INFECTIOUS DISEASES OF MICE 



437 



toxylin may be used. After chromic acid fixation, methylene blue gives a 

 characteristic picture. 



The experimental disease. — The disease can be transmitted to normal 

 mice bv inoculation of edema fluid, blood, or various tissue emulsions from 

 infected animals. Blood plasma is infective from i to 5 days after the 

 appearance of the lesions, the liver and spleen after 3 days. Intradermal 

 inoculation in the foot pad usually reproduces the cutaneous type of disease. 

 Intraperitoneal or intravenous injection produces the acute form, with 



Fig. 169. — Infectious ectromelia: section of skin showing edema, necrosis, and 

 inclusion bodies in the epithelial cells. Hematoxylin-eosin. (X360.) {From 

 Birsch-Hirschfeld.) 



death in 4 to 6 days. A disseminated pneumonia follows inhalation of the 

 virus. Transmission of infection also occurs by permitting contact of 

 normal and infected mice under ordinary conditions, which has permitted 

 study of experimental epidemics of the disease (92, 119). 



Properties of the virus. — The virus responsible for this disease may be 

 isolated from the liver, spleen, central ner\-ous system, lymph nodes, lungs, 

 peritoneal and edema fluids, and blood. It is filterable through diatoma- 

 ceous or porcelain filters (Chamberland L2, Mandler, Berkefeld X)and has an 

 estimated size of 100 to 150 m/i ( i8). It is resistant to dr}'ing in a desiccator, 

 may be preser\-ed for months in 50 per cent glycerin at o°C., but is inacti- 



