IMMUNITY 497 



experiments the blood taken from patients and containing the 

 spirochaetes was injected subcutaneously. In the disease thus 

 produced there is an incubation period which usually lasts about 

 three days. At the end of that time the organisms rapidly appear 

 in the blood, and shortly afterwards the temperature 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 





1 '!.. 119. Spirochsete Obernieieri in blood of infected mouse. 

 xlOOO. 



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. 



Immunity. Metclmikoff found that during the fever the 

 spirocluL-tes were practically never taken up by the leucocytes in 

 the circulating blood, but that at the time of the crisis, on dis- 

 ;ijipi'jiring from the blood, they accumulated in the spleen and 

 were ingested in large numbers by the microphages or poly- 

 Morris, Pappeuheimer, and Flournoy, in their experiments on monkeys 

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

 occurred. 



