318 MOSQUITOES OF NORTH AMERICA 
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, however, the mosquito be killed as soon as the poison is introduced, 
the latter will have to be absorbed by the human system and the disintegrated 
blood mass with it. This is the basis of fact behind the popular belief that a bite 
does not hurt if you allow a mosquito to complete its meal and withdraw the 
lancets naturally.” 
The popular belief referred to by Smith in this last sentence seems to have a 
basis of exact observation, and such an observation was originally made by Hum- 
boldt in the early part of the last century. Humboldt states that when one lets 
a mosquito suck its fill there is no swelling and no pain. He often tried the ex- 
periment on himself, in the valley of the Rio de la Magdalena, on the advice of 
the natives. He wondered whether the insect only injects the poison at the 
moment when it is frightened away, or whether it sucks back the poison when 
it is allowed to suck as much as it will. He inclined to the latter opinion, for 
when he allowed Culex cyanopterus * to peaceably bite the back of his hand, he 
noticed that the pain, which was very strong in the beginning, diminished as the 
insect continued to pump up the blood and that it ceased absolutely at the 
moment when the sucking was finished. One of the writers is inclined to be- 
lieve from his own experience that when a mosquito is allowed to drink her fill 
there is less irritation than when she is frightened away by an ill-advised slap. 
RELATIVE SUSCEPTIBILITY. 
The amount of irritation caused by the poison of mosquitoes varies greatly 
with different individuals. This was already pointed out by Humboldt and 
other early writers. Some people suffer severely from their bites, while others 
are not at all affected. This is a matter of common observation. We have 
already shown in quoting from Réaumur severe instances of the irritation caused 
by the bites of many of these insects, which caused the limbs to swell until 
amputation was seriously considered. Réaumur also brings out the point of 
relative susceptibility. He found that not only are peasants with sun-burned 
and work-hardened skin bitten as often as ladies with delicate skin, but he states 
that he has observed that among ladies with whom he happened to be in the 
country, some were attacked while others with equally fine skin were not at- 
tacked. Arguing then that certain skins are distasteful to mosquitoes he con- 
sidered that there must be some means of rendering all skins distasteful. He 
advocates experimenting with different liquids for this purpose and especially 
decoctions of such plants as the mosquitoes seem to avoid, as he had noticed 
them to leave some plants immediately after alighting on them. Smith’s obser- 
vations on this point are interesting : 
“ Susceptibility to mosquito poisoning varies enormously. Some persons do 
not even notice ea ey biting under ordinary conditions, though they may be 
honestly unaware of their exemption. I remember enjoying a drive with a man 
* Probably the species described by Humboldt as Oulew cyanopennis (Voyage aux Reg. 
equinoct. ae p. 340 (1819) ) : we have not been able to identify it. wee . 
