AFRICAN TICK FEVER 445 



development in the tissues of the latter. The species of tick 

 concerned is the ornithodorus moubata. These results were con- 

 firmed and extended by Koch. He found that after the ticks 

 had been allowed to suck the blood containing the organisms, 

 these could be found for a day or two in the stomachs of the 

 insects. After this time they gradually disappeared from the 

 stomach, but were detected in large numbers in the ovaries of 

 the female ticks, where they sometimes formed felted masses. 



FIG. 152. Spirillum of human tick fever (Spirillum Duttoni) in blood of 

 infected mouse. x 1000. 



He also traced the presence of the spirilla in the eggs laid by the 

 infected ticks, and in the young embryos hatched from them. 

 He was thus able to demonstrate how the infection might be 

 continued within the tissues of ticks from generation to 

 generation ; in the process of transmission, however, the spirillar 

 form was always observed, and there was no evidence that the 

 organism went through a cycle of change. Koch also made 

 extensive observations on the ticks in German East Africa, and 

 found that of over six hundred examined 11 ,per cent of these 

 insects along the main caravan routes contained spirilla, and 

 in some localities almost half of the ticks were infected. In 



