UNION OF IMMUNE-BODY 11 



were added to the standard amount of red cor- 

 puscles. 



1 free dose of IB was obtained when 12 doses of IB were added 



2 free doses of IB were 16 



3 ,, ,, 20 

 * > > && > > 



It is accordingly not possible to state exactly how much 

 immune-body can be taken up by the red corpuscles, as 

 the amount entering into combination varies with the total 

 amount present ; the condition being, in this respect at 

 least, analogous to mass action. In any case, however, 

 the combining powers may be suitably indicated for com- 

 parative purposes by stating the minimum number of doses 

 which will leave one dose free. This, however, is only a 

 conventional standard. 



In the combination of immune-body with red corpuscles 

 (anti-substance with antigen) we have an exaggerated 

 example of what is now known as the ' Ehrlich Pheno- 

 menon'. In studying the union of toxin and anti-toxin, 

 Ehrlich found that if he ascertained the largest amount of 

 toxin which was just neutralized by a unit of anti-toxin, 

 this amount had to be increased by much more than one 

 lethal dose before the mixture became lethal to the test 

 animal. He explained this result by the complicated con- 

 stitution of the toxin, and especially by the presence of 

 toxoids which have a weaker affinity for the anti-toxin 

 than the true toxin has. He also considered that the union 

 of toxin and anti-toxin is of firm character; that is, it is not 

 reversible. In the present case, namely, that of immune- 

 body and red corpuscles, it can be readily shown, however, 

 that the union is a comparatively loose one, and that the 

 immune-body can be dissociated. The phenomenon may 

 in this case be therefore readily explained by the reversi- 

 bility of the combination. This will be discussed in the 

 next section. 



