The excessive regeneration and liberation of receptors of the third 

 order into the body juices is presupposed to occur just as in the case 

 of the receptors of the first and second order. These receptors or 



