CONTAMINATION THROUGH INTERNAL INFECTION 228 



alive 1)11 the legs and wings for at least 18 hcjurs after feeding. In 

 exceptional cases it may remain alive longer. In the contents of 

 the crop and intestine and on the proboscis it is present for four or 

 five days, after which tinie its ninnbers gradually diminish and 

 after 17 days the cultures yielded negative results. 



A careful series of experiments with a view to determining 

 whether H. prodigiosus multiplied in the crop appeared to indicate 

 that no multiplication takes place. In this connection it may be 

 remarked that NicoU (1911), to whose experiments reference will 

 be matle later, finds that certain of the non-lactose fermenting 

 bacteria appear to be capable of multiplying in the intestine of 

 the fly. 



The extent to which the persistence of B. prodigiosus, and no 

 doubt other bacteria of like character, in the faecal deposits, that 

 is, the infectivity of the flies in this respect, is affected by the 

 character of the food, is shown by a series of experiments in which 

 the faeces from infected flies which had been fed on milk, s^Tup 

 and sputum were collected at various periods and cultures made. 

 B. prodigiosus was not recovered after 48 hours from the faeces of 

 flies fed on sputum. The faeces of flies fed on milk contained the 

 bacteria, that is, were infective, for seven days and those of flies fed 

 on syrup for four days after feeding. 



That infected flies will infect both liquid and solid food upon 

 wdiich they feed was show^n by feeding flies artificially infected 

 with B. prodigiosus and also B. pyocyaneus on milk and with the 

 former organism on sugar. It was shown that flies infected with 

 these non-spore-producing organisms were able, by feeding upon 

 it, to contaminate milk for ten or eleven days (in the case of 

 B. prodigiosus). That the contamination would appear to have 

 been solely from the alimentary tract <jr proboscis was shown by 

 the fact that the organism (B. prodigiosus) could not be cultivated 

 from the limbs of the infected flies eleven davs after infection, 

 although the limbs were heavily contaminated on the second day. 

 After feeding flies on s}Tup infected with B. prodigiosus it was 

 shown that they could infect sugar, by being allowed to feed upon 

 it subsequently, for at least two days. 



Flies, when unusually liungTv, will suck at the deposits of 

 other flies which they may find, in the same way that they will 



