A Multiple-Chamber Respiration Apparatus for Rats and Other Small Animals

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Abstract
A multiple-chamber, closed-circuit respiration apparatus is described, with which one person can measure simultaneously the gaseous metabolism of four different animals in periods as short as one hour or, if desired, can study only one or two animals at a time. The apparatus is comprised of four individual units. Each unit consists of a respiration chamber, a ventilating rotary blower, a spirometer serving as an expansion chamber and also as a reservoir for the supply of oxygen, and a container for sodalime, in which the carbon dioxide is absorbed from the ventilating air current. Oxygen is introduced into the spirometer from a pump of known volume. From the recorded time which has elapsed during the absorption of this known volume of oxygen by the animal, and from the records of pump and chamber temperatures and atmospheric pressure, can be calculated the volume of oxygen consumed at 0°C. and 760 mm. per hour. Slight changes in the absorber system make it possible to measure also the carbon-dioxide production and hence the respiratory quotient. Each chamber is provided with a device for the graphic registration of activity. The water vapor in the air of the closed system is removed by fused calcium chloride placed in a tray on top of the animal's cage inside the chamber. The four individual units are compactly mounted on a table, with separate bases for the spirometers, the respiration chambers, and the blowers, so that readjustment of the different parts may be readily made, when desired. The four blowers are immersed in oil in a metal box and are driven by a common shaft, with suitable gears, actuated by an electric motor outside the box. An electric resistance under the metal base of each chamber and asbestos partitions between the chambers aid in controlling the temperature inside the chambers. The accuracy of the apparatus has been demonstrated by an alcohol check test, in which a small flame was successfully kept burning to produce carbon dioxide at a rate only 15 per cent greater than the rate of carbon-dioxide production by a single, adult, albino rat. General tests for tightness of the apparatus are also described. This multiple-chamber system lends itself to a study of animals ranging in size from a rat of 60 grams to a giant rat of 600 grams and to the larger sizes of pigeons. Two apparatus of this type have been in constant use since 1927 in cooperative investigations on rats and pigeons.

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