NATURAL IMMUNE BODIES 51 



Alexins. It has been found by numerous observers, that nor- 

 mal blood serum is germicidal for many bacteria, and pecu- 

 liarly active substance that is contained in the serum, was called 

 by Buchner Alexin. This dissolves bacteria and destroys them. 

 It also destroys the red blood cells of other animals. The alexin 

 of a dog's serum dissolves the red cells of a rabbit; it is therefore 

 hamolytic. It also is thermolabile, that is, its properties are 

 destroyed by heat (55C.). It is identical with the complement 

 of Ehrlich, and the cytase of Metchnikoff. 



The complement, as it will hereafter be called, takes, as already 

 stated, an active part in bacteriolysis, or bacteria-dissolving, and 

 in haemolysis, or blood-dissolving, it is present hi normal non- 

 immune sera. R. Pfeiffer found that if some serum from a guinea 

 pig immunized against cholera spirilla is injected into the peri- 

 toneal cavity of a healthy non-immune guinea pig, with some 

 cholera spirilla, that the latter are agglutinated, and ultimately 

 dissolved, having undergone bacteriolysis (Pfeiffer's reaction). 

 The immune serum alone in a test-tube, with the cholera spirilla 

 does not have this action, but if some normal guinea-pig serum 

 is added to the mixture, an immediate solution takes place, 

 showing that the presence of both the normal serum containing 

 the complement, and the immune serum, containing the immune 

 body, or amboceptor, are necessary to complete the solution of 

 the bacteria. If the complement is heated above 55C. for an 

 hour, solution does not take place, even if the immune serum is 

 present, but, after heating the mixture, it may be reactivated by 

 adding some fresh unheated complement. The complement is 

 thermolabile, i.e., destroyed by heat. 



The immune serum is not affected by heat, and is therefore 

 called thermostabile. 



These various reactions may be expressed concretely thus: 



Bacteria + immune body = no solution. 

 Bacteria + complement = no solution. 



