Pathogenicity. 807 



The infection fs ti^nsmitted by the so-called tsetse fly, 

 which somewhat resembles the house fly although it is some- 

 what larger, principally by the glossina morsitans (Fig. 142), 

 in such a way that it sucks blood from the infected animal, and 

 then carries the parasites into the body by its bite. Freshly 

 molted flies are harmless, if however they have alighted upon 

 an affected animal only a single time they may transmit the 

 disease and trypanosomes may be demonstrated in their pro- 

 boscis and stomach shortly after sucking the blood. By the 

 transportation of affected flies the disease was successfully 

 produced in previously non-infected localities, while on the 

 other hand animals driven during the day in infected localities 

 became affected even when they had not partaken of food nor 

 water while en route. Furthermore, the extension of the in- 

 fected territory corresponds accurately with the geographical 

 distribution of the tsetse fly (between the 10th deg. north, and 

 30 deg. south latitude), where its appearance in great numbers 

 is usually followed by severe outbreaks. 



Fig. 142. Glossina morsitans. A with closed, B with spread wings, anterior 

 part in profile. A and B enlarged 2.5 tiifies. (After Bruce.) 



Where affected animals are present or those which have 

 passed through the disease within a short time, the fly is 

 afforded ample opportunity for taking up trypanosomes ; flies 

 may also obtain the infectious material from wild animals 

 (buffaloes, antelopes, hyenas, zebras and quaggas), in the blood 

 of which it may occur as a harmless parasite. The tsetse fol- 

 lows these animals everywhere; with the appearance of the 

 summer season the infectious material is then taken from them 

 by the young flies, and transmitted to domestic animals, while 

 with the eradication of the game the tsetse fly also disappears, 

 so that infected territories may thus become free. 



According to Koch's experience in western and northern Africa, 

 where the glossina morsitans is unknown, the disease is transmitted by 

 the closely related Gl. fusca. According to Brumpt the Gl. pallidipes, 



