v PLAGUE IN THE RAT 115 



lung showed no perceptible change ; the heart's blood 

 did not contain bacilli. 



Experiment 3. — One rat, 1b, was injected cutaneously 

 with a fair dose (several drops being well rubbed into 

 scarifications of the skin at the root of the tail) of 

 sanguineous turbid juice (crowded with B. pestis) from 

 the bubo of rat 1a. This rat was found dead on the 

 fourth day. Post mortem : — Hemorrhagic inguinal bubo 

 on the side corresponding to the site of the cutaneous 

 inoculation. The juice of this bubo was crowded with 

 short (bipolar) B. pestis. Spleen not enlarged, no 

 bacilli ; heart's blood no bacilli ; other viscera showed 

 no noticeable change. The culture of material from the 

 bubo produced translucent growth on gelatine, the bacilli 

 very short. 



Experiment 4. — One rat, lc, was inoculated cutaneously 

 with a good-sized loop of a subculture on agar of the 

 above bubo of rat 1b. The animal was found dead on 

 the fourth day. The inguinal gland corresponding to 

 the side of inoculation was found enlarged, and contained 

 numerous short B. pestis ; most of them in a state of 

 degeneration (granular), some swollen up into spherical 

 masses. The spleen was slightly enlarged and contained 

 a fair number of B. pestis, showing bipolar staining. 

 Heart's blood no bacilli. 



From this series of experiments it appears that 

 typical virulent B. pestis (L.P. I.) by passage through 

 a Haffkine protected rat had distinctly become attenuated 

 in virulence when employed, whether as bubo juice or as 

 culture therefrom, in the inoculation of a succession of 

 rats. Under ordinary conditions, be it remembered, the 

 most virulent material available is the juice of the bubo 



