A GENERAL RESUME OF IMMUNITY. 521 



with it. They have also found that dilution renders neutralization 

 much more difficult and that different mixtures are obtained depend- 

 ing on whether they mix the toxin and the antitoxin, after diluting 

 them, or dilute the toxin-antitoxin mixture. This fact is evi- 

 dently not in favor of the Arrhenius-Madsen theory, according to 

 which the same state of equilibrium should exist in both instances 

 owing to reversibility, and the same fraction of the toxin of necessity 

 remain free. 



The fact which lends significance to the researches of Grassberger 

 and Schattenfroh, and which prevents their applying Ehrlich's 

 interpretation, is that the toxic fluid which they employ contains 

 in reality a single poison; there is no reason for assuming the exis- 

 tence of toxoids, inasmuch as the toxic power of the poison shows 

 itself constantly parallel to its neutralizing power for antitoxin. 



Among the facts which have most contributed to strengthen the 

 idea of a union in variable proportions (an idea which is so highly 

 compatible with the adsorption theory) and which, moreover, have 

 shown that the complexes obtained frequently manifest only a very 

 incomplete reversibility, there should be mentioned in particular 

 those which have been observed by employing the method which I 

 used for hemolysins in 1900 and which may be called "the method 

 of addition of the antigen to the antibody in single or in divided 

 doses/' A given volume of hemolytic serum may destroy more 

 or less corpuscles in accordance with their introduction in one or 

 several doses separated by sufficient intervals. As we know, other 

 authors have since performed similar experiments with the same 

 results, employing antitoxin and toxin in place of hemolysin and 

 corpuscles (Danysz, von Dungern, and Sachs) or using bacteria and 

 agglutinins (Craw). It seems to me proper in this connection to 

 mention the comparison with dyeing phenomena, and on this 

 point I agree entirely with Craw. If a large piece of filter paper 

 is placed in a certain volume of sufficiently diluted dye it takes a 

 uniform shade of intensity; if, on the other hand, the same sized 

 piece of paper is cut up in pieces and added in fragments, the first 

 pieces are stained deeply and the last find no color left. In the 

 same way, on adding toxin to antitoxin in divided doses the last 

 portions of the poison cannot be neutralized as the first are super- 

 saturated with antitoxin. When the entire mixture is made at 



