ROLE OF STOMOXYS CALCITRANS. 515 



GENERAL SUMMARY. 



1. Only negative results were obtained in the attempts at 

 direct mechanical transmission of surra with flies which were 

 induced to bite healthy animals at intervals ranging from five 

 minutes to three days after being permitted to complete the 

 feeding upon infected animals. Thousands of Stomoxys calci- 

 trans were employed in 29 experiments involving the use of 

 3 horses, 6 monkeys, and 22 guinea pigs. 



2. Twenty-seven experiments were performed in attempts to 

 transmit surra by the interruped method of feeding. All at- 

 tempts proved negative where a single application of a varying 

 number of flies was used, as many as 38 on a horse, and a maxi- 

 mum of 40 on a small guinea pig. The intervals between feeding 

 on infected and healthy animals averaged twenty-five to forty 

 seconds in the two instances cited. 



3. In 3 trials, interrupted feeding was employed in successive 

 daily applications. In attempting to determine the minimum 

 number of bites necessary to infect an animal, as high as 40 

 were followed by negative results. The only positive result 

 obtained was produced from a succession of 206 interrupted bites 

 in which the flies were transferred immediately from the infected 

 to the clean animal. The flies were applied thirty-two hours 

 during a period of six days. 



4. The results of these experiments indicate that Trypano- 

 soma evansi does not develop in the body of Stomoxys calcitrans. 

 Ninety-four days was the longest period in which laboratory-bred 

 flies were tested for a cyclical development, and sixty-seven days 

 the maximum for wild flies. 



5. Organisms of surra were not found in Stomoxys calcitrans 

 beyond eighteen hours after feeding on an infected animal, ana 

 the limit for infection by inoculation was ascertained in these 

 experiments to be six hours. 



6. Pathogenic trypanosomes were found in the proboscis of 

 the fly thirty seconds after feeding on infected blood. Within 

 one minute and thirty seconds the organisms were not present 

 in the mouth parts in a form capable of infecting by inoculation 

 into guinea pigs. 



7. The wounds made by the labium of Stomoxys were not 

 found to be a suitable channel for infection. Consequently it 

 is not likely that surra in domestic animals is produced through 

 this avenue by external contamination; namely, fseces, mouth 

 parts, and pulvilli of infected flies. 



