2 26 POPULAR SCIENCE MONTHLY. 



pointment. Eepeated examinations of blood from patients in every 

 stage of the disease failed to demonstrate the presence of micro- 

 organisms of any kind. My subsequent investigations in Havana, Vera 

 Cruz and Eio de Janeiro, made in 1887, 1888 and 1889, were equally 

 unsuccessful. And numerous competent microscopists of various na- 

 tions have since searched in vain for this elusive germ. Another method 

 of attacking this problem consists in introducing blood from yellow 

 fever patients or recent cadavers into various ^culture media' for the 

 purpose of cultivating any germ that might be present. Extended re- 

 searches of this kind also gave a negative result, which in my final re- 

 port I stated as follows : 



The specific cause of yellow fever has not yet been demonstrated. 



It is demonstrated that micro-organisms, capable of development in the cul- 

 ture-media usually employed by bacteriologists, are only found in the blood and 

 tissues of yellow fever cadavers in exceptional cases, when cultures are made 

 very soon after death. 



Since this report was made various investigators have attacked the 

 question of yellow fever etiology, and one of them has made very posi- 

 tive claims to the discovery of the specific germ, I refer to the Italian 

 bacteriologist, Sanarelli. His researches were made in Brazil, and, 

 singularly enough, he found in the blood of the first case examined by 

 him a bacillus. It was present in large numbers, but this case proved to 

 be unique, for neither Sanarelli nor any one else has since found it in 

 such abundance. It has been found in small numbers in the blood and 

 tissues of yellow fever cadavers in a certain number of the cases ex- 

 amined. But carefully conducted researches by competent bacteriolo- 

 gists have failed to demonstrate its presence in a considerable propor- 

 tion of the cases, and the recent researches of Eeed, Carroll and Agra- 

 monte, to which I shall shortly refer, demonstrate conclusively that the 

 bacillus of Sanarelli has nothing to do with the etiology of yellow fever. 



So far as I am aware. Dr. Carlos Finlay, of Havana, Cuba, was the 

 first to suggest the transmission of yellow fever by mosquitoes. In a 

 communication made to the Academy of Sciences of Havana, in Oc- 

 tober, 1881, he gave an account of his first attempts to demonstrate the 

 truth of his theory. In a paper contributed to the 'Edinburgh Medical 

 Journal' in 1894 Dr. Finlay gives a summary of his experimental inocu- 

 lations up to that date as follows : 



A summary account of the experiments performed by myself (and some 

 also by my friend. Dr. Delgado), during tlie last twelve years, will enable the 

 reader to judge for himself. The experiment has consisted in first applying a 

 captive mosquito to a yellow fever patient, allowing it to introduce its lance and 

 to fill itself with blood; next, after the lapse of two or more days, applying the 

 same mosquito to the skin of a person who is considered susceptible to yellow 

 fever; and, finally, observing the effects, not only during the first few weeks, but 

 during periods of several years, so as to appreciate the amount of immunity 

 that should follow. 



