AFRICAN TICK FEVER 515 



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

 they came to the conclusion that the spirochsetes were not simply 

 carried mechanically by the ticks, but probably underwent some 

 cycle of development in the tissues of the latter. Leishman has 

 since shown that the ticks of the second generation may also be 

 infectious. The species of tick concerned is the ornithodorus 

 moubata. These results were confirmed 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 stomach of the insect. 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. : He also traced the presence of the 

 spirochsetes in the eggs laid by the infected ticks, and in the 

 young embryos hatched from them. On the other hand, Leish- 

 man has failed to find any evidence of spirochsetes in the tissues 

 of ticks later than ten days after ingestion of blood containing 

 them, or in the ova laid by them, or in the young ticks when 

 hatched, though these were proved by experiment to be infective. 

 After ingestion of the blood by the ticks, he found that morpho- 

 logical changes occurred in the spirochaetes, resulting in the 

 formation of minute chromatin granules which traverse the 

 walls of the intestine and are taken up by the cells of the 

 Malpighian tubules ; they also penetrate the ovaries and may 

 be found in large numbers within the ova. Similar granules are 

 to be seen in the Malpighian tubules of the embryo ticks, where 

 they are also found in the subsequent stages of their life. He 

 has proved that infection of animals may be produced by inocu- 

 lation with crushed material containing the granules but no 

 spirochsetes. He accordingly considers that the granules in 

 question represent a phase in the life-history of the parasite, and 

 that infection occurs by inoculation of the skin with the chromatin 

 granules voided in the Malpighian secretion and not by unaltered 

 spirochsetes from the salivary glands. A similar view is taken 

 by Hindle, who has found that when infected ticks, in which 

 the spirochsetes have disappeared, are heated to a temperature of 

 35 C., the spirochsetes reappear in the organs and ccelomic 

 fluid. It is also interesting to note that Balfour has found 

 similar granules in ticks (argas persicus) infected with spirochcete 

 gallinarum, and he has also observed the formation of granules 

 from spirochsetes in the blood of Sudanese fowls treated with 

 salvarsan. 



Koch also made extensive observations on the ticks in Ger- 

 man East Africa, and found that of over six hundred examined 



