﻿MICKO-ORGANISMS BY FLIES IN SAINT LUCIA. 



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Therefore, for practical considerations, as regards the conveyance of organisms 

 causing disease, a freshly hatched fly may be considered as probably sterile,* and 

 there is not much likelihood of its acquiring these organisms by contact with the 

 material in which it bred. 



Fig. 2. — Sarcophaga auriflnis, Walk. X 6. 



Observations on the transmission of micro-organisms by adult flies. 



The period of the infectivity is very different during the imaginal stage of 

 the fly. 



If the common house fly {Musca domesticd) is placed in a cage and its food 

 infected with an organism, this organism can easily be isolated from the fly for 

 24 hours afterwards, but it will be found that this period of starvation has greatly 

 reduced the number of organisms in its intestinal tract. 



I have elsewhere described an experiment with the " ulcer fly " (Oscinis pallipes, 

 Lw.), in which the fly was fed upon pus from a boil caused by Staphylococcus 

 pyogenes var. aureus, and this organism was cultured from the fly 24 hours after 

 it had fed. I believe that the majority of cases of yaws (framboesia) in the 

 West Indies are caused by the inoculation of surface injuries by this fly. They 

 feed only on the skin discharges of man and other animals, and though rare in 

 the town of Castries, they are very numerous in the country districts of St. 

 Lucia, and can be seen hovering round the bare legs and arms of labourers, 

 searching for abrasions or the secretions of the sweat and sebaceous glands. The 

 persistence of these little flies is extraordinary ; they must be brushed off by 



* [Mr. A. Bacot has recently proved (c/. Proc. Ent. Soc. Lond. 1911, p. 497) that in the case 

 of Musca domestica, if the larva be infected with Bacillus pyocyaneus, the infection may be 

 carried right through to the newly emerged imago, positive results having been obtained by 

 him in every instance. In view of this, it seems probable that Dr. Nicholls has under-estimated 

 the significance of the fact that in his experiment with Sargophaga a similar transmission took 

 place in 2 cases out of 12. — Ed.] 



