404 BIOLOGY OF THE LABORATORY MOUSE 



Their presence in cultures of the streptobacillus was not confirmed by van 

 Rooyen (301). 



In ascitic fluid or serum broth the organism typically produces separate 

 cotton-ball or flake-like colonies which are frequently attached to the sides 

 of the tube but settle down to the bottom if disturbed. A clear supernatant 

 fluid is left. Surface growth does not occur. Filtrates of cultures are not 

 infective (301). 



Identification of the organism is made chiefly by the type of growth in 

 liquid media and the morphology. Biochemical reactions are of little 

 help — acid is produced from glucose, salicin, and sometimes lactose and 

 maltose. Serologically, the strains thus far studied are antigenically the 

 same (161, 301). 



Differential diagnosis. — Diagnosis of this disease clinically involves 

 differentiation from three diseases, pasteurellosis, mouse pseudotuberculosis, 

 and ectromelia. Animals infected with Pasteurella may show a rapidly 

 fatal systemic infection, conjunctivitis, paralysis of the hind limbs, and 

 rarely arthritis, but no edema or cyanosis occurs. Mouse pseudotuber- 

 culosis may be differentiated by the absence of conjunctivitis and edema 

 and by the pathological findings. In ectromelia a dry gangrene of the feet 

 and legs is characteristic, paralysis and conjunctivitis are absent, and 

 recovery usually occurs. Final differentiation, however, is made by cul- 

 ture, except in the case of ectromelia where inclusion bodies and the demon- 

 stration of a filterable virus establish the diagnosis. 



Immunity. — Immunity to the disease occurs naturally, as already pointed 

 out. Animals recovered from the spontaneous disease or injected with 

 heat-killed organisms are resistant to further infection. It is interesting to 

 note that neither infection nor the development of immunity has followed 

 the feeding of cultures (198). 



Infection due to pleuropneumonia-like organisms. — Minute pleuro- 

 pneumonia-like organisms have recently been reported as the etiological 

 agents of experimental disease in mice by investigators both in England 

 (70, 72) and in this country (224, 225, 226, 227, 49, 264, 230). The organ- 

 isms are of particular importance to those studying viruses because the 

 agents are filterable and do not grow in ordinary culture media. Thus far, 

 no cases of spontaneous illness in mice have been reported, although the 

 micro-organisms have been found in instances of pulmonary disease in 

 rats (128). The appearance of pleuropneumonia-like organisms has 

 followed inoculation of mice for other purposes with such agents as yellow 

 fever virus, lymphocytic choriomeningitis virus, and the toxoplasma, or by 



