206 CLINICAL BACTERIOLOGY. 



patients and observation of those by whom they are sur- 

 rounded are naturally necessary. 



Immunity and Protective Inoculation. Plague-bac- 

 teria retain their virulence until shortly before death. It is, 

 therefore, impossible to immunize susceptible animals with 

 old cultures (German Commission). Slightly susceptible 

 animals can be readily immunized by increasing doses of 

 living bacilli. Highly susceptible animals must, however, 

 be treated carefully with dead cultures. For this purpose 

 it is best to employ cultures that have been exposed for an 

 hour to a temperature of 65 C. (149 R). In subjecting 

 a brown ape to protective inoculation the Commission em- 

 ployed a heated agar streak-culture. Seven days later the 

 animal was immune to subcutaneous' infection, but only after 

 it had recovered from this was it protected against intra- 

 peritoneal inoculation. Filtered bouillon-cultures possess 

 only slight immunizing properties. 



HafTkine has employed his method of protective inocu- 

 lation, which he first recommended for cholera, also in the 

 treatment of plague. A fluid preparatidh, made from care- 

 fully devitalized plague-bacilli, is injected in doses of from y 2 

 to 2 Y?, cu. cm., in accordance with the age of the individuals. 

 Slight reaction follows, and the injection is repeated in a 

 somewhat larger dose after the lapse of eight or ten days. 

 The results obtained with Haffkine's method are not un- 

 favorable, but a definite decision as to its value must be de- 

 ferred for the present ; at any rate, the protection conferred 

 is not absolute. 



A plague-serum is prepared in the Pasteur Institute for 

 therapeutic purposes from the blood of highly immunized 

 horses. In the observations of the German Commission, 

 three cubic centimeters of this serum sufficed to protect 

 brown apes against subsequent subcutaneous infection. As 

 much as ten cubic centimeters, however, did not suffice to 

 protect susceptible gray apes. The serum exhibits, also, 

 an undoubtedly curative action (after twelve hours) in pre- 

 viously inoculated brown apes. With regard to its efficacy 

 in cases of plague, nothing definite can as yet be stated. 



