BACTERIA ON FLIES UNDER NATURAL CONDITIONS 297 



bacteria carried inside the fly is very much greater tliaii 

 those carried externally. 



2. Flies caught in insanitary or congested areas of the 

 city carried and contained fai- more bacteria (aerobic), 

 including those of the intestinal group, than flies from tho 

 more sanitary, that is, cleaner, less congested or su])urban 

 districts. The number of aerobic bacteria obtained from 

 flies caught in insanitary districts varied from 800,000 to 

 500,000,000 per fly ; flies from the cleaner or less congested 

 areas gave from 21,000 to 100,000 bacteria per fly. 



3. Flies caught in the dwelling rooms of different 

 corporation houses forming two sides of a street about 

 400 yards long which constituted a sanitary " oasis " in the 

 middle of a slum district carried and contained less bacteria 

 of all kinds than those from the dwelling rooms of a street 

 with insanitary property on each side. 



4. The number of intestinal bacteria as indicated by 

 glucose bile salt fermenters is greater in insanitary or con- 

 gested areas, where they vary in number from 10,000 to 

 3^33,000,000 than in the more sanitary areas where from 

 100 to 10,000 are carried per fly. 



5. Pathogenic bacteria and those allied to the food- 

 poisoning group were only obtained from the congested or 

 moderately congested areas and never from the suburban 

 districts. 



6. Flies caught in milk shops apparently carry and 

 contain more bacteria than those from shops with exposed 

 food in a similar neighbourhood. The authors attribute 

 this fact to the milk being a suitable culture medium for 

 bacteria after having been inoculated by the flies, later they 

 re-inoculate themselves. 



7. A comparison of the number of bacteria carried by 

 flies and blue-bottles caught in an eating-house opposite to 

 slaughter-houses showed that the latter carried a much 

 greater number. 



