A GENERAL RESUME QF IMMUNITY. 517 



this dyeing is a physical or chemical phenomenon, but simply to 

 determine whether there are analogies in the mode of reaction 

 between the paper and the dye on the one hand, and antibody and 

 antigen on the other. 



Our knowledge of adsorption owes much to the study of col- 

 loids. Certain authors, indeed, who agree with me in recognizing 

 the great importance of molecular adhesion in serum reactions, 

 have become accustomed to say that the union of the antibody 

 with the antigen represents a reaction between two colloids. It 

 seems to me a little rash to define so clearly and I should prefer to 

 speak of this union as an adsorption phenomenon. Adsorption, 

 indeed, is evident, not only between two colloids but also between a 

 colloid or suspended particles on the one hand and a substance in 

 true solution on the other, and although it is very probable that 

 antibodies are really colloids we cannot with certainty say as much 

 of the antigens. It may be remarked in respect to colloids that too 

 much importance has frequently been attached to the appearance 

 of agglutination as an indication of the formation of a complex. 

 The agglutination is a secondary phenomenon as Neisser and Fried e- 

 mann, Bechhold, Biltz, Henri and Girard Mangin, and others have 

 correctly stated, and its manifestation depends in large measure on 

 certain conditions such as the relative proportions of the two sub- 

 stances concerned, temperature, presence of electrolytes, etc. The 

 principal and essential fact is the affinity of adhesion produced by 

 the union, but such a union may give rise quite as well to dissemina- 

 tion, that is, a more stable and perfect condition of emulsion, as to 

 the formation of flecks ; in his researches on adsorption by chemical 

 precipitates, Gengou has insisted on this fact and shown that slight 

 physical modifications of the substances concerned without any 

 chemical change may give rise to dissemination instead of clumping, 

 or the reverse. Forges has noted similar facts. 



Can certain characters, such as reversibility or the rapidity of 

 reaction, be called upon to prove whether the union of two sub- 

 stances belongs or not in the category of adsorption phenomena? 

 In this respect we should note, particularly, that the affinity of 

 adsorption varies greatly in different cases and these differences of 

 intensity are evident by the more or less rapid union and the more 

 or less stable resulting complex. As Van Bemmelen has mentioned, 



