332 READINGS IN BIOLOGICAL SCIENCE 



and at this time there were probably not less than 6,000 persons ill with 

 the fever." Dr. Rush, then a physician in Philadelphia, relates that a cheer- 

 ful countenance was scarcely to be seen in the city for six weeks. Once in 

 entering the house of a poor man, he met a child of 2 years who smiled in 

 his face, and he says, "I was strangely affected by this sight. Few persons 

 were met in the streets except those who were in quest of a physician, a 

 nurse, or the men who buried the dead. The hearse alone kept up the re- 

 membrance of the noise of carriages or carts in the street." 



For more than 200 years, learned men searched for the clues that would 

 tell them how to prevent the crime of yellow fever which was repeated 

 year after year. The strange part of the story is that they found the clues 

 and described them many times, but they didn't have sufficient knowledge 

 to trace the villain. It lived in the community undisturbed and went its 

 criminal way unchecked, until the master detective, using the very same 

 clues that puzzled everyone else, came along and pointed it out. 



The first thing Major Reed and his associates decided to do when they 

 reached Cuba was to sift the evidence that seemed to point to an insect- 

 carrier of the disease. Insects, like flies and mosquitoes, had already been 

 convicted of carrying certain other diseases. Walter Reed himself had 

 proved that flies spread typhoid fever; and an English army surgeon. Dr. 

 Ross, had discovered that the parasite of malaria gets into the blood of a 

 human being through the bite of an A?wpheles mosquito and in no other 

 way. Another species of mosquito had been suspected of carrying yellow 

 fever. There were many clues that pointed to it as the guilty party. 



THE FIRST CLUE 



In almost all the old accounts of yellow fever epidemics, mosquitoes 

 were mentioned as being very troublesome. Dr. O'Halloran, describing an 

 outbreak of the disease in Barcelona, Spain, in 182 1, wrote: "It is worthy 

 of remark that during the month (July) the flies and mosquitoes were in- 

 finitely multiplied." Dr. Drysdale, a Baltimore physician, writing of an 

 epidemic, said: "Locusts were not more numerous in the reign of Pharaoh 

 than mosquitoes through the last few months; yet these insects were very 

 rare only a few years past, when a far greater portion of Baltimore was a 

 marsh." Thus it appears that the suspect was at the scene of the crime. 



THE SECOND CLUE 



Epidemics always started in the low wet regions or near the docks. All 

 epidemics in Baltimore broke out at Locust Point, a low-lying section al- 

 most surrounded by water, or about the docks and wharves. 



The report of the epidemic in Mobile, Ala., in 18 19 says the first cases 

 were among the people employed on the wharves. "A number of car- 

 penters and sailors employed about the wharf and who were much on board 

 the schooner Sally which was filled with stagnant water, and about the 



