3 2 4 



METHODS OF IDENTIFICATION AND STUDY 



A slight local reaction will probably be observed as 

 well as the weight and temperature reactions. 



1 1. A week to ten days later inject a similar minimal 

 lethal dose into the peritoneal cavity. 



12. Observe the weight and temperature of the 

 rabbit very carefully, and regulating the dates of 

 inoculation by the animal's general condition, continue 

 to inject living cultivations of the pneumococcus 

 into the peritoneal cavity, gradually increasing the 

 dose by multiples of ten. 



13. At intervals of two months samples of blood may 

 be collected from the posterior auricular vein and the 

 serum tested for specific anti-bodies. 



14. Under favourable conditions it will be found 

 after some six months steady work that the rabbit 

 may be injected intraperitoneally with an entire blood 

 agar cultivation without any ill effects being apparent ; 

 and this characteristic resistance to the lethal effects 

 of large doses of the virus is the sole criterion of 

 immunity. Further, the serum separated from blood 

 withdrawn from the animal about a week after an 

 injection, if used in doses of .01 c.c., will protect a 

 mouse against the lethal effects of at least ten minimal 

 lethal doses of living pneumococci. 



In the foregoing illustration it has been assumed that 

 complete acquired active immunity has been conferred 

 upon the experimental rabbit in consequence of the for- 

 mation of antibody, specific to the diplococcus pneu- 

 moniac, sufficient in amount to ensure the destruction 

 of enormous doses of the living cocci the antigen (that 

 is the substance injected in response to which antibody 

 has been elaborated) in this particular case being the 

 bacterial protoplasm of the pneumococcus with its 

 endo- toxins. 



But provided death does not immediately follow the 

 injection of the antigen, specific antibody is always 

 formed in greater or lesser amount; and in experi- 



