YELLOW FEVER AND THE LEPTOSPIRA 877 



gether sixty-four minutes and being bitten fifteen times. After 

 four days this individual came down with yellow fever. 



In the other room two non-immunes slept for thirteen nights 

 without any evil results whatever. 



It now remained to show that mosquitoes were the sole means 

 of transmission and to exclude the possibility of infection by contact 

 with excreta, vomitus, or fomites. For this purpose another mos- 

 quito-proof house was constructed. By artificial heating its tem- 

 perature was kept above 32.2 C. and the air was kept moist by 

 the evaporation of water. Clothing and bedding, vessels, and eating 

 utensils, soiled with vomitus, blood, and feces of yellow-fever 

 patients were placed in this house and three non-immune persons 

 inhabited it for twenty days. During this time they were strictly 

 quarantined and protected from mosquitoes. Each evening, before 

 going to bed, they unpacked and thoroughly shook clothing and 

 bedding of yellow-fever patients, and hung and scattered these 

 materials about their beds. They slept, moreover, in contact with 

 linen and blankets soiled by patients. None of these persons con- 

 tracted yellow fever. The same experiment was twice repeated by 

 other non-immunes, in both cases with like negative results. 



All of the non-immunes taking part in these experiments were 

 American soldiers. Four of them were later shown to be susceptible 

 to yellow fever by the agencies of mosquito infection or blood- 

 injection. 



The results obtained by the investigations of this commission 

 may be summarized, therefore, as follows: 



Yellow fever is acquired spontaneously only by the bite of the 

 Stegomyia fasciata. It is necessary that the infecting insect shall 

 have sucked the blood of a yellow-fever patient during the first 

 four or five days of the disease, and that an interval of at least 

 twelve days shall have elapsed between the sucking of blood and 

 the reinfection of another human being. Sucking of the blood of 

 patients advanced beyond the fifth day of the disease does not seem 

 to render the mosquito infectious, and at least twelve days are 

 apparently required to allow the parasite to develop within the 

 infected mosquito to a stage at which reinfection of the human 

 being is possible. 



The results of the American Commission were soon confirmed by 

 Guiteras 5 and by Marchoux, Salimbeni, and Simond. 6 These latter 



5 Guiteras, Eev. d. med. trop. Jan., 1901, and Am. Med., 11, 1901. 

 * Marchoux, Salimbeni, and Simond, Ann. de Tinst. Pasteur, 1903. 



