254 ENTOMOLOGY 



plete record was kept of the health of every subject; furthermore, ample 

 time was allowed for any possible development of the disease within the 

 camp before the experiments were begun. In short, the precautions 

 taken were so thorough that yellow fever never appeared in the camj 

 except at the will of the experimenters. 



Harmlessness of Fomites. In a specially constructed building, 

 which was screened against mosquitoes and purposely ill-ventilated, 

 volunteers slept for twenty nights with bedding and clothing that had 

 been contaminated by yellow fever patients, and tried in every other 

 way to contract the disease, if possible, from the fomites, or belongings, 

 of fever subjects; yet the health of these volunteers remained unimpaired: 

 though they were not immunes, for some of them were subsequently 

 infected artificially by means of mosquitoes. 



Transmission by Transfusion. It was found that the disease coul( 

 be conveyed to non-immunes by the subcutaneous injection of blood 

 taken from the veins of patients during the first three days of the disease. 



Experiments with Mosquitoes. These experiments were made at 

 a time of the year when there was the least chance of acquiring the dis- 

 ease naturally. The mosquitoes used were bred from the eggs and kept 

 active by being maintained at a summer temperature. From time to 

 time some of them were taken away to a yellow fever hospital, fed on the 

 blood of patients and applied to non-immunes in the camp at varying 

 intervals from the time of feeding. The occupants of the camp were, of 

 course, protected carefully from accidental mosquito bites. When a 

 subject came down with yellow fever as the result of an experimental 

 inoculation he was at once removed from the camp to a yellow fever 

 hospital. 



In a mosquito-proof building a single room was divided into two 

 compartments simply by means of a partition of wire netting. On one 

 side of the screen infected mosquitoes were liberated; and a brave non- 

 immune, who had been in quarantine for thirty-two days, entered the 

 compartment, allowed himself to be bitten several times, and contracted 

 the disease. In the opposite compartment, free from mosquitoes, non- 

 immunes slept with perfect safety ; and the other room became harmless 

 as soon as the mosquitoes were removed. 



In another experiment the subject acquired the disease by thrusting 

 his arm into a jar of infected mosquitoes. Eighteen non-immunes were 

 inoculated, ten of them successfully. It was demonstrated that yellow 

 fever is transmitted by the bite of a mosquito, and in no other way 

 except by the artificial injection of diseased blood. The mosquito can 



