IMMUNIZATION. 547 



against the staphylococcus by immunization with 

 pure cultures. 4 



One may immunize either with living or killed 

 cultures or with culture filtrates. Immunization 

 with the bacterial cells must proceed slowly in 

 order to avoid killing the animals. When filtrates 

 containing leucocidin or staphylolysin (hemolysin) 

 are used, antitoxins for these substances are 

 formed. The antistaphylolysin obtained for one 

 strain neutralizes the hemolysin of all strains. 

 The most prolonged immunization with bacterial 

 cells causes no appreciable increase in bacterioly- 

 sins. 



The serum of one who has recovered from a Protectio 

 staplrylococcus infection, or that of immunized an- 

 imals, is protective for other animals; 0.1 to 0.2 

 c.c. of an immune serum given subcutaneously 

 protected mice from a fatal dose of cocci given 

 two hours later, whereas other mice were killed in 

 from 8 to 12 hours. When the serum was given 

 24 hours in advance of the culture, from 0.02 to 

 0.03 c.c. saved them (v. Lingelsheim, cited by 

 Neisser). The results of Petersen and of Proscher 

 were similar. In spite of this rather strong pro- 

 tective action, immune serums have little or no 

 curative power. 



No clearer explanation of the action of the im- Properties 

 mune serum is given than that afforded by the 

 experiments of Proscher, who injected guinea- 

 pigs, rabbits and mice with normal and immune 

 serums and followed this 24 hours later with in- 

 oculation of the cocci into the peritoneal cavity. 



4. Their experiments in protecting and curing other ani- 

 mals with antistaphylococcus serum represent the first at- 

 tempt made in the direction of passive immunization. 



