250 THE CARRIAGE OF TYPHOID FEVER BY FLIES 



may not necessarily indicate recent contamination with human 

 excrement. 



Aldridge (1907) isolated a bacillus, apparently belonging to the 

 paratyphoid group, from flies caught in a barrack latrine in India 

 during an outbreak of enteric fever. In appearance and behaviour 

 to tests it Avas very similar to B. typhosus. 



A series of careful experiments were made by Sellars^ in con- 

 nection with Niven's investigations on the relation of flies to 

 infantile diarrhoea. Out of thirty-one batches of house-flies care- 

 fully collected in sterilised traps in several thickly populated 

 districts in Manchester he found, as a result of cultural and inocu- 

 latory experiments, that bacteria having microscopical and cultural 

 characters resembling those of the Bacillus coli group were present 

 in four instances, but they did not belong to the same kind or 

 variety. 



In a report of investigations carried out at the Central Research 

 Institute of India by Thomson (1912), the following conclusions 

 are given : " The ingestion of typhoid germs in large numbers has 

 no bad effect on the health of the flies; they can retain living 

 typhoid bacilli within their bodies and transmit infection thereby 

 for a period of twenty-four hours after ingestion ; the}' can carry 

 the living germs on the exterior of their feet or bodies for a period 

 of six hours, and so transmit infection." 



Graham-Smith (1910) carried on infection experiments with 

 B. typhosus. Flies were fed on syrup infected with this bacillus 

 and afterwards on plain syrup. Sixteen hours after the removal 

 of the infected syrup cultures on Drigalski-Conradi medium were 

 made of the intestinal contents of five flies ; eight flies were 

 allowed to walk on culture plates and plates were also sown with 

 emulsified faeces. B. typhosus was recovered in all cases. This 

 experiment was repeated with flies, two days, three days, and daily 

 to six days after infection. The results showed that B. typhosus 

 may remain alive in the intestinal canal for at least six days and 

 that flies may infect plates upon which they walk for at least 

 forty-eight hours after infection. 



A typical instance of a small epidemic of typhoid fever is 



1 Recorded in the Report on the Health of the City of Manchester, 1906, by 

 James Niven, pp. 86 — 96. 



