They conclude that in cities where food is plentiful flies rarely migrate from the locality in which they are bred, and consequently the number of bacteria which they carry depends upon the general 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 demonstrates 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 experiments. Celli (1888) fed flies on pure cultures of _Bacillus typhosus_ and declared 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 4 × 3 × 3 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 isolated _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).