KELATIONS OF SPIKOCH.ETE TO THE DISEASE 509 



human subject by injecting blood containing the spirochetes, 

 and this experiment has been several times repeated with the 

 same result. Additional proof that the organism is the cause of 

 the disease has been afforded by experiments on 'animals. Carter 

 in 1879 was the first to show that the disease could be readily 

 produced in inonkeys, and his experiments were confirmed by 

 Koch. In such experiments the blood taken from patients and 

 containing the spirochetes was injected subcutaneously. In the 

 disease thus produced there is an incubation period which usually 



Fig. 153.— Spirochete obermeieri in blood of infected mouse. 

 x 1000. 



lasts about three days. At the end of that time the organisms 

 rapidly appear in the blood, and shortly afterwards the tempera- 

 ture quickly rises. The period of pyrexia usually lasts for two 

 or three days, and is followed by a marked crisis. As a rule 

 there is no relapse, but occasionally one of short duration occurs. 1 

 White mice and rats are also susceptible to infection. In the 

 former animals the disease is characterised by several relapses ; 

 in the latter there is, however, no relapse. 



1 Norris, Pappenheimer, and Flournoy, in their experiments on monkeys 

 with the organism of American relapsing fever, found that several relapses 

 occurred. 



