DUEATION OF INFECTIVE POWEE OF TSETSE. 275 



establish the part, if any, that the wild animals play in the 

 dissemination of this disease, and as my woz'king hypothesis at 

 present is that some species of animals living in the Fly Country 

 harbour the Nagana parasite in their blood, and that the Tsetse- 

 fly carries the infection from affected to healthy animals, much in 

 the same way as the vaccinating needle carries the infection of 

 vaccinia from child to child, it will evidently further this object, 

 if it can be discovered how long the Tsetse-ily retains its infective 

 power. In passing through Fly Country of course it is possible 

 that a Tsetse-fly may be feeding on a wild animal one minute 

 and the next have transferred itself to the horse, ox, or dog ; but 

 if it can be proved to retain the power of infection say for 

 twenty-four hours, the fly's power to do harm is evidently much 

 widened " (p. 6). 



Details, with one chart, are then given of three experiments 

 on native dogs, in which various numbers of Tsetse-flies, from six 

 to twelve, were repeatedly fed on the subject of the experiment, 

 twelve, twenty-four, and forty-eight hours respectively after 

 feeding on an affected animal. The results were that hjematozoa 

 were found in the blood of the dog on the 37th clay, with the 

 twelve-hour interval ; on the 38th day, with the twenty-four 

 hour interval ; and on the 32nd day, with the forty -eight hour 

 interval ; reckoning in each case from the date of the commence- 

 ment of the experiment. 



" (d.) How long does the blood of an affected animal remain 

 capable of giving rise to the disease in a dried condition 1 



" This point may be approached from another direction and 

 some control placed on the results. Instead of using the proboscis 

 of the Tsetse as the conveying instrument, let us use short pieces 

 of thread dipped in blood containing the hematozoa, dried, and 

 at varying periods of time threaded, by means of a needle, under 

 the skin of healthy dogs " (p. 8). 



Details, with charts, are given of seven experiments in which 

 this procedure was carried out with varying results, as to which 

 the author writes (p. 10) ; "These experiments would go to show 

 that the blood of animals affected by Fly Disease retains its 

 capability of ti-ansmitting the disease in a dried condition for 

 twenty -four hours, but that this is exceptional, and that at the 

 end of forty-eight hours the blood is inert. 



"But as the proboscis of the Tsetse may retain blood in a 

 moist condition, it will be interesting to show how long the blood 

 itself, taken aseptically and preserved by suitable means from 

 putrefaction, will retain this infective power. 



" (e.) How long does the blood of an affected animal remain 

 capable of giving rise to the disease if kept in its naturally moist 

 condition 1 " 



