Measurement of the respiratory volumes of laboratory animals.

In the last few years a tremendous amount of study has been directed toward the etiology and pathogenesis of respiratory disease. Quantitative studies of respiratory infection by t.he cloud chamber method require that the respiratory volume of test. animals be known in order to calcu late the dose of agent used. Because data in the literature on respiratory volume of laboratory animals are very scanty, a comprehensive study of this subject was undertaken. LMETHODS. The various methods used for the determination of respiratory volume may be classed under five different headings: 1, respirograph method (5, 7) ; 2, valve method (2) ; 3, air flow methods (1, 8) ; 4, indirect calculation from 02 consunlpbion (4, 9) ; and 5, an acoustic respirograph method (6). Two valve methods and one modified respirograph method have been used in the investigations described in this paper. A. Valve methods. The valves used were of delicate construction utilizing very minute thin rubber discs, which were hinged loosely over the tips of polished glass inlet and outlet These valves were tubes. then connected directly bY means of a glass seal either to a tight-fitting headpiece or to a tracheal cannula. Collect.ion of air from the outlet valve was accompl ished by the two methods shown in figures 1 and 2. When the collection apparatus shown in figure 1 is employed, the expired air enters via the rubber tube attached to the top of th.? mercury-filled collecting chamber, which may be connected to the water 01 mercuqy man the stopcock .ometer on eith er side of the co1 letting column. By manipulating at the bottom of the collecting column, mercury is allowed to fall at a rate which will exactly equalize that of the expired air and maintain pressure within the chamber at exactly zero. By measuring the fall of the mercury column for one minute while the pressure within the chamber is maint.ained at atmospheric pressure, the respiratory volume per minute may be measured directly. In using this method, the only obstruction to the flow of air is a verv c slight back pressure from the valves. The second apparatus for collecting the expired air is shown diagrammatically in figure 2. It is so constructed that no water can flow from the upper siphon jar into the lower jar until an equal volume of air is introduced into the air space above the wat,er in the upper jar. Special precautions have been taken in the design of this apparatus so that the pressure against which the animal must