With this idea in view they selected a spot a mile or more from the military camp, which was well isolated and had no habitations near it. They agreed that if they established an experimental station here and kept their patients in such a way that there was no possibility of their getting out and contracting the disease elsewhere, then the results obtained in this station would be due to measures taken there. They already had their stegomyia mosquitoes which they had reared from the eggs procured from Dr. Finlay. These mosquitoes they took to the hospitals in Havana, and allowed them to bite people sick with yellow fever. In the course of time the Board found that the mosquito to become infected with this disease must bite the sick human being within the first three days of his disease. This was a singular and unexpected phenomenon, and is explained in this way. The mosquito injects the yellow-fever parasite into the blood of the human being; these parasites at once commence ejecting toxins into the blood in which they are circulating; these toxins irritate the human cells with which the poisoned blood comes in contact and they begin to throw into the blood circulation antitoxins. By the end of the third day these antitoxins have become so concentrated in the blood that they always kill the yellow-fever parasite, and after the third day no yellow-fever parasites remain in the human body. Yellow fever is a very fatal disease, and on the average kills the patient on the sixth or seventh day. Why then does death occur in yellow fever if on the average the patient lives to the sixth or seventh day, and yet always by the end of the third day the yellow-fever parasites have been routed and destroyed in the great battle which has taken place between them and the body cells? Dr. Reed established this fact by finding that mosquitoes which had bitten a patient more than three days after the patient had developed yellow fever, did not convey the disease to the non-immune when he attempted to infect these non-immunes with such mosquitoes. On the other hand, he found that he was almost always able to give these non-immunes yellow fever when he used mosquitoes which had bitten the man sick with yellow fever within the first three days of his symptoms.