INFECTIOUS DISEASES OF MICE 381 



ically pure strains, steps may be taken to prevent spread of the infection 

 and destruction of the colony. The mouse must also be regarded as a 

 reservoir of certain animal and human diseases. These considerations have 

 led to the inclusion in this volume of a summary of the literature concerned 

 with the natural diseases to which mice are subject. Other general descrip- 

 tions of diseases in mice may be found in the works of Jaffe (no), Meyer 

 (172), and others (299, 87, 170). 



Bacterial Diseases 

 Mouse Typhoid 



In 1890, a highly fatal epidemic occurred in the laboratory mice of the 

 Hygienic Institute at Greifswald, 69 per cent of the animals succumbing 

 (154) to the infection. Loeflier noted the large, brownish-red spleens and 

 the small yellow lesions in the livers of dead animals. Groups of organisms 

 in capillaries reminded him of typhoid bacilli in human tissues. His studies 

 of this bacillus showed that it was closely related to the colon-typhoid group 

 and accordingly the name '^B. typhi murium'' was proposed. Subsequent 

 investigations have revealed that this strain and related organisms of the 

 paratyphoid {Salmonella) group produce one of the most important bacterial 

 diseases of mice. 



Occurrence. — Mouse typhoid occurs so commonly in rodents that only 

 with elaborate precautions can a colony be maintained free from infection. 

 Animals suffering from the chronic form of disease may harbor and excrete 

 the organism for months, thus maintaining infection in the colony; or the 

 infection may be introduced from without in the food or from wild rodents 

 gaining access to the animal rooms. Salmonella typhimurium and S. 

 enteritidis are found with about equal frequency in apparently healthy wild 

 and laboratory mice and as the cause of epidemics (47, 235, 335, 236, 113, 10, 

 159, 336, 26). The incidence of carrier infection in stock mice may vary 

 from I to 20 per cent and rarely to 100 per cent (307, 172, 330). Other 

 paratyphoid strains are uncommon, although epidemics due to IMorgan's 

 bacillus (Proteus morgani) (337) and an unknown species of Salmonella (265) 

 have been reported. 



The natural disease. — Salmonella infections in general are bacteremic 

 diseases and may run acute, subacute, or chronic courses. The various 

 bacilli produce essentially the same clinical picture. Infection as a rule 

 takes place by the oral route and the incubation period extends from 3 to 

 6 or more days. The first sign of illness is a loss of normal activity and 



