INFECTIOUS DISEASES OF MICE 417 



At autopsy the only gross lesions were found in the liver, which was 

 enlarged and contained a varying number of opalescent, grey or yellowish 

 nodules. These nodules were usually discrete, varying from less than 0.5 

 mm. to more than 2.0 mm. in diameter (Fig. 161). Microscopically, the 

 lesions were situated in close proximity to the portal vein, suggesting an 

 embolic distribution. They consisted of necrotic tissue with an extensive 

 peripheral polymorphonuclear infiltration. Hepatic cells about the lesions 

 contained many long, slender bacilli, lying roughly parallel to one another, 

 each organism separated from the adjoining one (Fig. 162). Numerous 

 spores were present as well as vegetative forms apparently undergoing 

 sporulation. Organisms were frequently 

 present in the gall bladder and bile. 

 Although no visible lesions were present 

 in the alimentary tract, microscopic sec- 

 tions of the cecum and first portion of 

 the large intestine revealed many bacilli 

 and spores within epithelial cells, 

 phagocytes, lymphatics, and in the 

 depths of the glands (Fig. 163). Almost 

 no host reaction was present. 



The organism was a slender, non- Fig. 161.— 5. pUijormis infec- 



motile, non-acid fast, gram-negative tion in mice; gross appearance of 

 bacillus, showing considerable pleomor- lesions in liver. {From Tyzzer, J. 

 phism. Some organisms presented a ^ ^ ' 



granular, band-like appearance. Spores were situated sub terminally. 

 One attempt to demonstrate the heat resistance of the spores was incon- 

 clusive, but a contaminated cage remained infective after one year at room 

 temperature. All attempts to grow the organism in pure culture on enriched 

 culture media failed, except for one occasion when it grew briefly in symbiosis 

 with a streptococcus. 



Infection could be best produced experimentally by contact of susceptible 

 mice with diseased ones or with a contaminated cage, and by ingestion of 

 infected tissue or intestinal contents. Common laboratory mice, rabbits, 

 and guinea pigs were resistant. Intravenous injection of waltzing mice 

 with large doses produced the t>'pical liver lesions and death, but minimal 

 lesions and immunity followed small doses. Intraperitoneal and subcuta- 

 neous administration did not result in systemic disease. On the basis 

 of these findings, together with the pathological picture, Tyzzer 

 postulated that the fatal disease was produced by a secondary embolic 



