41 



apparently complete recovery of the patient. By the agency of flies 

 which visit such excrement the bacilli may be carried far and wide to 

 food supplies, and by their consumption may enter the digestive tract 

 of many healthy individuals. 



An investigation has been carried on in this office for the purpose 

 of ascertaining just what flies breed in human excrement or are in 

 the habit of visiting such substances, and, conversely, just what flies 

 are found in dining rooms and kitchens where food is being served 

 and prepared. These investigations have been conducted with the 

 utmost care and in many different parts of the country. A very 

 large amount of material was studied, and the detailed results were 

 published in the proceedings of the Washington Academy of Sciences 

 (Vol. II, pp. 451-604). Briefly summarized, it was found that the 

 number of species of insects which breed in or frequent human excre- 

 ment is very large. There are many beetles (44 species, and many 

 hymenopterous parasites); none of these, however, are especially 

 significant in this connection. Flies are the important creatures, and 



Fig. 20. — Musca domestica: Puparium at left; adult next, with enlarged antenna; larva and enlarged 

 parts at right— enlarged (original). 



of these 77 species were studied. Thirty-six of them were found to 

 breed in human faeces, while 41 were simply captured while visiting 

 this substance or feeding upon it. Some, of course, were scarce and 

 others were very abundant. 



Now, in order to ascertain exactty which ones of these are important 

 in the disease-bearing function more than 2,300 flies were caught in 

 kitchens and dining rooms in different parts of the country from Mas- 

 sachusetts to California and from New York to Louisiana, and were 

 all carefully examined. It was proven that of the excrement flies six 

 species are found in houses in sufficient numbers to constitute them 

 dangerous species. The most abundant species found in or on excre- 

 ment do not occur in kitchens and dining rooms, but, as just stated, 

 these six species are sufficiently abundant in both relations to become 

 very dangerous. 



At the head of these six species must stand the common house fly, 

 Musca domestica (fig. 20). This insect constituted over 98 per cent of 



