SPIROCHETE GROUP 445 



acterized by pains in the head and back and by high fever. This 

 is followed by a complete apparent recovery. A second attack, or 

 relapse, occurs usually in about a week, then a third, and even 

 more. The relapses tend to decrease in intensity. The spiro- 

 chetes are to be found in large numbers during the relapses, though 

 usually in diminished numbers. 



Immunity. No specific toxin has been demonstrated. An 

 attack of the disease confers an active immunity. Repeated in- 

 jections of blood containing spirochetes result, in the rat, in the 





v 



Fig. 196. Spirochceta ooermeieri from the blood of a rat (Novy and Knapp 

 in "Journal of Infectious Diseases").' 



development of a hyperimmunity. Immune and hyperimmune 

 blood may be used in conferring a passive immunity. The agen- 

 cies responsible for the development of immunity are not well 

 understood. 



Bacteriological Diagnosis. The organism may be found in 

 fresh preparation or in stained mounts of the blood during a 

 paroxysm. 



Transmission. The disease is supposed to be transmitted by 

 the bite of an infected bed-bug (Acanthia lectularia) , possibly by 



