For everybody knew just how to fight that most panic-striking plague, yellow fever; everybody had a different idea of just how to combat it. You should fumigate silks and satins and possessions of folks before they _left_ yellow fever towns--no! that is not enough: you should burn them. You should bury, burn, and utterly destroy these silks and satins and possessions before they _come into_ yellow fever towns. It was wise not to shake hands with friends whose families were dying of yellow fever; it was perfectly safe to shake hands with them. It was best to burn down houses where yellow fever had lurked--no! it was enough to smoke them out with sulphur. But there was one thing nearly everybody in North, Central, and South America had been agreed upon for nearly two hundred years, and that was this: when folks of a town began to turn yellow and hiccup and vomit black, by scores, by hundreds, every day--the only thing to do was to get up and get out of that town. Because the yellow murderer had a way of crawling through walls and slithering along the ground and popping around corners--it could even pass through fires!--it could die and rise from the dead, that yellow murderer; and after everybody (including the very best physicians) had fought it by doing as many contrary things as they could think of as frantically as they could do them--the yellow jack kept on killing, until suddenly it got fed up with killing. In North America that always came with the frosts in the fall.... This was the state of scientific knowledge about yellow fever up to the year 1900. But from between his mutton chop whiskers Carlos Finlay of Habana howled in a scornful wilderness: “You are all wrong--yellow fever is caused by a mosquito!” II There was a bad state of affairs in San Cristobal de Habana in Cuba in 1900. The yellow jack had killed thousands more American soldiers than the bullets of the Spaniards had killed. And it wasn’t like most diseases, which considerately pounce upon poor dirty people--it had killed more than one-third of the officers of General Leonard Wood’s staff, and staff officers--as all soldiers know--are the cleanest of all officers and the best protected. General Wood had thundered orders; Habana had been scrubbed; happy dirty Cubans had been made into unhappy clean Cubans--“No stone had been left unturned”--in vain! There was more yellow fever in Habana than there had been in twenty years!