I04 DISTRIBUTION OF BACTERIA 



{h) Experiments designed to ascertain wJiether flics can infect 

 flnids on zvhich they feed. 



In 1909 the writer carried out some experiments on this 

 subject but they were few in number and inconchisive, so in 1910 

 he (Graham-Smith, 1911) re-investigated the subject using both 

 M. doniestica and C. erytJirocepJiala, the latter having been bred 

 in captivity from eggs. The fluids used for the experiments 

 were syrup and steriHzed milk. Two out of several experiments 

 are quoted. 



Experiments ivitJi house-flies {M. domestical. 



Six flies were carefully fed on an emulsion of B. prodigios?is 

 which was placed on the floor of their cage in single drops. 

 During the process of feeding the flies did not fall into the syrup 

 or soil their wings. Their proboscides and legs were the only 

 organs which could become infected by direct contact with 

 contaminated syrup. They were then transferred to a clean 

 cage. Sterile milk was poured into a sterile watch-glass and 

 the latter was placed in the incubator until some of the milk 

 had evaporated and a rim of partially dried milk was left round 

 the fluid portion. Three hours after the flies had fed on the 

 infected emulsion, a watch-glass of sterile milk was placed in 

 the cage, and left there for some hours. It was noticed that the 

 flies fed on the dried parts as well as on the fluid milk. On 

 examination of the watch-glass after it had been removed from 

 the cage, there was noticed on the areas covered with partially 

 dried milk, not only numerous proboscis marks, but also several 

 red marks produced by vomit composed of an emulsion of 

 B. prodigiosus. Cultures were made from {a) the fluid milk, 

 {b) the dried parts (not obviously contaminated with vomit) and 

 {c) vomit marks. Similar experiments were carried out 24, 26 

 and 28 hours after the infection of the flies with positive results 

 as shown in Table 14. 



