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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 401 



against the spread of the infection by flies, or the same would 

 apply to the typhoid bacillus, whose carriage by flies is 

 proven. Axenfeld mentions L. Miiller and Lakah and Khouri 

 as advocating the view that flies may spread the infection 

 more readily. In view of the fact that, as the same author 

 states, " Koch- Weeks conjunctivitis is to be classed with the 

 most contagious infectious disease which we know of," it is 

 important that the role of flies should be fully recognised. 

 Notwithstanding the occurrence in this country of flies in less 

 numbers than in such countries as Egypt, it would be well to 

 bear in mind the probable influence of flies in cases of acute 

 conjunctivitis, such as those described by Stephenson (1897) 

 in our own country. The sole difference between the disease 

 in Egypt and here is, as Dr. Bishop Harman points out to me 

 in a letter, that " the symptoms produced (in Egypt) are, from 

 climate and dirtiness of the subjects, more severe, and that 

 there is found a greater number of cases of gonorrhceal 

 disease than in England"; and, I would add, a far greater 

 number of flies. This disease is eminently suited for dissemi- 

 nation by flies, both on account of the accessibility of the 

 infectious matter in the form of a purulent discharge from 

 the eyes and on account of the flies' habit of frequenting 

 the eyes. 



6. Plague. 



Although fleas are considered to be the chief agents in the 

 dissemination of the plague bacillus in spite of the fact that 

 the proof is not absolutely convincing, it is nevertheless 

 interesting, and certainly not unimportant, to refer to the 

 series of experiments of Nuttall (1897) on M. domestica. 

 In these experiments he conclusively proved that flies were 

 able to carry the plague bacillus, and that they subsequently, 

 died of the disease. Flies were fed upon the crushed organs 

 of animals which had died of plague. Control flies were fed 

 in a similar manner on the organs of uninfected animals, and 

 the control experiments were kept under the same conditions. 



