30 LICE AND THEIR MENACE TO MAN 



no poisoning effect, or the nature of the wound 

 made may obviate the necessity for its injection. 

 Insects such as mosquitoes and fleas*, if they do 

 not draw blood at once from the place they choose, 

 move quickly and try in another spot ; but the 

 louse very rarely does this, generally waiting 

 patiently for the blood to collect. It is essential 

 that such an insect should cause little pain during 

 the actual process of feeding, so as not to attract 

 the attention of its host to its ultimate cost. 



The blood when recently taken in shows very 

 distinctly red in the gut, but soon takes on a 

 black colour owing to the action of the digestive 

 juices. As the feeding louse approaches repletion 

 it usually begins to defaecate. It is a wasteful 

 feeder, and sometimes blood almost unchanged 

 can be seen passing out of the anus while it is 

 still gorging itself. The excreta has been shown 

 to be of very great importance in relation to the 

 disease-conveying capacity of the insect. The 

 amount passed is considerable, a well-fed adult 

 louse excreting as much as seventy to eighty-five 

 granules a day. It is sometimes ejected in rough 

 masses and sometimes in a long spirally coiling 

 thread, or again in a fluid condition which quickly 

 dries up. In bulk, for in experimental work it 

 can be collected in surprisingly large quantities, 

 it has the appearance and colour of finely ground 

 coffee. Under the microscope it is seen to con- 

 sist of rough black granules and smooth red 

 pieces. It is very easily blown about and can be 



