404 



SCIENCE. 



[N. S. Vol. XXIII. No. 585, 



must elapse before the contaminated mos- 

 quito is capable of infecting, points to a 

 definite cycle of development in that insect ; 

 (3) the limitation of its developmental 

 cycle to mosquitoes of a single genus, and 

 to a single vertebrate, conforms to a natural 

 zoological law and does not agree with our 

 present knowledge of the life history of 

 bacteria; (4) the effects of climate and tem- 

 perature upon Stegomyia, and upon the 

 rate of development of the yellow-fever 

 parasite within the body of that insect, are 

 exactly the same as the effects of the same 

 conditions upon the Anopheles mosquito 

 and the malarial parasite. 



Consequently, although on account of its 

 minute size no one has ever been able to 

 identify the organism of yellow fever either 

 in human blood or tissues, or in the mos- 

 quito, we feel justified in regarding it as 

 an obligate animal parasite. If this be 

 correct it can not maintain its vitality in 

 water, in soil nor in any other material, no 

 matter how badly they may chance to have 

 been contaminated. Experience and ex- 

 periments have shown that such is actually 

 the case; that dead bodies can be freely 

 handled and dissected by non-immunes 

 without danger; that non-immune persons 

 may live in intimate contact with the gar- 

 ments, bedding and clothing used and 

 soiled by yellow-fever patients, under the 

 same conditions and in the same climate 

 where yellow fever has prevailed, and suffer 

 no inconvenience. And further, it has 

 been shown by the French commission that 

 this organism fails to survive in blood, a 

 most excellent culture medium, after it 

 has been kept for forty-eight hours under 

 ordinary conditions. This undoubtedly 

 proves the inability of the organism to 

 maintain its vitality in filth or decomposing 

 organic matter. 



Yellow fever is non-contagious, for in our 

 medical literature niunerous instances are 



recorded where numbers of patients were 

 brought to certain places for treatment and 

 no secondary cases resulted. This was be- 

 fore the days of disinfection, before any 

 precautions were taken against mosqui- 

 toes, and at a time when intercourse with 

 the sick was free and unrestricted. These 

 strange occurrences were observed in Spain 

 during a severe epidemic at Barcelona in 

 1821, during which, under the supposition 

 that the air of the city was infected, there 

 was a general exodus to the country. Here 

 hundreds came down with the disease and 

 were treated, but not a single case was re- 

 corded to have appeared in a person who 

 had not visited the city. Yet tons of 

 furniture and baggage were carried from 

 infected houses into the country. All this 

 took place in a warm climate and during 

 the ravages of a devastating epidemic. 

 Such remarkable occurrences were inex- 

 plicable mysteries that puzzled the most 

 brilliant medical minds of the day; they 

 could only be explained upon the theory 

 that the air of the city had become con- 

 taminated. And so it had, but not with 

 poisonous gases and noxious vapors as they 

 supposed, but with infected mosquitoes. 

 In the light of the mosquito theory the ex- 

 planation is clear. An epidemic prevailed 

 in Havana during the early part of that 

 season, and a number of cases appeared on 

 vessels after leaving there for the Spanish 

 port, where the epidemic appeared later in 

 the season. The first eases in Barcelona 

 were seen on the vessels f i*om Havana, lying 

 in the harbor; then persons living in the 

 city, but who had visited or were em- 

 ployed on the vessels, were taken sick; and 

 later, the epidemic raged throughout vari- 

 ous parts of the city. It is quite evident 

 that the vessels carried infected mosquitoes 

 as well as others that were not infected; 

 these mosquitoes bred rapidly in the houses 

 on shore and the conditions then became 



