INFECTIOUS DISEASES OF MICE 403 



The experimental disease. — Types of infection entirely similar to the 

 spontaneous disease may be produced by inoculation of pure cultures. 

 Intravenous or intraperitoneal injection produces the acute septicemic form 

 of the disease; subcutaneous or intra-articular administration, or instilla- 

 tion into the conjunctival sac results in the chronic disease described above. 

 Mice show considerable variation in their susceptibility, not only individ- 

 ually but genetically. Albino strains are more susceptible than the wild 

 brown mouse or hybrid black-coated stock. Other animals in general are 

 relatively resistant to infection. 



Etiology. — The organism is a facultative aerobe which grows on liquid 

 or solid media containing 40 per cent or more of serum. Loeffler's medium 



Fig. 158. — Film from a culture of StrzptobacUhis moniliformis immediately after 

 isolation. Basic fuchsin. (X900.) {From van Rooyen.) 



or scrum agar is very satisfactory for its isolation. Morphologically, marked 

 pleomorphism occurs in recently isolated cultures; slender gram-negative 

 bacilli, coccoid bodies, and interlacing filaments are present. Large fusi- 

 form, oval, or club-shaped swellings may occur at any point in the filaments. 

 After repeated transplants, the morphology becomes more regular and 

 bacillary in form (Fig. 158). 



On the surface of solid media, the colonies are of fair size (i to 2 mm.), 

 greyish, translucent, but not particularly characteristic. Around the colony, 

 often imbedded in the agar, tiny microscopic colonies with dark centers may 

 be found (125, 126, 48). These are the Li colonies (referred to above), 

 morphologically characterized by large bodies, granules, and filaments. 



