644 INFECTION AND IMMUNITY. 



of the parenchymatous organs, ecchymoses and 

 infarcts of the spleen and kidneys are found in 

 fatal cases. 



Prophylaxis consists in isolation of the patient, 

 cleanliness, and the destruction of vermin, espe- 

 cially bedbugs. 



Relapsing fever occurs in various races of man, 

 and so far as known none is immune. 



immunity. As stated above, a remarkable feature in the 

 course of the disease is the rapidity with which the 

 micro-organisms disappear from the blood at the 

 time of the crisis. Metchnikoff refers this to 

 phagocytosis by the microphages, which undergo 

 a progressive increase during the paroxysm and 

 decrease after the crisis. Very little phagocytosis 

 appears to take place in the circulating blood, but 

 in the spleen many spirochetes are found within 

 polymorphonuclear leucocytes. 



Tictin also found the spirochetes in the paren- 

 chymatous cells of the kidney, liver and lungs. 

 Phagocytosis is most marked at or near the time 

 of the crisis. According to Metchnikoff. relapse 

 or reinfection is accomplished by spirochaete which 

 again invade the body from the spleen. 



According to Novy and Knapp, two distinct 

 types of protecting substances develop during the 

 course )f the disease. They describe a germicidal 

 substance which causes bacteriolysis both in vitro 

 and as observed in Pfeiffer's phenomenon. In ad- 

 dition to this germicidal substance, they believe 

 that a second protecting substance, which they 

 term the immune body, is present. The existence 



