52 The Book of Hu^s. 



In old times vessels lying" two miles from shore, absolutely 

 cut off from communication, have vet been scourged with 

 the plague, and men wondered why. Now they know. 

 In November, 1901, there were no cases or deaths from 

 that disease in the Cuban capital, the like of which had 

 not been for a hundred and thirty years. November had 

 always been the worst month of all. In November, 189(5, 

 there were 244 deaths from yellow fever in Havana. 

 Systematic extermination of mosquitoes was introduced 

 there in February, 1901, and that it was worth while to 

 pour kerosene on puddles of water is proved by the fact 

 that from April i to December 5 of that year there \vere 

 only five deaths from yellow fever, and no cases at all 

 during the last three months of that year. Mosquitoes 

 are still to be found, but only about one-tenth as fre- 

 quently as before. 



Yellow fever is a germ-disease. The tiny organism 

 which causes the trouble lives in the red corpuscles of 

 the blood. It throws off little spores, as does this white 

 Empusa that kills the flies on the window-panes. These 

 spores float around and seize upon and destroy other red 

 corpuscles until the patient dies. Supposing him not to 

 have been bitten by a mosquito, that ends the career of 

 that set of germs, for their full life-round is not complete 

 until they have been taken, with the blood of a human 

 being, into the stomach of a mosquito of the Anopheles 

 kind. Not otherwise can there be any mating of the 

 germs. Certain of them, which undergo no development 

 in the human body, when they find themselves in the 

 stomach of the mosquito, go on to maturity, unite, and 

 send forth elementary forms which work their way 

 through the stomach of the mosquito into the salivary 

 glands, and are jetted with that droplet of poison into 

 the veins of the next human being she bites. The 



