SPOTTED FEVER. 723 



1907, In order to ascertain the probable source 

 of the virus as occurring in the tick, Eicketts 

 showed that ground squirrels, rock squirrels, chip- 

 munks and ground-hogs were susceptible to the 

 disease. 



Eicketts concludes as follows as to the mainte- Maintenance. 

 nance of spotted fever: "In accordance with the 

 results and deductions which have been outlined, 

 it is conceived that spotted fever is maintained as 

 follows : A certain percentage of the female ticks 

 which have acquired the disease as a consequence 

 of feeding on animals, the latter having been in- 

 fected by other ticks, transmit the disease to their 

 offspring through the egg. The new generation, 

 during the process of feeding, transfer the virus 

 to certain of the susceptible small wild animals 

 (ground squirrels, rock squirrels, chipmunks, 

 ground hogs, and perhaps others), and this may 

 take place during either the larval, nymphal or 

 adult stage, hence at various times of the year. 

 During the infection of the wild animal it is re- 

 quired that hitherto normal ticks, either as larvae, 

 nymphs or adults, acquire the disease by feeding 

 simultaneously with, or shortly after, the feeding 

 of the infected ticks. Begardless of the tick's 

 stage of development at the time it acquired the 

 disease, the virus is retained into the adult period, 

 and in certain of the females reaches the germ 

 cells and again appears in the next generation. 

 The infection of man is an unessential incident 

 for maintenance, and depends on the occasional 

 and accidental bite of the infected adult tick." 



The virus of spotted fever is not filterable 

 through Berkefeld candles. The eggs of infec- 



