THEORY OF RELAPSES. 645 



of the immune body is established by the fact that 

 passive immunization can be accomplished by the 

 use of serum having no germicidal action. Phago- 

 cytosis is concerned chiefly with organisms killed 

 by the germicidal agent. Marked agglutination 

 occurs with immune serum. 



The immunity conferred by an attack of relaps- 

 ing fever is probably of long duration. Other ani- 

 mals are also immune to a second infection. 



The development of immune bodies which oc- Theory of 

 curs with the first febrile period is insufficient to 

 cause complete destruction of the spirilla. A few 

 of these, aided possibly by their sheltered location 

 in lymph spaces, survive and may become immu- 

 nized to some extent against the antibodies. These 

 organisms by multiplication institute a second 

 febrile period which is followed by a higher devel- 

 opment of immune bodies. Each relapse has the 

 effect of heightening the immunization until com- 

 plete destruction of the organisms occur. 



Hereditary immunity may result from intra- Hereditary 

 uterine infection. Spirilla have been found in ' 

 the heart's blood of the human fetus. Novy and 

 Knapp describe the occurrence of both active 

 hereditary immunity occurring in the young of 

 infected rats and passive hereditary immunity oc- 

 curring in the young of rats passively immunized. 



It is evident from the work of Novy and Knapp 

 that the chief difficulty in the production of a 

 curative serum is that of the cultivation of the 

 spirillum. It may be possible, however, to immu- 

 nize larger animals with infected blood and thus 

 obtain an efficient antiserum. 



