866 



PATHOGENIC MICROORGANISMS 



between the two. Animal experiments made with the African or- 

 ganism, furthermore, usually show a much more severe infection 

 than do similar inoculations with the European variety. The spiro- 

 chaete found in the African disease is usually spoken of at present 

 as ' ' Spirochaeta Duttoni." Novy and Knapp, 48 . after extensive 

 studies with the microorganisms from various sources, have come 

 to the conclusion that, although closely related, definite species 

 differences exist between the two types mentioned above, and that 

 these again are definitely distinguished from similar organisms 

 described by Turnbull 49 as occurring in a similar disease observed 

 in India. 



The mode of transmission of this disease is not clear for all types. 



: : 



FIG. 96.-^SpiROCHvETE OF DUTTON, AFRICAN TICK FEVER. (From preparation 

 furnished by Dr. G. N. Calkins.) 



Dutton and Todd, however, were able to show satisfactorily that, 

 in the case of the African disease at least, transmission occurs 

 through the intermediation of a species of tick. The conditions 

 under which such intermediation occurs have been carefully studied 

 by Koch. 50 The tick (Ornithodorus moubata) infects itself when 

 sucking blood from an infected human being. The spirochaete may 

 remain alive and demonstrable within the body of the tick for 

 as long as three days. Koch has shown, furthermore, that they 

 may be found also within the eggs laid by an infected female tick. 

 He succeeded in producing experimental infection in monkeys by 



48 Novy and Knapp, loc. cit. 

 "Turnlm!!, Indian Mcd. Gaz., 1905. 

 50 Koch, Berl. med. Woch., 1906. 



