XI] MODE OF INFECTION 185 



others were allowed to go out of it. After these preliminary 

 precautions, some Stegomyia that had fed 12 days previously 

 on a yellow fever patient in the first stages of the disease, were 

 allowed to bite twelve persons. Ten of them became infected 

 after incubation periods varying from 41 hours to five days. 

 Twelve other persons who remained in the camp never shewed 

 the slightest signs of infection, although living in close proximity 

 with these yellow fever patients. 



This experiment proved that not only is this mosquito the 

 carrier of the infection, but that contact with patients is 

 harmless. The latter is most important from an economic 

 point of view, and therefore the commission carefully inves- 

 tigated the question. 



A mosquito-proof house was constructed so as to present 

 the worst possible hygienic conditions. It was badly venti- 

 lated, and badly lighted, and the windows were kept shut all 

 day. The air inside the house was very humid and the tem- 

 perature often rose to 35 C. Into this house was introduced 

 the soiled linen from beds that had been occupied by yellow 

 fever patients. A certain number of persons occupied this 

 house for 20 days, sleeping between bed-clothes that had been 

 soiled by the excrement and black vomit of yellow fever 

 patients. In spite of these conditions none of the persons 

 occupying the house became infected and the experiment has 

 been repeated several times with similar results. No matter 

 under what conditions of sanitation, etc., in the absence of 

 Stegomyia, nobody became infected with the disease. 



Finally, a house was constructed of the same dimensions 

 as the preceding, but well lighted and ventilated, so as to 

 present the best hygienic conditions. This house was rendered 

 mosquito-proof by wire gauze, and also was divided into two 

 halves by means of a partition of the same material. On one 

 side the persons occupying the room were exposed to the same 

 conditions as in the preceding experiment, namely, sleeping 

 between the soiled bed linen from yellow fever patients, etc. 

 In the other half only carefully sterilized material was allowed 

 to enter but, in addition, there were introduced 15 mosquitoes 

 that had fed, at least 12 days previously, on patients at the 



