220 THE DISSEMINATION OF PATHOGENIC ORGANISMS BY FLIES 



desiccation for a short time. The last factor is the presence of 

 suitable culture media, such as certain foods, or moist surfaces as 

 the mouth, eyes, or wounds, f(jr the reception of the (n-ganisms 

 which have been carried in the digestive tract or on the body or 

 appendages of the fly. If these conditions are satisfied the possi- 

 bility of M. domestica or its allies playing a part in the trans- 

 ference of the infection should be carefully considered, and this 

 suggestive or circumstantial evidence will be discussed in certain 

 of the diseases which folhjw, in addition to the epidemiological 

 and bacteriological evidence. 



Historical. 



There is no doubt that if a careful search were made in old 

 writings many references would be found attributing unhealthy 

 conditions to the presence of flies. The idea is a very old one, 

 the scientific examination and experimental proof, however, is of 

 comparatively recent date. 



Mercurialis in 1577 (quoted by Nuttall), believed that flies 

 carried the virus of plague from persons suffering from the disease 

 to the food of healthy people. Riley (191t)) refers to an early 

 and remarkable statement of Kircher who, in his Scrutiniunt 

 Physico-medicum, published in Rome in 1658, said: "There can 

 be no doubt that flies feed on the internal secretions of the 

 diseased and dying, then flying away, they deposit their excretions 

 on the food in neighbouring dwellings, and persons who eat it are 

 thus infected." Kircher attributes this theory to Mercurialis. 

 Sydenham (1666) considered that if swarms of house-flies were 

 abundant during the summer, the autumn would be unhealthy, 

 although Holscher (1848) disagreed with this idea. Ci-awford 

 (1808) believed that insects in a general way, especially house-flies, 

 acted as disseminators of disease. Leidy (1871) declared his belief 

 that house-flies were responsible for the spread of hospital gangrene 

 and wound infection during the American Civil War and re- 

 affirmed his convictions in later writings. In 1871 Lord Avebury 

 called attention to the habits of flies which alight on decomposing 

 substances and carry impurities especially the secretions of un- 

 healthy wounds. Rather than regard them as dipterous angels 



