HOUSE FLIES AS CARRIERS OF BACTERIA 339 



were found to be infected with the bacillus. It was also found that the 

 wings, heads, legs and bodies of the flies, when removed with sterile 

 forceps and placed in sterile broth, gave positive results ; several other 

 experiments were carried out along the same lines, and the authors 

 concluded that Musca domestica can convey the typhoid bacillus from an 

 infected stool to sterile petri dishes, and such contamination may take 

 place under natural conditions. 



In 1903 Ficker conducted some similar experiments in Leipzig, and 

 found that typhoid bacilli could be recovered from Musca domestica 

 twenty-three days after they had been ingested. Graham- Smith examin- 

 ed a large number of specimens of Musca domestica, C. erythrocephala 

 and C. vomitoria for intestinal bacteria of the colon type, and found 

 that the highest degree of infection was present in those flies which 

 were caught near decaying animal matter, and the next highest in those 

 caught near manure. Surface infection was two and a half times more 

 frequent than intestinal infection. In two instances an organism giving 

 the cultural reactions of Bacillus dysenteriae, Flexner, was isolated. Later 

 this observer recorded some more experiments, as a result of which he 

 concludes that, though non-sporing bacteria only survive a few hours on 

 the legs and wings of flies, yet they may infect sterile agar plates for 

 several days. This is due, according to Graham- Smith, to the fact that 

 the fly, when it feeds, regurgitates some of the contents of its crop, in 

 which the bacteria may survive for several days ; the same holds good 

 for the contents of the intestine, though he considers that there is no 

 evidence to show that bacteria multiply in the intestine of the fly. These 

 experiments were carried out with a number of bacteria, among which 

 where Bacillus typhosus, B. enteritidis, B. tuberculosis, B. diphtheriae 

 and the cholera vibrio. The typhoid bacillus was recovered as late as 

 the sixth day, and the tubercle bacillus as late as the third. The diph- 

 theria bacillus was short lived, and the cholera vibrio was recovered on 

 the third day from the intestines of the flies. 



In some later experiments Graham-Smith finds that the typhoid bacil- 

 lus may remain alive in the intestines of Musca domestica for at least 

 six days after acquiring the infection. The tubercle bacillus will live in 

 the fly for ten days and the spores of Bacillus authracis can be recovered 

 twenty days after they have been ingested. 



Cox, Lewis and Glynn recently carried out a series of experiments on 

 the number and varieties of bacteria carried by Musca domestica in sani- 

 tary and insanitary areas ; they arrived at the following results : 



1. More than 450 flies were found naturally infected, and 123 strains 



