no CITY FLIES 



CHAPTER X 



THE BACTERIOLOGY OF CITY FLIES 



Two important contributions to the general bacteriology of 

 city flies have been published recently, one by Torrey (191 2) 

 working in New York and the other by Cox, Lewis and Glynn 

 (191 2) working in Liverpool. 



Torrey (191 2) investigated in detail the bacterial content of 

 a considerable number of flies caught entering the windows of 

 the Loomis Laboratory, Cornell University Medical School, 

 New York. The flies caught were amongst those continually 

 circulating in and out of the open windows of a row of tenements 

 of the poorer grade 75 ft. distant. The flies caught in large 

 sterile test-tubes were examined in lots of ten. 



"They were shaken for 5 minutes in lo c.c. of sterile normal salt solution, and the 

 wash was set aside and labelled I. The flies were then rinsed thoroughly in 10 c.c. of 

 salt solution, which was drained off and discarded. The washed flies were next 

 placed in lo c.c. of the salt solution and the abdomens were so squeezed with a sterile 

 platinum spatula that the contents of the intestine exuded into the fluid. The 

 thoroughly emulsified intestinal matter of lo flies was labelled II. Platings were 

 made from I and II, suitably diluted, in agar, litmus lactose agar and Conradi-Drigalski 

 medium. These plates were incubated 24 hours at 37° C. The number of colonies 

 on the nutrient agar plates was taken as the total count.. ..The types of colonies, which 

 appeared to be dominant, were isolated and identified, and in addition a special search 

 was always made for colonies of the dysentery bacillus type." 



He found that up to the latter part of June the flies were 

 free from fscal bacteria, showing mainly cocci. " During July and 

 August there occurred periods in which the flies examined carried 

 several millions of bacteria, alternating with periods in which the 

 number of bacteria was reduced to hundreds." He thinks "the 

 scanty flora probably indicated the advent of swarms of recently 

 hatched flies." " The bacteria in the intestines of the flies were 

 8"6 times as numerous as on the surface of the insects." Bacilli 

 belonging to the colon group were three times as numerous in 

 the intestine as on the surface. The figures given in his table 

 show 'that the surface contann'nation of these 'wild' flies may 



