GNATS, MIDGES, AND MOSQUITOES 243 



therefore, from that point of view, a poison could not be 

 an advantage. If, therefore, a poison exists, its func- 

 tion must undoubtedly be, to facilitate the drawing of 

 the blood, and not to serve as a weapon. 



Influenced by the anatomical difficulties above men- 

 tioned, other observers have maintained that no poisonous 

 fluid is injected, but that the laceration of tissues pro- 

 duced by the six minute, acutely pointed, and in some 

 cases barbed, organs which constitute the borer, is 

 sufficient to account for the inflammation and itching. 

 This hypothesis, again, is not without objection. It 

 would appear that the insect sometimes experiences diffi- 

 culty in getting at the blood it desires, for deep per- 

 forations of the skin may be made without drawing 

 blood, and then no swelling occurs, and little pain is 

 felt : this certainly appears a formidable difficulty in the 

 way of the latter explanation. Mr. G. Dimmock, one of 

 the most recent experimenters with Culices, forcibly says : 

 " I am convinced that there is use made of a poisonous 

 saliva, for when biting, if the mosquito fails to draw 

 blood, which it often does on parts of the back of my 

 hand, it may have inserted its proboscis nearly full 

 length in from one to six directions in the same place, 

 and withdrawn it again ; indeed, it may have inserted its 

 proboscis, as often occurs, in extremely sensitive parts ; 

 yet in such cases, if no blood be drawn, no more effect 

 is produced upon my skin than is produced by the prick 

 of a sharp needle; a red point appears, only to dis- 

 appear in a few hours. Certainly there has been as 

 much tearing of tissues in such a' case as above men- 

 tioned as there is when the gnat settles on a place 

 richer in blood, and with a single probing draws its 

 fill." He remarks also that "the poisonous effect on 

 me, as proved by numerous experiments, is in direct 



