INSECTS AS INTERMEDIATE HOSTS 



409 



the growth of the larva and the pupa. 

 Without such breeding places, one 

 year would see the end of all mos- 

 quitoes in all civilized communities. 

 In larger bodies of water, where fish 

 may be kept, these will usually de- 

 stroy the larvae and thus prevent 

 the multiplication of mosquitoes ; 

 but in the shallow margins, where 

 the fishes cannot reach them, the 

 mosquitoes have things their own 

 way. Here it is necessary to keep 

 the borders of the ponds clear of 

 weeds, sedges, etc. 



The practical effect of extermi- 

 nating the mosquito is shown by the 

 decrease of malaria (or yellow fever). 

 Fig. 212 shows the results for the 

 island of Cuba. A similar record 

 stands to the credit of our national 

 government in connection with the 

 work of digging the Panama Canal. 

 The region through which the canal 

 runs was a veritable plague spot. 

 During the various attempts of the 

 French engineers to construct the 

 canal, disease made the completion 

 of the work practically impossible. 

 When the United States took over 

 the enterprise, the first step was 

 the establishment of sanitary con- 

 ditions ; and the largest part of 

 the problem was the extermination of the mosquito through 

 draining and filling in, and the inspection of inhabited regions 

 to prevent the maintenance of breeding places for the insects. 



1870 1880 1890 1895 1897 1899 1901 

 1896 1898 1900 



FIG. 212. The reduction of 

 yellow fever in Cuba 



The mortality from this disease had 

 always been very high, but much 

 worse in some years than in others. 

 The year 1896 was unusually bad, 

 and 1897 not much better. Imme- 

 diately after the American army of 

 occupation began to clean up in 

 Havana, in 1898, the sanitary condi- 

 tions showed marked improvement. 

 By eliminating the breeding places 

 of mosquitoes, yellow fever has been 

 completely banished from the island 



