Arthropods as Simple Carriers of Disease 



that from feeding on excrement, on sputum, on open sores, or on 

 putrifying matter, the flies may pass to the food or milk upon the table 

 or to healthy mucous membranes, or uncontaminated wounds. 

 There is nothing in its appearance to tell whether the fly that comes 

 blithely to sup with you is merely unclean, or whether it has just 

 finished feeding upon dejecta teeming with typhoid bacilli. 



109. Pulvillus of foot of house-fly, showing glandular hairs. 



The method of feeding of the house-fly has an important bearing 

 on the question of its ability to transmit pathogenic organisms. 

 Graham-Smith (1910) has shown that when feeding, flies frequently 

 moisten soluble substances with "vomit" which is regurgitated from 

 the crop. This is, of course, loaded with bacteria from previous 

 food. When not sucked up again these drops of liquid dry, and pro- 

 duce round marks with an opaque center and rim and an intervening 

 less opaque area. Fly-specks, then, consist of both vomit spots 

 and feces. Graham-Smith shows a photograph of a cupboard window 

 where, on an area six inches square, there were counted eleven hundred 

 and two vomit marks and nine fecal deposits. 



