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