176 ESSENTIALS OF BACTERIOLOGY 



Staining. Are stained with the ordinary dyes, but Gram's 

 method negative. 



Pathogenesis. When experiment animals, mice or guinea- 

 pigs, are injected with a pure culture under the skin, they die in 

 eight to fifteen hours, and the following picture presents itself 

 at the autopsy: In guinea-pigs from the point of infection, 

 spreading over a large area, an edema of the subcutaneous 

 tissues and muscles, which are saturated with a clear red serous 

 exudate, free from smell, containing great quantities of bacilli. 



Fig. 109. Smear of pus of chancroid of penis (x !5o) (Davis) (photo- 

 micrograph by Mr. L. S. Brown). 



The spleen is enlarged, especially in mice. The bacilli are 

 not found in the viscera, but are present in great numbers on 

 the surface, i. e., in the serous coverings of the different organs; 

 though when any length of time has elapsed between the death 

 of the animal and the examination, they can be found in the 

 inner portions of the organs, for they grow well upon the dead 

 body. In man they have been found in rapidly spreading gan- 

 grene. They are present in the soil, in putrefactions of various 

 kinds, and in dirty water. 



Immunity. Is produced by injection of the sterilized cul- 

 tures, and also the filtered bloody serum of animals dead with 

 the disease. 



