107 



confined to one species or family. These agents have not, however, led 

 to the establishment of trypanosomiasis in areas away from the fly- 

 belts, and in no instance so far recorded in Southern Rhodesia can 

 Glossina be definitely disassociated from the inception of an outbreak. 



In the following year (1918) Jack (72) again expressed his conviction 

 that the infection of cattle with trypanosomiasis in the absence of 

 Tsetse-fly is of frequent occurrence in Rhodesia, and urged that the 

 greatest care should be taken not to allow infected cattle to come into 

 contact with healthy herds, especially during the spring and summsr 

 months. 



In 1919 Jack stated (74) that, though direct experimental proof was 

 still lacking, the evidence that in Southern Rhodesia Trypanosoma 

 pecorum is commonly spread among domestic animals in the absence of 

 Glossina had still further accumulated. 



Other testimony to the same effect, likewise relating to Rhodesia has 

 been brought forward by Hornby (63), who mentions a case in which 

 1,000 village cattle, examined just at the commencement of the rains, 

 showed less than a dozen cases of infection. Six months later, in the 

 same village, 500 of the cattle previously examined were found to be 

 either dead or very ill from trypanosomiasis. On neither occasion was 

 a Tsetse-fly seen in the vicinity, although occasional individuals were 

 observed in neighbouring areas. The author thinks this seasonal 

 occurrence of the disease, which is coincident with that of biting flies 

 other than Glossina, to be significant, when it is considered that out of 

 300 cattle kept for one month in a thin fly-belt, only 20 animals became 

 infected. He adds, further, that on estates where the danger from 

 mechanical infection was realised, and measures were taken to isolate 

 all infected animals, no fresh cases occurred during the following rainy 

 season, although severe outbreaks had previously been the rule. It 

 .should be stated that, in an annotation to Hornby's paper, the Chief 

 Veterinary Surgeon, while admitting that in some areas trypanosomiasis 

 in domestic animals may be transmitted by flies other than Tsetse, re- 

 marks that he believes such cases to be very rare in Southern Rhodesia. 



In 1917 Chambers (28), while recording no fresh evidence of his own, 

 summarised the observations and experiments of a number of authors 

 Avho have reported outbreaks of cattle trypanosomiasis in Northern 

 Rhodesia and adjoining territories, in areas definitely known to be free 

 from Tsetse-flies. 



Quite recently (November, 1921) Dry (450) has given details of an 

 outbreak of trypanosomiasis in cattle on a farm in the Kericho district, 

 Kenya Colony, under circumstances pointing to species of Stom'oxys 

 as being the probable transmitters. The only other blood-sucking flies 

 found on and in the vicinity of the farm, the altitude of which is about 

 6,300 ft., belonged to the genus Haematopota (Tabanidae). No 

 Tsetse-flies were met with, and there were no records of any having 

 been observed in the neighbourhood. 



It is clear that the whole question calls for careful experiment and 

 investigation. 



CHAPTER XI 

 THE EFFECT OF EXTERNAL FACTORS UPON TSETSE-FLIES. 



Great interest attaches to the study of the influence of external 

 factors upon the duration of life of Tsetse-flies, since it may suggest 

 means for the destruction of these insects. In particular, it has been 

 observed that G. palpalis, more than any other insect, is easily killed 



