ON EPIDEMICS AMONGST MICE. {303 



The opportunity for the pulverisation of bacilli in the straw is 

 very favourable. The diffusion of germs through the air, if it 

 happens at all (and I have not studied this mode of infection 

 experimentally), is certainly of very subordinate importance. In 

 the second mouse-cage, which stood close to that which contained 

 the diseased mice, there was no infection. 



The duration of the epidemic was somewhat lengthy. Eight 

 mice were isolated on the 25th of October, and the last of these 

 did not die until the 7th of November. If we assume that this 

 mouse was only infected on the 25th of October, just before its 

 isolation, thirteen days elapsed between the date of its infection 

 and its death. The period between infection and death was 

 experimentally established as from one to two weeks. I could 

 not make these experiments on white mice until I was certain 

 that the epidemic had really disappeared. I therefore waited for 

 some weeks before I commenced with them. 



In the meantime I resolved to make some experiments on 

 other animals, to see whether they were susceptible to the bacillus. 

 My chief interest centred in the Field Vole (Arvicola arvalis), 

 which was obtainable in great abundance in the neighbourhood of 

 Greifswald in November, 1890. Through the kindness of Dr. 

 Ollmann and Dr. Hesse, I was easily enabled to procure plenty 

 of these little animals for experiment. As is well known, Koch 

 has proved that the Field Vole is proof against the minute 

 bacillus of " mouse-septicsemia ; but, on the other hand, I have 

 established the fact that it is extremely susceptible to the bacillus 

 of glanders ; whereas the tame white mouse is proof against it. 

 It therefore appeared doubtful to me whether the Field Vole 

 would be susceptible to the bacillus causing the epidemic amongst 

 white mice. On Nov. 10th I inoculated two Field Voles under 

 the skin of the back with the gelatine culture obtained from the 

 liver of the mouse which had died on Nov. 2nd. One Field Vole 

 was found dead on Nov. 12th. The spleen was large, the liver 

 moist and shining, and the lungs spotted. On making an 

 expressed preparation of the liver, the typical bacilli were found 

 in great abundance. In the gelatine-tubes a thick coating of 

 bacilli was formed. On the same day, Nov. 12th, and imme- 

 diately after the examination, this Field Vole was thrown into a 

 cage amongst three healthy Field Voles, which at once began to 

 gnaw the body. 



