FLIES AND DISEASE 177 



surface it will set up woolsorter's disease. It, to- 

 gether with the flea, is accused of transmitting the 

 plague bacillus, not only from man to man, but from 

 rat to man. Flies are active agents in disseminating 

 cholera ; and anyone who has watched them cluster- 

 ing around the inflamed eyes of the children in Egypt, 

 or in Florida, will not readily acquit them of being the 

 active agents in the spread of inflammatory ophthalmia 

 or of ' sore eye.' 



It is worthy of note that after exhaustive experi- 

 ments on the tsetse fly (Glossina palpalis\ which 

 conveys that most fatal of diseases, sleeping-sickness, 

 Professor Minchin and his colleagues, Mr. Gray and 

 Mr. Tulloch, have come to the conclusion that the 

 Protozoon (Trypanosoma gambiense) which causes the 

 disease does not as might be expected pass through 

 certain stages of its life -history in the fly, but is 

 mechanically conveyed upon the biting mouth parts 

 of the insect. The deadly parasite is, indeed, so easily 

 cleaned off these appendages that a single bite is 

 sufficient to wipe them off. A tsetse fly which has 

 bitten an infected person will set up the disease in the 

 next person (or monkey) it bites; but the insertion of 

 the proboscis, quick and instantaneous as it is, serves 

 to clean it to wipe off adhering trypanosomes, and if 

 it now bite a second person (or monkey), it fails to con- 

 vey the disease. This is a most important discovery, 

 and contrary to what we should have expected; but 

 our knowledge of the history of the genus Trypano- 

 soma is still too small to justify generalization, difficult 

 as it is to .avoid it. The diseases which in our country 

 are disseminated by flies are all bacterial and all 

 mechanically conveyed. 



In passing, it is worth recording that, contrary to 

 the usual statement that tsetse flies are confined to the 

 continent of Africa, Captain R. M. Carter* has recently 



* Brit. Med.Journ., No. 2,394, November 17, 1906, p. 1393. 



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