rOle of stomoxys calcitrans. 481 



Careful note was taken at least five times daily of the ap- 

 proximate number of flies biting the diseased animal, horse 

 49. At no time during the six days were there fewer than 100 

 flies biting the horse. On the morning of March 20 there were 

 estimated to be 350 flies either biting or resting on the horse. 

 The horse was in the early stages of the infection from the 

 seventh day to the thirteenth day, and capable of actively resist- 

 ing the attacks of the flies. That the flies did draw blood from 

 the infected host was demonstrated by microscopical examination 

 of the emulsified abdominal contents of several of them at various 

 times during the course of the experiment. Trypanosomes in 

 moderate numbers were found in fresh preparations and in 

 stained smears. 



Horse H-U. — This healthy horse was the first used for ex- 

 posure to the flies possibly contaminated with surra blood. 

 The infected horse was first removed after a bath with cresol to 

 drive off its parasites, and the stall was similarly sprayed thor- 

 oughly with the disinfectant. No. H-4 was not placed in the 

 stall occupied by No. 49, but in the adjoining stall, where by 

 this time the flies had been driven. No. H-4 was exposed for 

 twenty-four hours, during which time it was observed at least 

 five times to be infested by flies to the extent of 10 to 100 flies. 



Horse 269. — Six hours after the removal of No. 49 it was 

 replaced by the second contact. No. 269. The fly infestation had 

 noticeably decreased both within the cage and on the horses. 

 Before the end of twenty-four hours the number of flies had 

 been reduced to a few thousands and the horses received the 

 bites of relatively few, probably not more than 40 per cent, at 

 the close of the period of experimentation. 



Horse H-3. — The two horses in the foregoing experiments 

 were withdrawn, after carefully ridding them of the flies they 

 harbored, and were superseded by No. H-3 which served as host 

 from the twenty-fourth to the forty-eighth hour. The fly in- 

 festation was marked by few bites, never more than 15 at any 

 one time of the five daily observations. 



The cause of the decrease in the number of flies was ascer- 

 tained to be the depredations of four or five voracious lizards 

 which were the survivors of hundreds killed by systematic 

 spraying prior to the introduction of the flies. These lizards 

 were observed to invade the ceiling and walls of the cage, and 

 with characteristic darting movements destroy an astonishing 



