INSECT " PORTERS " OF DISEASE 2I/ 



cesspit and pupate. The contents of the puparium are as 

 a rule sterile, and in the freshly hatched flies, though 

 some spores and spore-bearing organisms are to be found, 

 both the ordinary intestinal organisms and the colour- 

 producing ones, added for experimental purposes, are 

 absent. 



The danger of these flies crawling on the faecal mass 

 and conveying portions of it on to animal food are of 

 course great. Fortunately fresh meat is a greater 

 attraction to them than cold cooked food, and the flies 

 do not frequent houses to the same extent as the 

 M. domestica. 



Almost all the intestinal organisms belonging to the 

 bacteria can be conveyed by flies in one way or other, 

 and some experiments (Graham Smith) show that it is 

 possible that eggs of tapeworms may be conveyed in this 

 manner to susceptible animals, and so the infective agents 

 may be distributed. M. domestica is the chief offender, 

 and Bahr has shown that the prevalence of the dysentery 

 season in Suva, Fiji, is related to the prevalence of this 

 fly. Experimentally it can be shown that all the intestinal 

 organisms, pathogenic as well as non-pathogenic, can be 

 conveyed by the fouled flies and foul articles of food, 

 milk, sugar, cooked meat, &c. They undoubtedly spread 

 ophthalmia, as \vhen fouled by the discharges from the 

 conjunctiva they can, if they settle on or near the eyes 

 of other persons, by regurgitation, direct fouling or defaeca- 

 tion, deposit the germs in the vicinity of the eyes, when 

 they will be readily introduced. 



Yaws is sometimes spread similarly, as the flies can 

 convey Spirochceta pertenuis from the yaws tubercle to any 

 ulcerated or abraded surface on which it rests. 



Some flies, as Glossina, are nearly pupiparous. They 

 deposit larvae which are so mature that they are ready to 

 pupate, and when passed do not feed, but are still motile 

 and can pass into loose earth and there pupate. These 

 flies may act as direct " porters " of trypanosomes, as 

 when disturbed in feeding on an animal in whose blood 



