PATHOGENIC BACTERIA. 265 



taneously with micrococci. The bacilli are numerous in the 

 enlarged lymph-nodes, but may be detected in the other organs 

 of the body and in the blood. The organism is formed in the 

 fluid drawn with a hypodermic needle from bubo during life. It 

 may be cultivated from this fluid, and recovered from rats and 

 guinea-pigs inoculated with it. In the pneumonic or pulmon- 

 ary form the bacilli occur in the sputum, and may be tested 

 in the same manner. This type of the disease is said to be 

 very fatal. In the septicemic form no primary bubo is found; 

 but a bubonic case may become septicemic, and this form is 

 very fatal. 



During epidemics of plague it has been noted that rats may 

 die in large numbers, and plague bacilU have often been re- 

 covered from the bodies of such rats. The systematic de- 

 struction by health departments of all the rats possible is im- 

 portant where an epidemic is present or is feared. The same 

 apphes to mice. The agency of fleas as carriers of the bacilli 

 has been suggested, but has not yet been proved; this is equally 

 true as to flies. 



The greatest care must be used in working with the bacillus 

 of plague. A number of fatal results have occurred through 

 it in laboratory investigators. 



Haffkine has devised a method of protective inoculation 

 against plague consisting of the injection of cultures of plague 

 bacilli which have been sterilized by heat, with a little carboUc 

 acid added. An active immunity which is quite lasting, it is 

 maintained, may be secured by this method in some days. 

 The injection is sometimes followed by considerable consti- 

 tutional disturbance. This method seems Hkely to be of con- 

 siderable value. 



Yersin and others have prepared protective sera on the 

 same general principles used in making other sera for effect- 

 ing passive immunity. The results so far obtained with these 

 sera are vtry encouraging. 

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