490 INFECTION AND IMMUNITY. 



relation to typhoid and cholera, in this instance 

 naturally using plague bacilli (killed) and anti- 

 plague serum. Shiga reported good results by the 

 use of the combined method in the epidemic in 

 Kobe. 



The immunity which is produced by protective 

 inoculation,, like that which follows natural infec- 

 tion, is considered to be antibacterial inasmuch as 

 the serum acquires increased bactericidal power for 

 the bacillus, but shows no ability to neutralize its 

 toxic constituents. The influence of opsonins is 

 essential for experimental phagocytosis, and is an 

 important factor in the mechanism of immunity. 

 Antiplague serum contains also complement-devi- 

 ation antibodies and precipitins. The immunity 

 which follows infection is of long duration. 



serotherapy Prophylactic injections of antiplague serum pro- 

 ana Prophy- -. ., i , 



laxis. duce a temporary immunity of about two weeks 

 duration. The Pasteur Institute prepares the 

 serum of Yersin by immunizing horses first with 

 killed and then with living cultures. The immun- 

 ization is difficult and from several months to a 

 year and a half are required for the production of 

 a strong serum. When the blood is drawn its free- 

 dom from living plague bacilli and from toxic sub- 

 stances must be assured. The immunizing value of 

 the serum is determined by that quantity which 

 will save a mouse from a fatal dose of living plague 

 bacilli, the serum being given 24 hours in advance 

 of the culture. This is accomplished by 0.1 to 0.02 

 c.c., depending on the strength of the serum. Its 

 curative power is estimated from that quantity, 0.5 

 to 0.1 c.c., which saves a mouse when administered 

 16 hours after the injection of an otherwise fatal 

 dose of culture. For protective inoculation in man 



