BACTERIA CARRIED BY FLIES 245 



recently little attention has been paid to this matter. Nicoll 

 (1911) has begun such a study with interesting results. He finds 

 that the house-Hy may carry at least twenty-seven varieties of 

 Bacillus coll, by far the most frequent of which are B. coli com- 

 mune and MacConkey's bacillus No. 71. From the character of 

 these colon bacilli it would appear that the house-fly derives its 

 bacterial flora from excremental matter and other sources. The 

 presence of colon bacilli in the digestive tract of the fly is only to 

 be expected from the filthy feeding-habits of the insect; in fact, 

 the absence of these bacilli would be more than remarkable. 

 Nicoll also finds that certain non-lactose fermenting bacilli appear 

 to be capable of multiplying in the intestine of the fly. Of these 

 Morgan's bacillus No. 1 is not an infrequent inhabitant of the fly's 

 intestine and B. 2)Cirati/p}iosHs B. has been found on two occasions. 

 Graham-Smith (1909) has also examined flies captured in 

 various places Avith a view to ascertaining w^hat percentage were 

 infected with bacilli of the colon group. The results of his 

 examinations of flies from the diiferent sources was as follows : 

 from the neighbourhood of decaying animal matter, Cambridge, 

 28 flies were examined and 54*5 per cent, were infected ; from 

 a railway-siding, Islington, 48 flies were examined and 25 per cent, 

 were infected ; from a room used by men at a gas-works, 24 flies 

 were examined and 16"6 per cent, were infected; from a house 

 near a glue works, 26 flies were examined and 15 per cent, were 

 infected ; from the kitchen of a London County School, 18 flies 

 w^ere examined and 22'2 per cent, were infected ; from a house 

 about fifty yards distant from a jam factory, Bermondsey, 40 flies 

 were examined and 10 per cent, were infected. The flies which 

 were examined were M. domestica, Fannia canicidaris, Calliphora 

 ej^ythrocephala and G. vomitoria, Stomoxys calcit7^ans and a few 

 other small flies. Cultures were made of both the intestines and 

 of the surfaces of the flies' bodies. Altogether 35 lactose- 

 fermenting organisms of the colon group were isolated, 22 from 

 surface cultures and 13 from the intestines. Although the 

 numbers were comparatively small, the experiments indicated 

 that the flies were infected with bacilli of the colon group in 

 proportion to the opportunities offered by the locality they were 

 frequenting. The highest degree of infection was found on those 



