672 DISEASES CAUSED BY FILTRABLE VIRUS 



and the members of the commission only were allowed to go in and out. 

 All non-immunes who left the camp were prohibited from re-entering and 

 their places taken by other non-immune volunteers. During December, 

 five of the non-immune inmates were successfully inoculated with yel- 

 low fever by means of infected mosquitoes. During January and Febru- 

 ary five further successful experiments were made. Clinical observa- 

 tions were made by experienced native physicians, Carlos Finlay among 

 them, and the patients, as soon as they were unquestionably ill with 

 yellow fever, were removed to a yellow -fever hospital. This was done 

 to prevent the possibility of the disease spreading within the camp it- 

 self. The mosquitoes used for the experiments were all cultivated from 

 the larva and kept at a temperature of about 26.5 C. 



A further important experiment was now made A small house was 

 erected and fitted with absolutely mosquito-proof windows and doors. 

 The interior was divided by wire mosquito netting into two spaces. With- 

 in one of these spaces fifteen infected mosquitoes were liberated. Seven 

 of these had fed upon yellow-fever patients four days previously ; four, 

 eight days previously; three, twelve days previously; and one, twenty- 

 four hours previously. A non-immune person then entered this room 

 and remained there about thirty minutes, allowing himself to be bitten 

 by seven mosquitoes. Twice after this the same person entered the 

 room, remaining in it altogether sixty-four minutes and being bitten fif- 

 teen times. After four days this individual came down with yellow fever. 



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

 out 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 mosquito-proof 

 house was constructed. By artificial heating its temperature 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 

 shooL 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 contracted yellow fever. The same experiment was twice re- 

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



