PROPERTIES OF ANTISENSITIZERS. 305 



cilable. Why is not the law that controls these phenomena more 

 general? 



To explain the contradictory facts in harmony with Ehrlich's 

 theory the following explanation has been offered: Diphtheria 

 antitoxin and typhoid agglutinins have affinity for only such 

 receptors as occur in their respective micro-organisms. It is natural, 

 then, that these substances should remain free in the injected animal, 

 since they find no appropriate receptors; as these receptors are 

 lacking, they are not reproduced and consequently no active anti- 

 serum is formed. It might be objected that if this explanation 

 were true that Pfeiffer and Fried berger would have obtained no 

 antisensitizer to cholera serum. But this objection could, in turn, 

 be answered by saying that although the injected animal' has no 

 receptors identical with those of typhoid or diphtheria bacilli 

 and consequently fitted to fix the active substances that affect 

 these organisms, they do possess receptors similar to those of the 

 cholera vibrio. If the experiment had turned out the other way, 

 that is to say, if an antityphoid serum had been obtained more 

 easily than an anticholera serum, the converse explanation of the 

 respective absence or presence of receptors could have been offered. 

 In short, whether an antiserum is obtained or not, the receptor 

 theory is upheld; in unfavorable cases receptors are lacking; in 

 favorable cases they are present. Whatever happens, the use of 

 the term "receptors" makes the facts easily explicable. 



Another explanation of these divergent results may, however, be 

 offered. As we have already seen, the serum of a guinea-pig im- 

 munized against rabbit serum neutralizes the various specific 

 sensitizers from the rabbit indifferently, and also the normal sen- 

 sitizers (or substances of this nature) in normal rabbit serum. And, 

 what is more, a single given antisensitizer confers all these antagonis- 

 tic powers on the antiserum or is able, in other words, to show these 

 various affinities by uniting with the various sensitizers. 



It follows, therefore, that to neutralize a given specific sensitizer 

 (e.g., rabbit > ox sensitizer) economically by means of an anti- 

 serum it is well to have the sensitizer in a relatively pure condition, 

 without admixture of other sensitizers, before treating it with- the 

 antiserum. Under these conditions the neutralizing effect of 

 the antiserum is directed only against the sensitizer in question. 



