184 STUDIES IN IMMUNITY. 



similar diminution, as already stated, may be noted on heating 

 rabbit antihen serum to a temperature of 70 degrees. 



The sensitizing property of cholera serum from the guinea-pig 

 is weakened by heating to a lower temperature than 70 degrees, as 

 is true of its immobilizing and agglutinating property ; the weaken- 

 ing, indeed, is very distinct even on heating to 65 degrees. 



Are there sensitizing properties in normal sera? Is not the action 

 of the alexin in these sera aided by some other substances? It is 

 difficult to answer these questions because, so far, we have not suc- 

 ceeded in separating alexins from the other substances present in 

 serum. On combining two normal sera, however, the existence of 

 a sensitizing property may sometimes be shown. For example, 

 cholera vibrios, immobilized and agglutinated by horse serum, are 

 easily transformed to granules on the addition of normal guinea- 

 pig serum. No generalized statement, however, should be made on 

 the basis of this observation; it is not safe to conclude that it suffices 

 to agglutinate bacteria or corpuscles in order to sensitize them to 

 the action of alexin. For example, rabbit red blood corpuscles, 

 although strongly agglutinated by heated hen serum, are no more 

 susceptible to the slight dissolving effect of normal guinea-pig serum 

 than are normal rabbit corpuscles. The presence of agglutination, 

 then, does not indicate any particular sensitivity to alexin. An 

 answer to these questions will necessitate further study. 



CONCLUSIONS. 



I. The serum of animals treated with defibrinated blood from a 

 different animal species shows active properties, consisting in the 

 agglutination and energetic dissolution of corpuscles similar to 

 those used for injection. There is also in certain instances a power 

 to produce a precipitate with serum (or defibrinated blood) similar 

 to that used in immunization. 



II. The dissolving action of the active serum on corpuscles is 

 due to the presence of two substances: one that belongs properly 

 to the active serum; the other (alexin) which occurs not only in 

 active sera but also in normal sera. The first substance acts by 

 sensitizing the corpuscles to the action of the second substance. 

 These facts are strictly comparable with those already established 

 by us for cholera serum and the cholera vibrio. 



