A GENERAL RESUME OF IMMUNITY. 515 



tion phenomenon which does not depend on a strictly defined atom 

 group. It is probable that the properties of molecular adhesion in 

 a corpuscle-sensitizer complex may be modified by the addition of 

 a third element, the antisensitizer, and that the tendency for alexin 

 adsorption will disappear correlatively. In the same way the tend- 

 ency of barium sulphate to fix itself on corpuscles disappears when 

 the particles of this substance have been previously adsorbed by 

 gum, by certain albuminoids, or by sodium citrate. 



And finally the recent researches of Dr. Oswald Streng have 

 shown that the anti-alexins act in the same way as the antisensi- 

 tizers. Horse alexin becomes fixed easily on guinea-pigs' corpuscles, 

 but inasmuch as it is only slightly hemolytic it does not destroy 

 them. These corpuscles, which have fixed alexin, are henceforth 

 capable of giving a reaction with the conglutinin of bovine serum; 

 when mixed with this serum (previously heated to 56 degrees) they 

 are energetically agglutinated. If we take, as Sachs did, guinea-pig 

 corpuscles laden with horse alexin, and treat them with anti-alexin, 

 that is to say, heated serum from a rabbit immunized against horse 

 serum, and then test them with bovine serum, we obtain no con- 

 glutinin reaction. The anti-alexin, then, has neutralized the alexin 

 which has been fixed to the corpuscles and has cured them by causing 

 the property which the alexin produced, namely, that of adsorbing 

 conglutinin, to disappear. And yet the alexin that has been fixed 

 with corpuscles has no free group, and so far as it is concerned no 

 explanation similar to the one proposed for sensitizer and anti- 

 sensitizer by Ehrlich and Sachs can be accepted. 



*** 



Inasmuch as we have no explanation of specificity we must put 

 aside for the moment the question as to why such and such an anti- 

 body unites with such and such an antigen. But even if the under- 

 lying reason for this combination escapes us, we can at least endeavor 

 to determine how this combination is brought about, that is to say, 

 can trace its development. Attempts, therefore, have been made 

 to define the characters of the reaction and to determine in what 

 category of phenomena it belongs. The reader doubtless knows the 

 opinions which have been offered on this subject. Certain authors 

 thought that this reaction should be likened to chemical phenomena, 

 properly speaking, as they exist either between substances endowed 



