()60 TRANSMISSION OF YELLOW FEVER BY MOSQUITOES. 



also the fact that the opidomic extension of the disease depends upon 

 external eonditions relating to temperature, altitude, rainfall, etc. 

 It was a well-established fact that the disease is arrested by cold 

 weather and does not prevail in noilhern latitudes or at considerable 

 elevations. But diseases which are directly transmitted from man to 

 man b}^ personal contact have no such limitations. The alternate 

 theory took account of the above-mentioned facts and assumed that 

 the disease was indirecth* transmitted from the sick to the well, as is 

 the case in typhoid fever and cholera, and that the germ was capable 

 of development external to the human body when conditions were 

 favorable. These conditions were believed to be a certain elevation 

 of temperature, the presence of moisture, and suitable organic })al)u- 

 lum (tilth). The two first-mentioned conditions were known to be 

 essential; the third was a subject of controversy. 



Yellow-fever ei)idemics do not occur in the winter months in the 

 temperate zone, and th«\v do not occur in arid regions. As epi- 

 demics have frecjuently pi'evailed in seacoast cities known to ))<^ in an 

 insanitary condition, it has been generally assumed that the presence 

 of decomposing organic material is favorable for the development of 

 ;in epidemic, and that, like typhoid fev(U' and chol(>ra. yellow fever is 

 a "tilth disease." Opposed to this view. how(>ver, Avas the fact that 

 epidemics have frequently occuiied in localities (e. g., at military 

 posts) where no local insanitai'v conditions were to be found. More- 

 over, there are marked ditierences in regard to the transmission of the 

 recognized filth diseases — typhoid fever and cholera — and yellow fever. 

 The first-mentioned diseases are largely propagated by means of a 

 contaminated-water supply, whereas there is no evidence that yellow 

 fever is ever conmnmicated in this way. 



Typhoid fever and cholera prevail in all parts of the world and may 

 prevail at any season of the year, although cholera as a rule is a disease 

 of the summer months. On the other hand, yellow fever has a very 

 restricted area of prevalence, and is essentially a disease of seaboard 

 cities and of warm climates. Evidentl}' neither of the theories referred 

 to accounts for all of the observed facts with reference to the endemic 

 prevalence and epidemic extension of the disease under consideration. 



Having for years given nmch thought to this subject, I became 

 some time since impressed with the view that probablj^ in yellow fever, 

 as in the malarial fevers, there is an intermediate host. I therefore 

 suggested to Doctor Keed, president of a board ^ appointed upon my 

 recommendation for the study of this disease in the island of Culia, 

 that he should give special attention to the possibilit}^ of transmission 

 by some insect, although the experiments of Finlay seemed to show 



*The members of the board were: Maj. Walter Reed, surgeon, U. S. A.; Dr. James 

 Carroll, contract surgeon, U. S. A.; Dr. A. Agramonte, contract surgeon, U. 8. A., 

 and Dr. Jesse Lazear, contract surgeon, U. S. A. 



