PROTOCOLS OF EXPERIMENTS 77 



Result: Guinea-pig 26, inoculated with the viscera of ricket- 

 tsia-free louse W 262, after an incubation period of sixteen 

 days, developed temperatures consistent with typhus. Al- 

 though it was not killed until the fifth day of temperature, no 

 lesions were found in the brain. One of three guinea-pigs, 

 No. 72, which survived inoculation from this guinea-pig, failed 

 to develop typhus during an observation period of twenty-two 

 days, at the end of which time it was inoculated with blood 

 from a typhus patient. No temperature suggestive of typhus 

 developed in a further observation period of nineteen days. 



Discussion: Guinea-pig 26 developed a course of fever con- 

 sistent with typhus, though after an incubation period of un- 

 usual length, following louse injections. The failure to find 

 lesions in the brain of this guinea-pig, and that of No. 73 in- 

 oculated from it, is strong evidence against typhus. In no 

 instance in a series of thirty-six consecutive brains examined 

 of guinea-pigs infected with typhus with blood, human and 

 guinea-pig, were the brain lesions absent and we are inclined to 

 accept the absence of brain lesions in guinea-pigs 26 and 73 as 

 proof of the absence of typhus. The failure of guinea-pig 72 to 

 develop typhus following inoculation from No. 26 is offset by 

 its failure to react to the inoculation with the blood of patient 

 814. 



Conclusion: Rickettsia-free louse W 262 probably did not 

 contain the virus of typhus. 



