724 INFECTION AND IMMUNITY. 



tious ticks were found by Bicketts to contain a 

 large number of small polar staining bacilli. 

 These organisms were agglutinated in high dilu- 

 tion by the serum of spotted fever cases, but are 

 also found in the eggs of non-virulent ticks. At- 

 tempts at cultivation by Bicketts and Heinemann 

 have been negative. 



immunity. ^" authoritative report of a second attack of 

 spotted fever is on record. According to Bicketts 

 and Gomez, an attack of spotted fever in the 

 guinea-pig and monkey produces a strong active 

 immunity of long duration. This immunity is 

 characterized by the presence of protective anti- 

 bodies in the serum which may be demonstrated 

 by injecting mixtures of virus and immune serum. 

 The concentration of the antibodies in the blood 

 of the immune animal undergoes a decrease in the 

 course of several weeks. 



The female that has recovered from spotted 

 fever transmits immunity to her young. The 

 young are immune even when the female acquired 

 her immunity several months before impregna- 

 tion. The immunity of the young does not de- 

 pend on the ingestion of milk from the immune 

 mother. The character of the inherited immunity 

 has not yet been determined, although it is pre- 

 sumptively a passive immunity that differs from 

 the passive immunity conferred by the injection 

 of immune serum by its longer duration. The 

 long duration of the inherited immunity may 

 depend on the longer time required for the elimi- 

 nation of large quantities of protective substances. 

 Passive immunity may be established in the 

 healthy guinea-pig by the injection of blood or 



