He had a small frame house built, fourteen by twenty feet, well screened-in with wire netting, so that mosquitoes could not get in or out. This building he had divided into two compartments by a partition extending down the center, made of wire netting, and it was known as the infected mosquito building. It was well ventilated. Most persons at this time believed that in some way the air conveyed yellow fever. Dr. Reed wished to show that this was not the case. He put two non-immunes in this building, one in each room. These two men breathed exactly the same air, and had exactly the same surroundings, with one single exception which I will in a moment point out. But they were entirely separated by the wire netting. He let them live and sleep in these rooms for several days, so as to demonstrate that there was no yellow-fever infection in the building. He then put fifteen infected stegomyia in one of the rooms; left the man in this room for thirty minutes, announcing that the room was now infected. He took the man out of this infected room, but left in the other room two men on the other side of the wire netting. He stated that the man who had stayed thirty minutes in the infected room would come down with yellow fever within three or four days, and that the other men, who were only separated from him by wire netting, and who breathed and were surrounded by exactly the same air, would not get sick. He explained that the only difference between the two rooms was that in the infected room, infection had been brought about by liberating there fifteen stegomyia mosquitoes which had previously bitten patients sick of yellow fever. The man from the infected room was on the afternoon of the same day again placed in this room for twenty minutes, and on the following day he was a third time put in the room for fifteen minutes. On the first visit he was bitten by seven mosquitoes; on the second, by five; on the third, by three. At the end of the fourth (Christmas) day, Reed showed the man from the infected room down with yellow fever, and the men who had lived and slept in the other room, separated only by wire netting, perfectly well. He called attention to the fact that the only difference in the exposure of these men was that the sick man had been in a room for thirty minutes, with fifteen infected stegomyia mosquitoes. He claimed that this was a demonstration that the female stegomyia mosquito could transmit yellow fever, and that the atmosphere alone could not. Many of the visitors to Dr. Reed’s camp were clinically familiar with this disease, and the case was sufficiently marked to be easily recognized by all as being a case of yellow fever.