Page:Popular Science Monthly Volume 26.djvu/666

 same time to protect them from the action of the vapors, the following plan, also indicated in the section diagram, is adopted. The door or entrance into the lethal chamber is a slide like the sash of a window. It is placed between two strong uprights, and is balanced by a weight and pulley in each, so that it can be opened and closed with the greatest rapidity. Behind this sliding door there is placed what I call the



shield or block; a framework of wood with four large metal valves, two opening inward, two outward. The shield is fixed on a base with four little wheels, and runs easily up or down the chamber. When the sliding door is raised, the movable valved shield is in position half a foot within the chamber, and cuts off all escape of vapor. The workmen thus have time to push the cage leisurely, after the door is raised, into the chamber, until the end of the cage touches the screen. This effected, they push the cage in a few seconds into the lethal atmosphere, the shield running before it, and then the door is slided down into its place. When all is nicely adapted, a very few seconds are required to introduce the cage and close the sliding or entrance door. When the cage is drawn out the shield is drawn out with it, by means of a cord which is attached to it, and which runs under the cage.

The last requirement which had to be met was the means of knowing when the narcotized animals had ceased to breathe. To get at this fact, the test of hearing was found to be the best. There is inserted into the chamber on one side a long stethoscope, made of bamboo; the mouth of this tube—of trumpet-shape—is in the center of the chamber, just above the cage, when that is in place. The outer part, or ear-piece, of the tube stands out four inches on the outside, and is closed when not being used, by a solid plug. On listening through this tube, the continued breathing of even a single animal can be detected, and the operators are enabled to determine if it be proper to increase the strength of the narcotic atmosphere, or to stop it.

In Fig. 4 will be seen best a description of the cage in which the animals are collected before being put into the lethal chamber. It is made of a wooden framework, with light iron side-bars. It has two sliding doors at the sides, two at one end, and one at the top. It can