100 STUDIES IN IMMUNITY. 



destructive effect of alexin. This alexin or lysin is the bactericidal 

 or globulicidal substance that is destroyed at 55 degrees, and affects 

 certain delicate cells as a sort of digesting diastase. The specific 

 properties of these sera resist heating to 55 degrees or 60 degrees. 



3. The sera when fresh contain alexin; and it is due to the 

 presence of this substance that they are able to alter profoundly 

 or to cause partial dissolution of those cells which they sensitize. 



If we were to enumerate the really essential properties of these 

 sera we might eliminate the third, namely the possession of alexin, 

 as this substance is also present in the serum of normal animals. 

 After destroying this alexin in the specific serum by heating it to 

 55 degrees and so removing its bactericidal or globulicidal power, 

 the power may be Testored by the addition of a small amount of 

 normal serum which contains alexin.* 



There remain then two other properties, which, to be sure, occur 

 in normal sera to a slight extent, but may be considered as charac- 

 teristic of the serum of vaccinated animals. 



We shall not consider here the question as to whether these two 

 properties are due to two distinct substances or are to be attributed 

 to the action of one and the same substance, reserving such dis- 

 cussion for another time. In all events the most remarkable of 

 these two properties is the sensitizing of cells to the action of the 

 alexin. When we say that there exists in specific sera a sensitizing 

 substance (substance sensibilisatrice) it implies that these sera act 

 directly on the cells. Indeed this sensitizing substance has a par- 

 ticular predilection for fixing itself on those cells which it affects. 



When cholera vibrios are placed in a suitable amount of fluid 

 containing cholera serum they absorb its active principles. After 

 centrifugalizing and decanting the clear supernatant fluid is found 

 to have lost both its agglutinating power and its power of sen- 

 sitizing new bacteria to the action of the alexin. In other words, 

 new vibrios, when placed in contact with this fluid, are not immo- 

 bilized or agglutinated and may be injected into the peritoneal cavity 

 of a guinea-pig or mixed with normal guinea-pig serum in vitro with- 

 out showing granular transformation. The same phenomenon of 

 absorption or fixation occurs if the vibrios are cultivated in bouillon 



* The details of these experiments for the cholera vibrio will be found in the 

 article beginning page 50, and for the red blood cells in the article on page 134. 



