ROLE OF STOMOXYS CALCITRANS. 497 



The possibility of infection being carried by the fly's pulvillus 

 was tested by using flies {Musca domestica) , not bloodsuckers, 

 whose pulvilli were as large as, or larger than, those of Stomoxys. 

 Both monkeys and guinea pigs were used in these tests. The 

 tests were made more conclusive by using large numbers of flies 

 in bottles applied to the monkeys and a smaller number in large 

 glass tubes on guinea pigs. 



In the first of the monkey experiments, 30 laboratory-bred 

 Stomoxys were applied to the tail of the healthy animal im- 

 mediately followed by 50 flies (Musca) from a separate bottle, 

 which previously had been applied to the abraded tail of a surra 

 monkey. Twenty minutes were allowed the Musca to carry the 

 infected contents of feet and mouth parts into wounds left by 

 the clean Stomoxys. In the other experiment with the monkey, 

 200 Stomoxys and 250 Musca were employed. The 3 guinea-pig 

 experiments were performed in a similar way with fewer flies. 



All 5 experiments resulted negatively, the animals being used 

 later for other purposes. One of the guinea pigs subsequently 

 reacted to an inoculation of infected blood. 



THE RELATION OF NONBITING FLIES TO STOMOXYS IN CON- 

 TAMINATIVE INFECTIONS. 



In considering the relations existing among flies of the family 

 Muscidse and their parasitism, a peculiar phase is brought to 

 light. I was curious to learn why such an abnormal percentage 

 of nonbiting flies was generally found in collecting insects from 

 domestic animals. In an examination of extensive collections 

 made with a net swung over the backs of the animals, the ma- 

 jority of the nonbiting flies were found to contain blood-engorged 

 abdomens. These when dissected and examined microscopically 

 showed mammalian blood to be the principal food constituent. 



A quiet bullock was selected for closer observation. Some 

 150 to 200 flies, mostly muscids, were seen to collect on him. 

 Many hundreds of dung flies, including house flies, were scattered 

 about on the floor of the stall, and an occasional one of these was 

 seen to join the others on the host's body. 



In a short while my attention was attracted to the peculiar 

 grouping of the ectoparasites; groups of 2 to 4 and 5 prevailed. 

 On closer inspection the group was found invariably to consist of 

 more than one species, a Stomoxys usually providing the central 

 figure. Where this species was lacking it was found that the 

 group fed from a common area with the heads of the individuals 

 in close contact. The food of the latter was found to be a 



