[hewitt] FEEDING HABITS OF THE STABLE FLY 41 



deposits are passed during the second 26-hour period, during which 

 time, apparently, the meal is most actively digested. 



The fact that the meal is chiefly digested during the first forty- 

 eight hours, as indicated by the rate of defaecation, is supported by 

 the volume of the faeces. Taking the diameter of the faecal spots 

 as a measure of their comparative volume, it was found that during 

 the first twenty-four hours after feeding the brown faecal deposits 

 which are first passed when digestion begins had an average diameter 

 of 1 mm. The subsequent dark-brown deposits passed during the 

 same 24-hour period measured on the average -77 to 1 mm. in diam- 

 eter. The average diameter of the dark brown faecal deposits 

 passed during the second 24-hour period after feeding was -7mm., 

 and the blackish-brown deposits of the third 24-hour period were 

 uniformly -5mm. in diameter. 



Examination of faecal deposits. 



A large compound faecal depoist, such as the flies frequently 

 made when resting after a meal and defaecating in the same place, 

 which has been passed between five and seventeen hours after feeding 

 on human blood, was examined. It was dark, blackish-brown in 

 colour and viscous in texture. After being crushed in 20 per cent, 

 glycerine it was examined under the oil-immersion (1 -9 mm. obj., No. 

 15 oc). The dissolved faecal deposit was reddish to brown in colour, 

 and full of reddish granular particles of dissolved blood. Haemo- 

 globin crystals and remains of white blood corpuscles indicated that 

 although most of the blood is digested, some of it passes over un- 

 digested and the presence of haemoglobin in the faeces is important 

 as indicating the possibility of the survival of micro-organisms in 

 faeces not subjected to desiccation after ejection. 



A freshly deposited dark brown faecal spot, deposited 23 à hours 

 after feeding (human blood) was removed by my friend, Mr. H. T. 

 Giissow, with sterilized water, and examined for bacterial organisms. 

 Not a single organism could be found, but easily recognisable remains 

 of blood which remained unstained by the carbol fuchsin were notice- 

 able. Except for a light meal on beef gelatin stained with nigrosin, 

 which almost proved fatal, this fly had only fed on my blood since 

 its emergence from the pupa; nevertheless, the absence of bacteria 

 from the faeces is somewhat surprising. 



Frequency of feeding. 



As a rule Stomoxys will not feed a second time within twenty-four 

 hours of feeding, if the meal was a complete one. In one case a fly 



