266 POPULAR SCIENCE MONTHLY. 



mile distant. Every person in camp was rigidly protected from acci- 

 dental mosquito bites, and not in a single instance did yellow fever 

 develop in the camp, except at the will of the experimenters. The 

 experiments were conducted at a season when there was the least chance 

 of naturally acquiring the disease, and the mosquitoes used were kept 

 active by maintaining them at a summer temperature. 



A completely mosquito-proof building was divided into two com- 

 partments by a wire screen partition ; infected insects were liberated on 

 one side only. A brave non-immune entered and remained long 

 enough to allow himself to be bitten several times. He was attacked 

 by yellow fever, while two susceptible men in the other compartment 

 did not acquire the disease, although sleeping there thirteen nights. 

 This demonstrates in the simplest and most certain manner that the 

 infectiousness of the building was due only to the presence of the 

 insects. 



Every attempt was made to infect individuals by means of bedding, 

 clothes and other articles that had been used and soiled by patients 

 suffering with virulent yellow fever. Volunteers slept in the room 

 with and handled the most filthy articles for twenty nights, but not a 

 symptom of yellow fever was noted among them, nor was their health 

 in the slightest degree affected. Nevertheless, they were not immune 

 to the disease, for some of them were afterward purposely infected by 

 mosquito bites. This experiment indicates at once the uselessness of 

 destroying valuable property for fear of infection. Had the people of 

 the United States known this one fact a hundred years ago, an enor- 

 mous amount of money would have been saved to householders. 



Besides the experimental cases caused by mosquito bite, four non- 

 immunes were infected by injecting blood drawn directly from the 

 veins of yellow fever patients in the first two days of the disease, thus 

 demonstrating the presence of an infectious agent in the blood at this 

 early period of the attack. Even the blood serum of a patient, passed 

 through a bacteria-proof filter, was found to be capable of causing 

 yellow fever in another person. 



The details of the experiments are most interesting, but it must 

 here suffice to briefly sum up the principal conclusions of this admirable 

 board of investigators of which Eeed was the master mind : 



1. The specific agent in the causation of yellow fever exists in the 

 blood of a patient for the first three days of his attack, after which 

 time he ceases to be a menace to the health of others. 



2. A mosquito of a single species, Stegomyia fasciata, ingesting the 

 blood of a patient during this infective period is powerless to convey 

 the disease to another person by its bite until about twelve days have 

 elapsed, but can do so thereafter for an indefinite period, probably dur- 

 ing the remainder of its life. 



3. The disease can not in nature be spread in any other way than 



