Fluctuations of Virulence 



25 



other 9 c.c. of 20 per cent, chocolate broth culture plus 1 c.c. of 

 pleural exudate of rabbit dead of intratracheal inoculation. A 

 blood culture was taken on one of the rabbits 6 hours after 

 inoculation and was positive. At autopsy cultures of the heart's 

 blood of both were positive. Of the three that did not die, one 

 received only 2 c.c. of broth culture, one received 20 c.c. of broth 

 culture inoculated with the organism after a week's growth on 

 chocolate agar, and the third, who received the same dose as one 

 that died, had previously received two small inoculations into 

 the stomach. The two animals that died showed increased 

 respiration and high temperatures almost immediately. The 

 mechanism of death in these cases has not been worked out and 

 at present is not clear. 



II. After carrying out the above experiments, we next worked 

 with other strains. About three weeks later, we returned to our 

 meningeal strain "M," but, as the strain we had passed through 

 the animals in our previous experiments had died out, we had to 

 go back to the original strain in rabbit's blood, w T hich then had 

 been out of the body 18 weeks, instead of 10 weeks, as in our 

 first series of experiments. To our surprise, we could not repeat 

 our former experiments as the virulence of the organism had 

 diminished to such a degree. Our results were as follows : 



1. Intratracheal. Three rabbits were injected with 3.5 c.c, 4 

 c.c, and 4 c.c. of 20 per cent, growth in chocolate broth, respec- 

 tively, and one with 2 c.c of the peritoneal exudate of a guinea 

 pig dead from an inoculation. None of these animals died, or 

 even were sick. 



2. Intracerebral. One animal was inoculated with 0.1 c.c. of 

 heavy emulsion of a culture on a chocolate agar slant; it died in 

 48 hours; at autopsy the heart's blood and brain was positive 

 for B. influenzae, but blood cultures 6 hours after inoculation 

 and 24 hours later were negative. The other animal received 0.1 

 c.c. of an emulsion of the brain of the first rabbit; it did not die, 

 nor was it sick. 



3. By stomach tube. One animal was given 20 c.c. of a 20 

 hour growth inoculated with the blood by one rabbit dead with 

 a septicaemia following an intraperitoneal injection. It never 

 showed any reaction. The other animal received 18 c.c of a 20 

 hour chocolate broth culture plus 2 c.c of the peritoneal exudate 

 of a guinea pig dead from an intraperitoneal inoculation. 



