HOUSE FLIES AS CARRIERS OF BACTERIA 341 



bacteria rapidly disappeared from the larvae, whenever they were removed 

 from the infected material, and none of the bacteria could be found 

 in the pupae. From these experiments and several others carried out 

 along the same lines, Nicholls concludes that a recently hatched fly 

 may be considered to be sterile, and that it is not likely that flies bred in 

 infected material will be themselves infected. 



In a still more recent paper Tebbutt records a long series of experi- 

 ments which he carried out in order to confirm the work of Ledingham 

 and others. He came to the following conclusions : 



1. Pathogenic organisms such as B. dysenteriae (Type ' Y ') cannot 

 be recovered from pupae or imagines reared from larvae to which these 

 organisms have been administered. 



2. When the larvae have been bred from disinfected ova, and are 

 subsequently fed on B. dysenteriae (Type ' Y ')> this organism may be 

 successfully recovered from the pupae and imagines in a small proportion 

 of cases. 



3. Under similar conditions B. typhosus was not recovered in a 

 single case from pupae or imagines. 



4. In those cases in which B. dysenteriae (Type ' Y ') was successfully 

 recovered from pupae, the colonies on the plate were invariably fewer than 

 those obtained from pupae and imagines after administration to the 

 larvae of more adaptable organisms such as ' Bac. A ' (.Ledingham). 



5. When organisms such as ' Bac. A ' were administered to larvae 

 bred from disinfected ova, or non-disinfected ova contaminated with this 

 organism, it was in many cases possible to recover the organism from 

 pupae and imagines. 



6. In none of the pupae examined, after administration to the larvae 

 of either B. dysenteriae or ' Bac. A ', was it possible to recover the 

 organism in every instance. A certain proportion of pupae in both cases 

 proved sterile, so that the process of metamorphosis is undoubtedly 

 accompanied by a considerable destruction of the bacteria present in the 

 larval stage. 



7. The temperature at which the larvae develop (19 to 25 C.) has 

 probably an important bearing on the survival of the pathogenic organ- 

 isms such as Bac. ' V ' of dysentery, administered in association with 

 organisms such as Bac. 'A ', in view of the fact that the latter grows 

 far more luxuriantly at this temperature. Even when grown in broth at 

 37 C. (the optimum temperature for Bac. ' Y ') together with Bac. ' A ', 

 the Bac. ' Y ' was found to form after two days only one-quarter of the 

 total number of bacteria present in the mixed growth. 



