41 



PEST-LIKE BACTERIA FOUND IN RATS. 



The somewhat general impression that there are a considerable 

 number of organisms that are readily mistaken for Bacillus pestis is 

 not justified, provided one gives attention to cultural and inoculation 

 investigations. It is quite true that there are a considerable number 

 of organisms which in smears from tissues are scarcely to be distin- 

 guished morphologically from B. pestis. The similarity, however, 

 usually ends there. A few resemble plague somewhat closely in 

 cultural reactions, and especially B. pseudotuberculosis rodentium 

 (Pfeiffer) should be mentioned here; but these differ in pathogenicity. 

 For example, the above-named organism is not pathogenic for rats. 



Neumans (11) reviews the subject of pest-like organisms patho- 

 genic for rats, and describes an organism belonging to this group 

 which he isolated from the body of a rat. His work clearly shows 

 that none of the organisms that have been described should cause 

 any serious difficulty in the hands of a careful investigator. 



Kister and Schmidt (12) describe an organism closely resembling 

 B. pestis in many respects, and with which guinea pigs could be 

 successfully infected by the cutaneous method. This organism, 

 which was also pathogenic for rats and mice, belongs to the hemor- 

 rhagic septicsemic group. It differed from B. pestis in that it gave 

 no involution forms when grown upon salt agar and was much more 

 rapidly fatal to laboratory animals. 



Augeszky (13) observed an epidemic among gray rats in his lab- 

 oratory which was due to a pest-like organism belonging to the Fried- 

 lander group. The animals died after a couple of days of illness. At 

 the post-mortem examination the spleen was found large, soft, and 

 congested. There was a hyperaemia of the intestines, lungs, and liver. 

 In the spleen were found many, and in the heart's blood few, capsu- 

 lated bacilli, some of which resembled B. pestis. The cultural reac- 

 tions were in nowise similar to those of B. pestis. He found that in- 

 oculation of rats with a pure culture of this organism sometimes killed 

 in as short a time as twenty-four hours, sometimes as late as two or 

 three weeks, and in some cases the lesions were not very unlike those 

 sometimes produced by B. pestis. However, this organism by its dif- 

 ferent cultural reactions, and the fact that the capsule is usually easily 

 demonstrated, would probably never be a source of any confusion. 



ARTIFICIAL INFECTION OF RATS WITH PLAGUE. 



For laboratory purposes in general it is customary to use tame white 

 rats, and in plague work they are especially satisfactory, as they are 

 easily handled, rarely harbor fleas, are very susceptible to the infec- 

 tion, and finally and most important, they frequently die a day or 

 two earlier than guinea pigs. At times it may be necessary to use 



