204 ZOOLOGY 



scope, and can be traced without difficulty in both 

 its hosts. Long ago people connected malaria with 

 swamps, the word itself, from the Italian, meaning 

 "bad air," which was supposed to rise at night from the 

 stagnant waters. We now know that Anopheles breeds 

 in the swamps, and flies at night; it is the swarm of 

 mosquitoes, which arise and bite whoever may be acces- 

 sible, that bring about the disease. The malaria organ- 

 ism has a double life-cycle, reproducing sexually in the 

 body of the mosquito and asexually in the blood of man. 

 Thus we must regard the mosquito as the primary host, 

 or the more important of the two from the standpoint of 

 the parasite. At the time of reproduction or sporula- 

 tion in the blood, the affected individual suffers a "chill," 

 followed by fever, which occurs at regular intervals while 

 the active phase of the disease lasts. There are several 

 types of malaria, and at least three different species of 

 parasites have been distinguished, all, however, car- 

 ried by Anopheles. The proof of the connection be- 

 tween mosquitoes and malaria was established not only 

 by the observation of the organisms in the blood, but 

 also by the experimental transmission of the disease. It 

 was also shown experimentally that men could live and 

 work in the most malarious districts, and suffer no harm, 

 provided they were protected from mosquitoes at night. 

 In localities where there is no Anopheles, malaria cannot 

 be acquired, though persons who have acquired it else- 

 where may continue to suffer at intervals. Anopheles 

 may even be present, but unless it is infected by the 

 Plasmodium, no malaria results. 



Sleeping 7. The important African diseases due to trypano- 



andnagana somes are also carried by insects, but of a different 



family of Diptera or flies. In this case the alternate 



hosts are species of tsetse fly, of the genus Glossina. 



