124 FATE OF ORGANISMS EATEN BV LARVA 



under conditions which would exclude the possibilit}' of re- 

 infection. 



Before forming a final judgment his experiments ought to be 

 repeated with suitable precautions against re-infection. 



It must be remembered, however, that under natural conditions 

 flies which emerge from infected larvae may be able to re-infect 

 themselves if the contaminating organism still survives in the 

 material surrounding the pupse. 



One point, however, has been clearly demonstrated. Both 

 the larva and adult fly have a peculiar flora, consisting, so far 

 as is at present known, of non-lactose fermenting organisms, 

 adapted to life within their alimentary canals, and capable of 

 surviving the pupal stage. These bacilli are of considerable 

 practical importance since they are often present in large 

 numbers and render the search for pathogenic bacilli of the 

 typhoid-enteritidis group one of great labour, since they resemble 

 them in many cultural characters and can only be certainly 

 distinguished from them by means of elaborate cultural and 

 serological tests. 



CHAPTER XII 



FLIES AND 'SPECIP^IC DISEASES 



Though there is at the present time a widespread tendency 

 to believe that under special conditions non-biting flies are 

 often partly responsible for the spread of certain diseases, few 

 undoubted instances of infection by flies have yet been recorded. 

 This is partly due to the fact that sufficient attention has not 

 been devoted to the enquiries ; partly to the difficult}' of 

 excluding other possible sources of infection and partly to the 

 difficulty of obtaining direct proof of infection by flies alone. 



In dealing with each specific disease the evidence relating to 

 the possibility of the virus being distributed by flies will be 

 summarized under the following headings : 



