Immunity 553 



covers, the mortality being about 4 per cent. The fatal 

 cases are usually old or already infirm patients. The Indian, 

 African, and American varieties present variations of no great 

 importance. The European fever usually ends after the sec- 

 ond or third relapse, the African not until after a greater 

 number. 



The spirochaeta are present in the blood in great numbers 

 during the febrile stages, but entirely disappear during the 

 intervals: 



Lesions. There are no lesions characteristic of relapsing 

 fever. 



Bacteriologic Diagnosis. This should be quite easily 

 made by an examination of either the fresh or stained 

 blood, provided the blood be secured during a febrile parox- 

 ysm. The readiness with which the organisms take the stain 

 leaves little to be desired. 



Novy and Knapp have found that the serum of recovered 

 cases can be used to assist in making diagnosis because of its 

 agglutinating, germicidal, and immunizing powers. 



Immunity. The phenomena of immunity are vivid and 

 important. At the moment of decline of the fever a power- 

 ful bacteriolytic substance appears in the blood and dis- 

 solves the organisms. At the same time an immunizing 

 substance appears. The two do not appear to be the same. 



The immunizing body affords future protection to the 

 individual for an indefinite length of time. It can be 

 increased by rapidly injecting the animal with blood con- 

 taining spirochaeta. Serum containing the immunizing body 

 imparts passive immunity to other animals into which it is 

 injected, and, according to Novy and Knapp, establishes a 

 solid basis for the prevention and cure of relapsing fever in 

 man. 



