116 IMMUNITY. 



it to 55 C.; the ordinary blood-serum culture-medium illus- 

 trates this destructive action. 



Germicidal power of the blood causes : This bacteriolytic 

 action is especially marked in the cases of those bacteria to 

 which the animal is naturally immune. There are exceptions 

 to this rule, however. The rabbit is very susceptible to anthrax 

 even though its blood is markedly germicidal for the anthrax 

 bacillus. It is possible that this action of the blood is not sc 

 much germicidal as attenuating, thus antagonizing the toxi- 

 genic power of the bacterium and enabling the tissues to 

 dispose of the germ. 



Behring attributed this germicidal action to the alkalinity 

 of the blood. Buchner, after very exhaustive studies of this 

 subject, concluded that the germicidal properties of the blood 

 are due entirely to its soluble constituents, which he termed 

 alexins. Hankin ascribed it to the germicidal globulins, 

 which he named defensive proteids. They are destroyed by 

 heating to 55-60 C. for one-half hour, and by diluting 

 with from eight to ten volumes of distilled water. Vaughan 

 and McClintock attribute the germicidal action to the nucleins, 

 and believe that immunity diminishes as these substances 

 become less soluble. They extracted nuclein from the blood- 

 serum and demonstrated its germicidal property. 



Buchner's alexins are not nucleins. The alexins are de- 

 rived from the leucocytes, especially the amphophiles. which 

 Hankin calls the alexoeytes, Buchner found that when the 

 leucocytes disintegrated, a germicidal substance is liberated, 

 showing that the germicidal action of the blood is not clue 

 to phagocytosis. It is probable, therefore, that the living 

 leucocyte secretes a substance on which the so-called pha- 

 gocytic action depends. Although the exact nature and 

 composition of these alexins are not definitely known, they 

 in all probability have their origin in the white cell of 

 the blood, in which also resides the germicidal power of 

 the blood. 



Plasmolysis may also be of some importance in this con- 

 nection. The removal of a germ from an isotonic to a hyper- 

 tonic or hypotonic medium in all probability has an injurious 

 effect on the organism. While this does not account for the 



