it was cooled without any other artificial means, so as never to raise the chamber above summer heat; it was produced cheaply; and it afforded such simple action that any workman could at once learn to use it. Another useful result springing from the employment of this stove was, that it enabled me to diffuse other narcotics into the chamber, by merely allowing the warm gas proceeding from the stove to pass over a porous surface, charged with the narcotics, on its way into the chamber.
To apply the narcotic gas or vapor, it is necessary to have a closed place in which the animals are exposed to the narcotic, and another place in which they are collected preparatory to being subjected to the narcotism. This implies what I have called the lethal chamber, and a cage. At Battersea, it was necessary to have an apparatus large enough to narcotize as many as one hundred dogs at a time. It was, therefore, essential to have a large lethal chamber, and one that was strong and effectively constructed. I noted down at the beginning the following requirements, all of which I had calculated out of a series of preliminary studies, and constructed on a small working scale.
1. The chamber, of whatever substance built, must be so constructed that its interior shall not be subject to great variations of temperature. This I knew to be very important, since, in observing the action of narcotic vapors on the human subject, I had learned that humidity and cold materially interfere with their quick action, while dryness and warmth favor such action. In a lethal receptacle, such as was being constructed, there could be no certainty whatever, unless the temperature and dryness were at all times uniform.
2. It was necessary so to construct the chamber that sufficient but not an excess of room should be allowed in it for the expansion of the gases introduced. It might seem at first sight, and before inquiry was instituted, that the more the space within the chamber was reduced the quicker would be the effect. This, however, is not practically the fact. In order to secure perfect diffusion of the narcotic atmosphere, the space to be filled with it must be about one eighth greater than is absolutely required for a cage, fully charged with the animals that have to be killed.
3. Much care is required in connecting the stove with the chamber, so as to make sure of equal diffusion of the gases or vapors through the inclosed space. Unless this equal diffusion is rendered effective, some of the animals are more exposed to the vapors than others, and the effects are irregular, which is as bad a result as could possibly be obtained.
4. It was essential to provide that a sufficient quantity of the narcotic should be introduced before and for a brief period after the introduction of the animals.
5. It was requisite to invent a plan by which the chamber could be kept completely closed until the precise moment when the animals
