LIFE-HISTORY OF THE BODY-LOUSE 29 



To return to the feeding louse : there is a 

 pause while the salivary juice acts on the blood 

 and then sucking commences. In one in which 

 the chitin is fairly transparent the pumping 

 pharynx can be seen expanding and contracting 

 with a rapid movement which is almost a flicker, 

 and the blood can be seen collecting in the gut. 

 At the same time waves of contraction are seen 

 to pass along the alimentary canal. The louse 

 is a slow feeder and may occupy half an hour or 

 more in completing its meal, and it is rarely that 

 it finishes in under fifteen minutes. This slow 

 feeding is unusual in blood-sucking insects, but 

 is more than paralleled by the African tick 

 (Orniihodorus moubata), which has the nocturnal 

 habits of the bed-bug, and often occupies two or 

 three hours over its meal. 



Of blood-sucking insects those which cause 

 most pain by the actual operation of biting are 

 the flies belonging to the genus Tabanidae : the 

 horse-flies, chegs, blind-flies, etc. These insects 

 alight on the skin and with their powerful jaws 

 make gashed wounds from which blood flows. 

 This they imbibe quickly, and the wounds often 

 continue to bleed after they have left. It is not 

 often that such an insect obtains a full meal from 

 a man at the first attempt, as he strikes at once 

 at the position of the bite if his hands are un- 

 occupied. In these cases, however, there is 

 usually no subsequent irritation from the bite, 

 so that the salivary juice, if such is injected, has 



