40 The Philippine Journal of Science wis 



pharynx kept up a constant titilation. At no time was the labium 

 held still, but there was a continual piston-like movement. The 

 fly bit for twelve minutes and forty seconds, defecating at 

 intervals of from thirty to forty seconds, and at each deposition 

 the fluid voided was bloody. The flrst evacuation took place syn- 

 chronously with the first dilatation of the abdomen. 



The termination of the biting was followed by a quick with- 

 drawal of the labium to its middle, then the rest was slowly 

 withdrawn and cleaned on the fore tarsi. A blood drop flowed 

 to the surface of the skin at the site of feeding. No pain was 

 felt when the labium was withdrawn. All of the bites occurred 

 in an area of 3 centimeters on the fleshy part of the left forearm. 

 I do not attempt to explain why these parasites showed such a 

 marked predilection for a restricted area of my arm. The 

 same phenomenon occurred again subsequently. 



Stomoxys calcitrans appears to attack all animals with equal 

 avidity. Sick animals especially are marked for their attacks. 

 It has been observed by many investigators that infected animals, 

 particularly horses, are more susceptible to the attacks of 

 Stomoxys than are healthy horses. During an outbreak of surra, 

 two years ago, it was noticed in a public corral that 3 horses 

 among a large number of work animals contracted surra, prob- 

 ably several days before the malady was diagnosed. The atten- 

 tion of the veterinarian in charge was attracted, primarily, not 

 by the clinical symptoms, but by the large number of biting flies 

 present on one of the sick animals. This horse did not attempt 

 to dislodge the parasites, the flies feeding until engorged, then 

 flying to the nearest fence to rest. Three horses were examined 

 for blood parasites, and many trypanosomes were found. The 

 weakest horse showed the greatest number, and concomitantly 

 the predominance of the ectoparasites. Incidentally, when the 3 

 sick horses were removed, the infection among the remainder of 

 the animals was checked. 



Experimentally Stomoxys will feed on any animal off'ered for 

 this purpose. Twenty-four specimens of Stomoxys calcitrans 

 were taken while observed in the act of biting a horse. They 

 were placed in 24 glass tubes and applied each day, as long as 

 they survived, to a difl'erent species of animal. In every instance 

 the flies bit and fed upon the blood of the animal on which they 

 were placed. The following table shows the number of flies 

 which survived after each meal and the average number of 

 minutes each fly fed on the various hosts. 



