106 SANITARY ENTOMOLOGY 



every instance. Step by step, he proved that fly-larva take up bacteria 

 from their food, and when breeding in flesh may take up disease germs as 

 well as non-pathogenic germs; that these germs may pass tmaltered 

 through the insects' intestines and out in their feces; that some of them 

 may remain for a long period in the intestinal canal, and some even 

 may multiply therein; that they may be taken up by the larva and per- 

 sist through its metamorphosis until it arrives at the adult stage, and 

 for days thereafter, and may be carried by this adult and deposited 

 with its feces on food or excrement ; and that these bacteria will also be 

 fov/nd in the glutinous substances surrounding the eggs when deposited, 

 and thus contaminate the substance in which the newly born larvae will 

 feed; and of course be taken up by this second generation and possibly 

 be distributed farther by it. 



These facts were worked out by Cao in 1905 and 1906, and yet 

 Graham-Smith credits Faichnie (who worked in India in 1909) with be- 

 ing the first one to suggest that bacteria ingested by the larva might 

 survive the pupal stage and be present in the intestine of the adult. 

 Later, JBacot, and also Ledingham in 1911 and Graham-Smith in 1912, 

 corroborated these claims that the bacteria could persist in the body 

 throughout the metamorphosis. 



Ledingham (1911), Nicholls (1912), and Graham-Smith (1912) 

 have shown that the fly larvae have great powers of destroying micro- 

 organisms due to the fact that many of these organisms are not adapted 

 to the conditions prevailing in the interior of the larva and pupa, or 

 perhaps more correctly due to the hostile action of bacteria which more 

 normally frequent the intestines of the larva. These normal inhabitants 

 of the fly intestine are principally non-lactose fermenting organisms. 



Not only bacteria but also protozoa, such as the amoebae of dysen- 

 tery, and the eggs of parasitic worms, may be taken up by the fly larvae or 

 adults and deposited in the feces. Roubaud (1918) has brought out 

 the fact that multitudes of the amoebic dysentery germs taken up by 

 adult flies and deposited in their feces die because of the rapid drying 

 of the feces, and he credits the fly with being a great agent in the de- 

 struction of multitudes of protozoa, while granting the equally great 

 opportunity of the fly to contaminate food therewith. 



Stiles in 1889 fed larvae of Musca domestica with female Ascarii 

 lumbricoides, which they devoured, together with the eggs they con- 

 tained. The larvae as well as the adult flies contained the eggs of 

 Ascaris (Nuttall, 1899, p. 39). NicoU (1911) has very thoroughly in-' 

 vestigated the relationships of flies to the possible carriage of eggs of 

 worms and demonstrated the ability of adult flies to ingest the eggs of 

 various species of worm^, provided these are small enough, and to pass 



