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NOTES ON THE SPECIES OF THE (tENUS MUSCA, LINNAEUS— PART 1. 



By Major W. S. Pattox, M.B., ETLS., I. M.S. (retired), 



Lecturer on I:n/oinoloi:\' und I'arasifoloi^y, lu/iiihiirgli l'}iiveysity. 



Of the many insects which we now kiiow to be dangerous menaces to the health 

 of man, the house-fly, Musca domestica, has few (if any) equals, but the facts relating 

 to its germ-transmitting capacity are unfortunately still verj^ incomplete. In the 

 case of those Anopheline mosquitos which transmit the parasites of malaria, and 

 the tsetse-flies, which infect man and other animals with trypanosomes, we are in a 

 position to estimate the inefliciency and loss of life directly attributable to them, for 

 in each case we know most of the species directly responsible for the dissemination 

 of these parasites. But in the case of the house-fly we have no conclusive proof 

 that Bacillus typhosus, for instance, is carried by one, or more than one, species of 

 Musca. Further, by the time the cases are diagnosed, the infected flies have either 

 died or disappeared, and it is rarely possible to trace the infection to them. It is 

 true, however, that many observers have recorded the finding of pathogenic bacteria 

 in, and on, species of Musca, but the final proof of the identity of these bacteria has 

 invariably been faulty. Yet in spite of these discrepancies there is no doubt, from 

 everyday practical observation the world over, that one, and more than one, species 

 of Musca regularly carry the bacilli of the enteric fever, cholera and dysentery groups, 

 as well as niany other pathogenic organisms, especially the virus of trachoma, from 

 infected material and deposit them on food and the human body. In investigating 

 outbreaks of infectious diseases the house-flv shoifld alwa3's be considered as a possible 

 vector of the causal organisms. 



The fact that the Culicidae contain among their members many serious pests 

 has led to an intensive study of the species of the world, resulting in numerous 

 valuable monographs and papers describing the species, and every medical man is 

 now able to determine with certainty almost any species for himself. So also in the 

 case of the tsetse-flies we have Austen's complete handbook available for the deter- 

 mination of the species ; and similarly with many other insect pests. This systematic 

 work on these important insects is very necessary, for it facilitates further 

 biological studies, and, more particularly, accurate information on their relation 

 to disease-causing germs. 



But when we come to consider the all-important house-fi}', Musca domestica 

 and its allies, we find that although there are many valuable papers and books dealing 

 with this species from the disease standpoint, there is no systematic work of any value 

 which would enable the sanitary offlcer in the tropics to determine with accuracy 

 the species which may call for enquiry during the course of his work. He cannot 

 help but call all the species of Musca by the specific name domestica, for he believes 

 that a house-fly with a striped thorax is Musca domestica all the world over. And 

 there is every reason that he should do so, for in such an authoritative work as that 

 on " The House Fly, Musca domestica, L." by the late Dr. Gordon Hewitt, w^e have 

 a definite statement that the house-fly found throughout the world, and especially 

 in tropical countries, is Musca domestica, L., and this statement has been accepted 

 and copied by all subsequent writers on the subject. I propose to question it. That 

 both tire sexes of one of the species of Musca found in the tropics are very similar to 

 Musca domestica is quite true, but when we come to compare the male with the male 

 (5296) 2 H 



