34 Poisonous Arthropods 



species and insects transmitting disease, we shall discuss here only 

 the poison of the mosquitoes. 



It is well known that mosquitoes, when they bite, inject into the 

 wound a minute quantity of poison. The effect of this varies accord- 

 ing to the species of mosquito and also depends very much on the 

 susceptibility of the individual. Soon after the bite a sensation of 

 itching is noticed and often a wheal, or eminence, is produced on the 

 skin, which may increase to a considerable swelling. The scratching 

 which is induced may cause a secondary infection and thus lead to 

 serious results. Some people seem to acquire an immunity against 

 the poison. 



The purpose of this irritating fluid may be, as Reaumur suggested, 

 to prevent the coagulation of the blood and thus not only to cause 

 it to flow freely when the insect bites but to prevent its rapid coagula- 

 tion in the stomach. Obviously, it is not developed as a protective 

 fluid, and its presence subjects the group to the additional handicap 

 of the vengeance of man. 



As to the origin of the poison, there has been little question, 

 until recent years, that it was a secretion from the salivary glands. 

 .,...., , , , . Macloskie (1888) showed 



/-j^ /TipAt d!ftrticulum of suction sta/inafi ^ ' 



'1^;;,2X^,:;<.^ ' ' that each gland is sub- 



i, .-DoriaL ileod reel *-> 



divided into three lobes, 



the middle of which differs 



from the others in having 



„, „. ,,.,., . , evenly grantilated contents 



24. Diagram of a longitudinal section of a mosquito. 



and staining more deeply 

 than the others (fig. 24). This middle lobe he regarded as the source 

 of the poison. Brack, (1911), by the use of water, glycerine, chloro- 

 form, and other fluids, extracted from the bodies of a large number 

 of mosquitoes a toxine which he calls cuUcin. This he assumes 

 comes from the salivary glands. Animal experimentation showed 

 that this extract possessed hemolirtic powers. Inoculated into the 

 experimenter's own skin it produced lesions which behaved exactly 

 as do those of mosquito bites. 



Similarly, most writers on the subject have concurred with the 

 view that the salivary glands are the source of the poison. How- 

 ever, recent work, especially that of Nuttall and Shipley (1903), 

 and Schaudinn (1904), has shown that the evidence is by no means 

 conclusive. Nuttall dissected out six sets (thirty-six acini) of glands 

 from freshly killed Culex pipiens and placed them in a drop of salt 



