STAPHYLOCOCCUS AND BACILLUS PRODIGIOSUS 291 



on the carcases of pigs which had died from swine fever during 

 an epidemic in 1905. Each fly was allowed to walk over an agar 

 culture plate for about one minute. From one of the plates the 

 bacillus of swine fever was isolated. The flies were swarming on 

 the carcases of the dead animals and were frequently seen to pass 

 directly from each source of infection to the feeding troughs of 

 the pigs. 



Staphylococci were found by Joly (1898) on a house-fly caught 

 in the laboratory. Celli {I.e.) also records experiments which 

 indicated that 8. pyogenes aureus retains its virulence after passing 

 through the intestine of the fly. 



Reference has been previously made to experiments with 

 Bacillus procligiosus which was used on account of its suitability 

 in the case of experiments with flies, being non-pathogenic, non- 

 spore-bearing and easily recognisable. There are a number of 

 records of other experiments on the carriage of the bacillus by flies. 



Abel (1899, cited by Nuttall and Jepson) refers to an experi- 

 ment of Otto Helm in 1875 who stated that the slimy masses 

 containing the bacillus " Monas prodigiosus" are easily conveyed 

 from one food substance to another. Abel placed cultures of B. pro- 

 digiosus and clean potatoes in different parts of a room. To the 

 potatoes he added putrid meat so that the odour would attract 

 the flies. After 2 — 3 days colonies of B. prodigiosus appeared in 

 all the potatoes. Negative results were obtained when the room 

 was rid of flies. Similar experiments by Burgess are mentioned 

 by Hart and Smith (1898). Flies were fed on material containing 

 B. prodigiosus and then allowed to fly in a large room. After 

 a few hours the flies were recaptured and allowed to walk over 

 slices of sterilised potato on which colonies of the bacillus subse- 

 quently developed. Abel records two instances in which he 

 observed spontaneous infection of food by flies in houses where 

 they were abundant. Flies were captured in these houses and 

 placed singly in tubes containing sterilised potato. Seven of 

 twenty-eight flies so captured in one house gave B. prodigiosus 

 and a similar positive result Avas given by three out of thirty-three 

 flies caught in the other house. Abel accordingly points out the 

 possibility of flies carrying the bacilli of typhoid and cholera in a 

 similar manner. 



19—2 



