200 STUDIES IN IMMUNITY. 



corpuscles remain intact even after a long time. But if a small 

 amount of fresh rabbit serum is added to the mixture, a rapid dis- 

 solution takes place, although this added serum is in itself harmless 

 for the corpuscles. This shows that the original mixture contained 

 an excess of sensitizing substance, as demonstrated by the destruc- 

 tion of the corpuscles on the addition of normal rabbit serum. 

 Consequently, although the original mixture did not affect the cor- 

 puscles, there was no lack of sensitizing substance and the protec- 

 tion is due to the neutralization of the guinea-pig alexin also 

 present in the fresh hemolytic serum by the antitoxin. 



To show the anti-alexic activity in another way we prepare a mix- 

 ture of 1 c.c. of fresh normal guinea-pig serum and 2 or 3 c.c. of 

 antitoxin (55 degrees). As a control a mixture 1 c.c. of fresh guinea- 

 pig serum and 2 or 3 c.c. of normal rabbit serum (55 degrees) is 

 also made. To each mixture is added a strong enough dose of sen- 

 sitizing substance (heated hemolytic serum) to resist neutralization 

 by the antitoxin; rabbit corpuscles subsequently added to each 

 mixture remain intact in the first and are destroyed in the second. 

 To make this experiment more conclusive a second control may be 

 prepared containing, like the first, antitoxin and sensitizing sub- 

 stance, but with the normal guinea-pig serum replaced by an equal 

 amount of normal rabbit serum. This mixture destroys corpuscles, 

 which proves that the dose of sensitizing substance used was larger 

 than could be destroyed by the antitoxin; and it proves also that 

 our antitoxin although effective against guinea-pig alexin has no 

 effect on rabbit alexin. 



The idea that antitoxin has only a weak " antisensitizing " power 

 whereas it has a very much more distinct " anti-alexic " power 

 explains very clearly the fact that we have already noted, namely, 

 that heated antitoxin combats the effect of fresh hemolytic sera 

 better than non-heated antitoxin. A moderate dose of antitoxin 

 added to fresh hemolytic serum may neutralize the alexin of this 

 hemolytic serum, but leave a certain amount of sensitizing substance 

 still active. 



If the antitoxin has not been heated, it contains an additional 

 dose of alexin, which aids in the destruction of corpuscles thr scn- 

 sitization of which it has not been able to prevent. When heated 

 to 55 degrees it does not have this disadvantage; it has then only 



