(152) 



STEUCTUEE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 393 



legs and bodies of flies which had been allowed to have access 

 to infected material. Hamilton (1903) recovered Bacillus 

 typhosus five times in eighteen experiments from flies caught 

 in two undrained privies, on the fences of two yards, on the 

 walls of two houses and in the room of an enteric fever 

 patient. A series of careful experiments were made by 

 Sellars 1 in connection with Niven's investigations on the 

 relation of flies to infantile diarrhoea. Out of thirty-one 

 batches of house-flies carefully collected in sterilised traps in 

 several thickly populated districts in Manchester he found, 

 as a result of cultural and inoculatory experiments, that 

 bacteria having microscopical and cultural characters resem- 

 bling those of the Bacillus coli group were present in four 

 instances, but they did not belong to the same kind or 

 variety. Buchanan (1907) was unable to recover the bacilli 

 from flies taken from the enteric ward of the Glasgow Fever 

 Hospital. Flies were allowed to walk over a film of typhoid 

 stool and then transferred to the medium (Griinbaum and 

 Hume's modification of MacConkey's medium), and subse- 

 quently allowed to walk over a second and a third film of 

 medium. Few typhoid bacilli were recovered and none from 

 the second and third films. Sangree (1899) performed 

 somewhat similar experiments to those of Buchanan and re- 

 covered various bacilli in the tracks of the flies. This method 

 of transferring the flies immediately from the infected material 

 to the culture plate is not very satisfactory, as I have already 

 pointed out (1908), as it would be necessary for the flies to 

 be very peculiarly constructed not to carry the bacilli. The 

 fly should be allowed some freedom before it has access to the 

 medium to simulate natural conditions. Experiments of this 

 kind were carried out in the summer of 1907 by Dr. M. B. 

 Arnold (superintendent of the Manchester Fever Hospital) 

 and myself. Flies were allowed to walk over a film of 

 typhoid stool and then were transferred to a wire cage, where 

 they remained for twenty-four hours with the opportunity 



1 Recorded in the ' Report on the Health of the City of Manchester, 

 1906,' by James Niven, pp. 86-96. 



