342 MEDICAL ENTOMOLOGY 



8. There was no evidence that the larval juices contained substances 

 bacteriacidal for Bac. ' Y '. The bacillus died more rapidly in normal 

 saline solution. 



9. The possibility of flies becoming infected from the presence of the 

 pathogenic organisms in the breeding grounds of the larvae may be 

 considered to be remote. 



The above represents the results of experiments carried out in 

 temperate climates, where Musca domestica seldom has opportunities of 

 breeding in human excrement. In the tropics, on the other hand, it and its 

 allies are always found breeding in night soil trenches, and are therefore 

 much more likely to ingest pathogenic bacteria in their larval stages ; 

 here again the number of associated bacteria is very much greater and 

 the chances of the pathogenic bacteria surviving in the pupae and 

 imagines are smaller. It should be noted, however, that in the 

 tropics, where typhoid and cholera carriers are numerous, and where 

 the various stages of the house fly are rapidly passed through, this 

 may be a common method of infection. Whether this is so or not, 

 the fact remains that house flies, if they feed on infected material, 

 such as human excrement, containing the cholera vibrio, the bacilli 

 of dysentery and typhoid, or the various bacilli associated with 

 infantile diarrhoea, are capable not only of carrying the germs of 

 these diseases on their legs and proboscidies but also in their 

 intestinal tracts, and when voiding their faeces on food they may 

 infect it. 



In order to study the relation which Musca domestica or any of its 

 allies may have to the transmission of pathogenic bacteria, it is necessary 



B..I- A* to be able to breed the flies in large numbers, and to 



Breeding technique 



keep them in captivity under as near as possible 

 natural conditions. A simple technique, not requiring elaborate and 

 costly apparatus, must be used so that it can be controlled with the 

 least amount of supervision. It is also very important for the worker 

 to know for certainty that he is dealing with the same species of Musca 

 throughout his experiments. 



If the worker is desirous of breeding Musca nebulo and what applies 

 to this species holds good for all the others a number of flies should 

 be caught in a small net around food in the bazaar shops or from a 

 night soil trench, and at once transferred to large test tubes. In 

 catching flies indiscriminately in this way it will be obvious that there 

 may be more than one species of Musca in the tubes. It is, therefore, 

 very necessary for the worker to decide as to how many species there are 



