148 THEORIES CONCERNING IMMUNITY 



It is not the serum, the blood or other injected heterol- 

 ogous albumin which becomes the "poison" at the time of 

 the second injection since it is always the same substance 

 which is injected, without having undergone any kind of 

 change. If the animal becomes ill after the second injection 

 the necessary conclusion is that he, his blood, his fluid or his 

 tissues were modified by the first injection. 



In what does this modification consist? 



As already seen in the experiments of Pfeiffer, of Krauss, 

 and of J. Bordet, there is formed in the blood of the injected 

 animal, a substance which precipitates when mixed in certain 

 proportions with the injected albumin. This substance was 

 called by Krauss "precipitin" or "precipitating antibody." 



MECHANISM OF ANTI- ANAPHYLAXIS. 



We have seen in the experiments of Hamburger and Moro 

 that the antibody appears only after a longer or shorter 

 period of incubation, and that this appearance coincides with 

 the disappearance of the antigen from the organism of the 

 treated animal, and with the moment when the treated 

 animal becomes hypersensitive. 



We saw also, in Besredka's experiments, that the "period 

 of incubation" increases in length with the dose of injected 

 antigen, which means, as was seen in the previous experiment, 

 that the length of time taken by the antigen to disappear 

 increases with the quantity of the injection. 



Therefore assuming that for a certain quantity of antigen 

 the incubation period is twelve days, if an equal dose of 

 antigen is injected six days after the first injection, the incu- 

 bation period will be prolonged, and the animal will endure 

 a third injection on the twelfth day without showing any 

 sign of trouble. 



Therein lies the explanation of the phenomenon of Rosenau 

 and Anderson and of Otto. 



A similar explanat on applies to the anti-anaphylaxis of 

 Besredka. In order to cause an anaphylactic shock, it is 

 necessary to inject into the prepared animal, who already 

 is in a state of anaphylaxis, a particular dose of antigen. 



