28 AGRICULTURAL EXPERIMENT STATION. 



should be any pain from the introduction of the minute lancets- 

 of the insects, and the small amount of blood-letting is usually a 

 benefit rather than otherwise. Unfortunately, however, in its 

 normal condition the human blood is too much inclined to clot to 

 be taken unchanged into the mosquito stomach ; hence, when the 

 insect bites, a minute droplet of poison is introduced, whose 

 function it is to thin out the fluid and make it more suitable for 

 mosquito digestion. It is this poison that sets up the inflam- 

 mation and produces the irritation or swelling. If Ave make a 

 puncture wound with a fine needle, a small droplet of blood will 

 exude which will almost at once harden into a clot, and if we 

 attempt a little later to break that clot, we will find it tough and 

 hard to disintegrate. If we allow a mosquito to bite until it is 

 fully gorged and then smash it, we find that the blood from the 

 gorged abdomen is much more fluid and spreads out thin. If 

 we further allow it to dry, there will be no clot ; but a thin spread 

 of material which is brittle and breaks readily into little frag- 

 ments. 



Figure 6. 



Section of head of Culex, showing location of poison gland at P. 

 from Howard "Mosquitoes," by permission.) 



(After Macloskie, 



The pain is caused entirely by the action of the poison in' 

 breaking up the blood, and as the first act of a biting mosquito 

 is to introduce this poison into the wound, the pain and inflam- 

 mation will be the same, whether the insect gets its meal or not. 

 In fact, it has been said that if a mosquito be allowed to suck its 

 fill and then fly, the bite will not itch, and there is just a basis 

 of justification for this. The poison introduced will act upon 

 just so much blood, and if that be absorbed with the poison by 

 the insect, little or nothing will be left in the wound. If, how- 

 ever, the mosquito be killed as soon as the poison is introduced^ 



