240 ENTOMOLOGY 



Transmission by Transfusion. It was found that the disease 

 could 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 Mosquitos. 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 egg 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 

 obtain infected blood from a patient during only the first three days of 

 his disease; in other words, the patient is no longer a menace to other 

 persons after three days from the time when he comes down with yellow 

 fever, which is from three to six days after the bite. 



After biting a patient the mosquito cannot convey the infection until 

 at least twelve days have elapsed; thereafter it can transmit the disease 

 for certainly six weeks and possibly eight weeks. 



Dr. James Carroll allowed himself to be bitten by an infected mos- 

 quito and consequently suffered a severe attack of yellow fever. He 

 recovered from this, but was left with an affection of the heart from 

 which he died in 1907. 



Dr. Lazear failed to acquire the disease artificially, early in the course 



