RELAPSING FEVER 195 



central part staining least. Some observers have de- 

 scribed a delicate terminal flagellum ; the presence of 

 flagella is denied by most authorities. A striking feature 

 of the organism is its extraordinary motility, which is 

 progressive as well as rotary and lateral. It is best 

 stained by aniline dyes, especially by some modification 

 of Romanowsky's stain, and also by carbol-fuchsin and 

 gentian violet. It is decolorized by Gram's method. 



When faintly stained by Romanowsky's method the 

 parasite is blue, if the staining is prolonged it becomes 

 red. All attempts to cultivate it have failed, but it can 

 be kept alive in citrated blood outside the body for 

 several days. Tictin found the spirillum in bugs fed 

 upon patients suffering from relapsing fever and showed 

 that they could survive in them for seventy-seven hours. 

 He also succeeded in infecting monkeys with the fluids of 

 such bugs crushed immediately after feeding, but when 

 bugs had been killed forty-eight hours after feeding their 

 fluids were not infective, although the S. obermeieri 

 could be found in stained preparations. Karl in sky, in 

 infected houses, found the spirillum in bugs, and that the 

 spirilla could live in these for thirty-nine days. Nuttall 

 has recorded the infection of one mouse from another 

 through the medium of a bug which was fed first on the 

 infected animal and then allowed to bite the uninfected 

 mouse. 



Blood containing the spirillum has been frequently 

 inoculated into man, both deliberately and by accident, 

 and has caused relapsing fever. Various kinds of 

 monkeys have also been successfully inoculated. Until 

 recently man and monkeys were considered to be the 

 only susceptible animals, but Novy and Knapp have 

 recorded the successful inoculation of white mice in 

 which relapses occurred, and of white rats after a pre- 

 liminary passage through a monkey. 



The incubation period following inoculation in man 

 is usually between thirty and thirty-six hours. 



There has been a good deal of speculation as to the 



