FATE OF ORGANISMS EATEN BY LARVA 121 



renKjved and placed in the lioxes described. The flies infected the food in the cage 

 to some extent. 



" The larvte developed rapidly in each box and the pupce when formed were 

 transferred to fresh boxes containing clean sterile sand. The flies began to emerge 

 in about a month. 



"Cultures from the control flies showed no organisms similar to those which had 

 been used for infecting purposes. At first cultures were made from single flies, but 

 as these yielded negative results, batches of lo flies were later emulsified and the 

 emulsion plated on MacConkey plates. No colonies of B. prodigioszis developed on 

 any of the plates although cultures were made from a large number of flies. In 

 searching for B. typhosus, B. enteritidis, and Morgan's bacillus, MacConkey's 

 medium was used. Numbers of colonies of non-lactose fermenting bacilli developed 

 and from each plate several colonies were picked off and put through various tests in 

 order to establish their identity. Neither B. typhosus nor B. enteriluiis was ever 

 isolated. Eight colonies of Morgan's bacillus were, however, obtained, three from 

 flies which emerged from larvte fed on sterilized freces, four from flies which emerged 

 from larvii2 fed on unsterilized faeces, and one from flies which emerged from larva; 

 fed on sterile food." 



" The foods used seemed to exercise little effect. These 

 experiments again indicate that Morgan's bacillus and certain 

 other non-lactose fermenters can survive the metamorphosis. On 

 the other hand, it cannot be claimed that they conclusively prove 

 that other organisms, such as B. typhosus and B. enteritidis, are 

 entirely incapable of surviving, since all the colonies were not 

 tested and some undetected examples of these organisms may 

 have been present on the plates. Nevertheless sufficient colonies 

 were isolated and tested to show that these organisms very rarely 

 survive sufficiently long to appear in adult flies under the experi- 

 mental conditions. Under natural conditions it is certain that 

 if such organisms happen to be present in the material in which 

 the larvje feed they have to compete with many varieties of 

 organisms better adapted to the conditions prevailing in the 

 intestine of the larvae, and their persistence in large numbers 

 is improbable." 



The varieties of non-lactose fermenting bacilli found in flies 

 from difl'erent sources are fully discussed in Chapter xiv. 



From his experiments the writer came to the following 

 conclusions : 



( i) "The blow-flies which develop from larvae allowed to 

 feed on the bodies of animals dead of infection due to B. enteri- 

 tidis or B. anthracis are not infected with these organisms. 



(2) " A large proportion of the house-flies {M. doniesticd) 



