355 



0.31 in thickness. The relapsing fever in which it occurs has 

 been observed in South America. Noguchi has obtained cul- 

 tures by the same methods as he employed for Sp. rossii, but the 

 cultivation is more difficult. 



Several other varieties of spirochetes, which cause relapsing 

 fever in man, have been recognized. The spirochete concerned 

 in any case seems to be able to infect several species of insects and 



^^P^^' 



FIG. 141. Spirochczta recurrentis (novyi). Organisms of different lengths in the 

 blood of a white rat. X 1500. (After Novy and Knapp.) 



to be transmitted to a new mammalian host by them. Further- 

 more one species of insect seems to be capable of transmitting 

 any one of these spirochetes. 1 



The diagnosis of relapsing fever depends upon recognizing the 

 characteristic spirochetes in the blood during the febrile attack. 

 Their recognition offers little difficulty, as a rule, but they may be 

 overlooked by a beginner. In doubtful cases it is well to search 



1 Nuttall: Johns Hopkins Bull, 1913, Vol. XXIV, pp. 33-39. 



