2o6 INSECTS 



some way these gather into the saUvary glands, and 

 when that mosquito bites again, it introduces with its 

 droplet of saliva a large number of "sporozoits" which, 

 if they find conditions favorable, enter red blood- 

 corpuscles and set up a case of malaria. 



The transmission of this disease, then, is by no means 

 a simple matter, and the proper species of Anopheles is 

 absolutely essential to it. The elimination of these mos- 

 quitoes from any locality would carry with it the elimi- 

 nation of malarial troubles as well. It may be inter- 

 esting to note in this connection that the species of 

 Anopheles live easily in settled communities, enter 

 houses freel}' where they can manage it, and that the 

 female passes the winter in the adult stage in cellars, 

 coming up occasionally into well-warmed rooms and 

 even biting. Normally, they do not become active 

 until well along in May or in June, when eggs are 

 laid by the female which has been fertilized the 

 previous fall. 



All stages of the parasites causing the various forms 

 of malaria have been followed in both man and the 

 mosquito, and no part of the history above given is 

 guess-work. The connection between the Stegomyia 

 mosquito and yellow-fever is equally certain, though the 

 specific parasite has never been made out in either man 

 or insect. Direct experiment has furnished convincing 

 proof of the connection, and the treatment of yellow- 

 fever epidemics has entered a new phase. The efficient 

 work done in the Panama Canal Zone has demonstrated 

 that the disease is quite controllable through the insect 

 and, incidentally, collections made by entomologists 

 from the U. S. Department of Agriculture at Washing- 

 ton, have shown that this Stegomyia is never found 

 away from human settlements. The relation, then, is 

 extremely close between this insect and man, and they 



