During the past decade much has been published in regard to the supposed danger from house flies as the disseminators of pathogenic bacteria. More or less evidence has been presented to the effect that these insects may, at times, spread a long category of infections, including, to quote the list of Purdy1 (see also Hewitt2), typhoid fever, infantile diarrhea, bacillary dysentery, cholera, tuberculosis, diphtheria, erysipelas, contagious ophthalmia, cerebrospinal meningitis, anthrax, and possibly smallpox. This evidence has recently been summarized and discussed by Chapin3 in an interesting manner. For a number of these diseases the chain of evidence is incomplete, but for infections of fecal origin, the guilt of this ubiquitous insect has been clearly estabhshed in certain instances, especially as regards typhoid fever. Hamilton,4 Ficker,5 Klein,6 and Bertarelli7 have severally succeeded in isolating the typhoid bacillus from flies caught in the neighborhood of typhoid fever cases, although the attempts of other investigators under similar circumstances have been fruitless. Hamilton, first, in 1903, was able to prove that an outbreak of typhoid fever, restricted to a certain ward of Chicago where the street sewers were inadequate and the sanitary arrangements of most of the houses were of the worst, was in large measure due to flies acting as carriers of the specific bacilli, which, in fact, were isolated from a number of flies caught in two undrained privies, on the fences and house walls, and in the room of a typhoid patient. In 1910, Bertarelli, in an investigation of 100 flies caught in a household of the better class