444 



AFRICAN TICK FEVER 



unless in patients debilitated by other causes. The spirilla are 

 considerably fewer in the blood than in the European relapsing 

 fever, and sometimes a careful search may be necessary before they 

 are found. Morphologically they are said to be practically 

 identical, although Koch thought that the organisms in tick 

 fever tended on the whole to be slightly longer ; the average 

 length may be said to be 15 to 35 /x. Dutton and Todd showed 

 that it was possible to transmit the disease to certain monkeys 



. /* 



FIG. 151. Film of human blood containing spirillum of tick fever, x 1000. * 



(cercopitheci) by means of ticks which had been allowed to bite 

 patients suffering from the disease, the symptoms in these 

 animals appearing about five days after inoculation. The disease 

 thus produced is characterised by several relapses, and often 

 leads to a fatal result. In one case they produced the disease 

 by means of young ticks hatched from the eggs of ticks which 

 had been allowed to suck the blood of fever patients, and they 

 came to the conclusion that the spirilla were not simply carried 

 mechanically by the ticks, but probably underwent some cycle of 



1 We are indebted to Colonel Leishman, R.A.M.C., for the preparations 

 from which Figs. 150-152 were taken. 



