This last danger need scarcely be apprehended, as, after the pressure gage indicates the force of expansion required, the further generation of the gas can be entirely stopped, until the vacuum created by the outflow of liquid needs to be replaced by a new supply of gas. For it is a fact well understood, that the force of expansion of the generating power decreases in the same proportion as the volume of the liquid is diminished, thereby causing a greater vacuum in the apparatus. The inside of the apparatus is thickly coated with lead, as that metal is not sensibly acted on by either muriatic or sulphuric acid, except at very high temperatures. The jet or stream of liquid can be regulated by a screw cock, attached to the neck of a metallic tube reaching to the bottom of the apparatus, inside, and provided at its inner extremity with a perforated bulb, which, acting as a filter, prevents any impurity or sediment from finding its way into and stopping the circulation of the fluid through the arterial system; at the same time it prevents any excessive amount of pressure upon the rubber tube five or six feet in length, which is connected with the delivery tube outside, and at the end of which the nozzle is attached. The nozzle or cannula itself is a very important part of the apparatus, and is of a peculiar shape; it consists of a thin copper tube about eight inches in length and a little over an eighth of an inch in diameter; it is to be inserted at full length, or nearly so, into the artery to be injected, as by doing so it meets a point where the walls of the artery are strengthened by the surrounding tissues. The shape of the apparatus is that of an elongated cylinder, rounded off at both ends, resembling somewhat a soda fountain; it stands upright, upon four curved legs about four inches in height, and possesses a symmetrical and substantial appearance. The other apparatus—Ronsard’s—is about similar in construction, but the power exerted in forcing out the liquid is not gas, as in the former apparatus, but compressed air, forced into the body of the reservoir by means of a pump. The body of the apparatus consists of a cylinder holding about five gallons; this constitutes the reservoir containing the liquid to be injected. Outside of this cylinder and running alongside of it is the body of the pump. The pipe communicating the air forced inside the cylinder above the liquid enters the bottom of the reservoir, and, passing through the liquid, runs along the inner side of the vessel until it has reached a point almost to the top of the cylinder. In the center of the apex at the top of the cylinder is a small funnel connected to a pipe running inside of the apparatus; this pipe, which is furnished with a cock, is intended to conduct inside the apparatus the liquid poured in at the funnel; it will act also as a relief cock, should it be found necessary to relieve the pressure on the liquid.