INFECTIOUS DISEASES OF MICE 407 



organisms which produced the infection just described, both Types B and C 

 have been found in pneumonic lungs (227, 103, 104). A conclusive etiologi- 

 cal relationship has not yet been established for the pleuropneumonia-like 

 organisms found in the lungs of these animals. Sullivan (263) has found 

 that after six consecutive passages of the organism on killed egg membranes, 

 pneumonic lesions were produced by a single inoculation, which makes 

 probable but does not prove a causal relationship. Further work is neces- 

 sary to differentiate this type of pneumonia from that caused by viruses 

 (54, 89, 103, 104). 



The other pleuropneumonia-like organisms isolated from mice (Li, L3, 

 Le and Types B, C, D, and E) produced arthritis in a variable number of 

 inoculated animals. The B strains (226) caused a migratory polvarthritis 

 in almost 100 per cent of mice injected intravenously or intraperitoneally. 

 The disease thus produced is chronic, non-fatal, and often results in ankylosis 

 with a pathological picture of proliferation of joint structures. The Le 

 strain causes arthritis in about 30 per cent of mice, whereas the Li strain 

 only occasionally affects the joint (72). Dienes and Sullivan (50), however, 

 have not succeeded in producing infection in mice with the Li organism. 

 Production of toxin by these strains has not been demonstrated. 



The experimental disease (72) produced in mice by inoculation of the L7 

 strain, obtained from rats showing polyarthritis, is of considerable interest 

 because of its similarity to that described above as caused by Streptohacillus 

 moniliformis. In some animals swelling of the tibiotarsal joint, edema of the 

 subcutaneous tissues, and death followed inoculation of the foot pad with 

 cultures mixed with agar. With intracerebral inoculation, weakness of 

 the hind legs, hunched back, tremors, turning in circles, and occasionally 

 conjunctivitis developed. Intravenous and intraperitoneal administration 

 resulted in pleural or peritoneal exudation and arthritis in animals surviving 

 48 hours or longer. Intranasal instillation produced pneumonia in 5 to 8 

 days. In smears of animal tissues rings, granules, and comma-shaped 

 structures were seen. In spite of the fact that the Li strain, apparently 

 associated with StreptobaciUus moniliformis, and the L7 strain are distinct 

 and separate organisms, the points of similarity between the two diseases 

 provide an adequate basis for etiological confusion. 



In general, animals other than the mouse are resistant to infection with 

 mouse strains, and even among mice considerable variation in susceptibility 

 is found between individuals and breeds. Mice surviving experimental 

 inoculation are resistant to reinjection with the same strain although no 

 humoral antibodies are demonstrable. 



