ROLE OF STOMOXYS CALCITRANS. 



483 



hosts and parasites were thus under ready observation and very 

 accurate notes could be obtained. The number of flies biting 

 was noted, and the guinea pigs were left in the cage until the 

 flies were apparently satisfied. 



On the fourth hour of the experiments the presence of the 

 trypanosomes in the feeding flies was demonstrated in several 

 flies taken from the jar. An emulsion of the stomach and 

 intestinal contents showed abundant trypanosomes. These were 

 present on an average of 15 parasites per field, nearly as many 

 as found in the blood of the original host, guinea pig 35. 



The surra guinea pig 35 received its infection through ino- 

 culation of an emulsion of a single specimen of Stomoxys. This 

 fly had been fed flve minutes on a surra guinea pig and six hours 

 later was emulsified and examined microscopically. Numerous 

 surra-like organisms were present prior to inoculation into guinea 

 pig 35. This animal was first positive microscopically five days 

 following injection, and died of surra on the forty-second day. 



The experiment was begun on April 2 with 300 newly emerged 

 Stomoxys calcitrans and heavily infected guinea pig 35. The 

 following table represents the data compiled : 



Table I. — Flies fed on guinea pigs in jar. 



Guinea pig used. 



Time after feeding on 

 infected animal. 



Number 

 of flies 



counted 



on 

 animal. 



Length of 

 time fed. 







225 



155 

 90 

 70 



Hours. 

 3 



6 

 5 



7 



Healthy animal: 



No. 81 



5 minutes to 6 hours 



20 hours to 25 hours 



46 hours to 53 hours 



No. 84 _. 



No. 87 





The three healthy guinea pigs used in this experiment were 

 held in quarantine for a period of forty-five days. They had 

 been examined by the microscope twice to thrice weekly, but in 

 no case were trypanosomes discovered. It was not thought neces- 

 sary to waste animals in proving that the guinea pigs used were 

 susceptible by blood inoculation. Subsequent experiments give 

 sufficient evidence on this point. 



Therefore, it is concluded that under the conditions stated 

 Stomoxys did not convey surra by direct mechanical infection. 



