670 DISEASES CAUSED BY FILTRABLE VIRUS 



microscopic. Blood serum, filtered or unfiltered, becomes non-infectious 

 when heated to 56 C. for ten minutes. 



Mode of Transmission. Until comparatively recent years the mode 

 of transmission of yellow fever was not understood and many erroneous 

 theories were prevalent. It was supposed that yellow fever was conta- 

 gious, and transmitted from person to person by direct or indirect con- 

 tact with those afflicted or by fomites. The first to make the definite 

 assertion that yellow fever was transmitted by the agency of mosquitoes 

 was Carlos Finlay. Finlay, 1 as early as 1881, advanced the theory that 

 mosquitoes were responsible for the transmission of this disease and, fur- 

 thermore, recognized " Stegomyia fasciata " or " Stegomyia calopus " as 

 the guilty species. Finlay 's opinion, although later proved to be.correct, 

 was at first based only upon such circumstantial evidence as the corre- 

 spondence of the yellow-fever zones with the distribution of this species 

 of mosquito and the great prevalence of mosquitoes at times during 

 which epidemics occurred. His theory was, therefore, received with 

 much skepticism and was neglected by scientists until its revival in 

 1900, when the problem was extensively investigated by a commission 

 of American army surgeons. 



Reed, Carroll, Agramonte, and Lazear were the members of this 

 commission. The courage, self-sacrifice, and scientific accuracy which 

 characterized the work of these men have made the chapter of yellow 

 fever one of the most brilliant in the annals of American scientific 

 achievement. 



Their work was much facilitated by the experience of Gorgas 2 and 

 others, who had demonstrated the absolute failure of ordinary sanitary 

 regulations to limit the spread of yellow fever. 



They began their researches by investigating carefully the validity 

 of Sanarelli's claims as to the etiological significance of his "Bacillus 

 icteroides." The results of this work yielded absolutely no basis for 

 confirmation. 



They then proceeded to investigate the possibility of an intermediate 

 host. 



In August, 1900, the commission began its work on this subject by 

 allowing mosquitoes, 3 chiefly those of the stegomyia species, to suck 



1 Finlay, Ann. Roy. Acad. d. Havana, 1881. 



2 Gorgas, Jour, of Trop. Med., 1903. 



8 Reed, Carroll, Agramonte, and Lazear, Phila. Med. Jour., Oct., 1900; also Am. 

 Pub. Health Assn. Rep., 1903; Agramonte, N. Y. Med. News, 1900; Reed, Jour, of 

 Hyg.. 1902; Reed, Carroll, and Agramonte, Am. Medicine, July, 1901. Boston Med. 



