The House-fly as a Carrier of Disease 153 



standard of cleanliness in that locality. Flies caught in a street of 

 modern, fairly high class, workmen's dwellings forming a sanitary 

 oasis in the midst of a slum area, carried far less bacteria than those 

 caught in the adjacent neighborhood. 



Thus, as the amount of dirt carried by flies in any particular 

 locality, measured in the terms of bacteria, bears a definite relation 

 to the habits of the people and to the state of the streets, it demon- 

 strates the necessity of efficient municipal and domestic cleanliness, 

 if the food of the inhabitants is to escape pollution, not only with 

 harmless but also with occasional pathogenic bacteria. 



The above cited work is of a general nature, but, especially in 

 recent years, many attempts have been made to determine more 

 specifically the ability of flies to transmit pathogenic organisms. 

 The critical reviews of Nuttall and Jepson (1909), Howard (1911), 

 and Graham-Smith (1913) should be consulted by the student of 

 the subject. We can only cite here a few of the more striking experi- 

 ments. 



Celli (1888) fed flies on pure cultures of Bacillus typhosus and de- 

 clared that he was able to recover these organisms from the intestinal 

 contents and excrement. 



Firth and Horrocks (1902), cited by Nuttall and Jepson, "kept 

 Musca domestica (also bluebottles) in a large box measuring 4x3x3 

 feet, with one side made -of glass. They were fed on material 

 contaminated with cultures of B. typhosus. Agar plates, litmus, 

 glucose broth and a sheet of clean paper were at the same time 

 exposed in the box. After a few days the plates and broth were 

 removed and incubated with a positive result." Graham-Smith 

 (1910) "carried out experiments with large numbers of flies kept 

 in gauze cages and fed for eight hours on emulsions of B. typhosus 

 in syrup. After that time the infested syrup was removed and the 

 flies were fed on plain syrup. B. typhosus was isolated up to 48 

 hours (but not later) from emulsions of their feces and from plates 

 over which they walked." 



Several other workers, notably Hamilton (1903), Ficker (1903), 

 Bertarelli (1910) Faichnie (1909), and Cochrane (1912), have iso- 

 lated B. typhosus from "wild" flies, naturally infected. The papers 

 of Faichnie and of Cochrane we have not seen, but they are quoted 

 in extenso by Graham-Smith (1913). 



On the whole, the evidence is conclusive that typhoid germs not 

 only may be accidentally carried on the bodies of house-flies but 



