400 A MANUAL OF BACTERIOLOGY 



reverse is the case, and that in a small community where the 

 population had been partly vaccinated and partly not vaccinated, 

 the incidence of plague during the week following vaccination was 

 less among the vaccinated than among the unvaccinated, pointing 

 to the rapid production of protection. 



Anti-plague serum. This is prepared by growing the 

 B. pestis on the surface of agar in plate bottles, washing 

 off and emulsifying the growth, and for the earlier injec- 

 tions the emulsion is heated to 65 C. for one hour, and 

 the commencing dose is ^ part of a flask. The injections 

 are given intravenously at intervals of a week. At the 

 end of three months the bactericidal power of the blood 

 will have become very marked, and living cultures are 

 then injected for a further period of about three months 

 until a whole flask- culture is given at a dose. An interval 

 of a fortnight is allowed to elapse between the last dose 

 and the bleeding of the animal. The serum is tested 

 upon mice. 



The anti-plague serum, which is mainly anti-microbic, 

 is not very potent, and to be of service large amounts and 

 early treatment are essential. 1 



Epidemiology. The mode of infection in man has been 

 a matter of controversy. The pneumonic form arises 

 generally from aerial infection by the respiratory tract. 

 It is extremely fatal and infectious, while the bubonic and 

 septicaemic varieties are hardly ever contagious. Although 

 a gastric and intestinal form of the disease has been 

 described, and there is evidence to show that food or drink 

 may be the vehicle of infection, this must be a rare mode 

 of infection. Yersin claimed to have isolated the bacillus 

 from the dust and earth of a native dwelling, and Hankin 

 from the brackish water in a field. The observations of 

 Hankin and others indicate, however, that contagion is 

 likely to occur only from immediate contact with man or 



1 See Hewlett's Serum Therapy, 1910. 



