394 BIOLOGY OF THE LABORATORY MOUSE 



by the enteral route and the pathological lesions consist of whitish-grey 

 nodules in the intestinal lymph follicles, swelling and caseation of mesenteric 

 nodes, and enlargement of the liver and spleen which contain numerous 

 nodules varying in size. After subcutaneous inoculation, caseation develops 

 locally and in the regional glands. Grossly the lesions may resemble those 

 of tuberculosis or Salmonella infections. Microscopically, however, the 

 lesions are exudative in character and consist of central necrotic material 

 and bacilli surrounded by a zone of leukocytes and histiocytes. In the 

 liver foci of degenerated hepatic cells may be found. The organism is dis- 

 tinguished from P. pestis with difficulty, both culturally and serologically. 



Plague in mice. — Infection with Pasteur ella pestis is very rare in mice. 

 Sporadic cases and epidemics, however, have been reported among field 

 mice in Mongolia and in the Kirghiz Steppes (339), where the disease is 

 maintained by rodent host-reservoirs. Typical hemorrhages and buboes 

 were found at autopsy, and the pest bacillus was isolated from nodules in 

 the viscera. 



Pseudotuberculosis of mice. — Pseudotuberculosis is a term applied to 

 a number of diseases in which the gross lesions resemble those produced by 

 the tubercle bacillus. Its etiology is varied and includes such agents as 

 Salmonella organisms, P. pseudotuberculosis (see preceding section), para- 

 sitic infections, and others. The form described here is limited to mice and 

 is produced by an organism of the genus Corynehacterium. It was first 

 reported in 1894 by Kutscher (135), who isolated the bacillus from the lung 

 of a mouse dying spontaneously. 



The natural disease. — Sporadic infection is usual in this disease, but 

 mild epidemic spread may take place in laboratory stocks of mice (25, 8, 

 216, 286, 94). Its occurrence is relatively infrequent; its course chronic in 

 character. Existence of the infection is frequently suspected by the dis- 

 covery of a caseous lesion of the lung or a lymph node of an otherwise 

 apparently normal animal. Infection presumably occurs by the respiratory 

 or enteric route, carriers and the rodent habit of cannibalism serving to 

 maintain the disease. Distribution of the organism in the animal's body is 

 by way of the blood stream. 



Kutscher's original description gives an excellent picture of the usual 

 postmortem findings. The upper lobe of the right lung was transformed 

 into a greyish- white, friable, caseous mass, with marked inflammatory 

 change in the remainder of the lung. Multiple small nodules, resembling 

 tubercles in appearance and consisting of inflammatory foci, were present 

 in the left lung. The only other significant findings were a massive right 



