American journal of physiology . rding lever of theaeroplethysmograph, which records at the same time the respiratorymovements as in previous experiments. The instrument was cali-brated and tested, being found ac-curate to a small fraction of oneper cent.^ Briefly then in all experimentsthe subject breathed through anair-tight mouthpiece from aconfined volume of air whichin all experiments was about 30litres. Valves separated the ex-pired from the inspired air. Thecarbon dioxid gradually accumu-lated in the confined space, andthe oxygen gradually diminished,although at the end of none ofFigure
American journal of physiology . rding lever of theaeroplethysmograph, which records at the same time the respiratorymovements as in previous experiments. The instrument was cali-brated and tested, being found ac-curate to a small fraction of oneper cent.^ Briefly then in all experimentsthe subject breathed through anair-tight mouthpiece from aconfined volume of air whichin all experiments was about 30litres. Valves separated the ex-pired from the inspired air. Thecarbon dioxid gradually accumu-lated in the confined space, andthe oxygen gradually diminished,although at the end of none ofFigure 1. —Diagram of the essential parts ^^^^^^ experiments was the per-of the apparatus. A, mouthpiece with lip , , , ^• • ^ • J^^ 1 , .u fl n -A ^ u ( * 1 • centage of carbon dioxid in the and teeth flanges; B, side tube for takmg ° specimen of alveolar air; c, expiratory inspired air greater than 7 nor valve; D, 20-htre bottle; E, side tube to air that of the OXygen less than , F, of the aeroplethysmograph; G,. the water seal; H, inspiratory valve; K, knife edge; point. To make respiratory tracings ofthis kind from different individ- L, counterpoise; M, writing uals strictly comparable, the vol-ume of air used by each personshould be proportional to liis body weight. The tracings show, as mighthave been anticipated, that a man of 120 pounds weight lasts longer onthe same volume of air than one of 170 pounds. I regret that this pointescaped my attention until the experiments were almost completed;but careful tests by two of my students, Mr. Mercer Blanchard andMr. Charles M. O Connor, show that when the same subject uses ,30, and 40 Htres of air in different experiments, no feature of the 2 The aeroplethysmograph, valves for separating inspired and expired air, andthe counter have all been made in the shoji of the Physiological Laboratory of theUniversity of Virginia. While the construction of tliis apparatus for others mustbe secondary to the use of the s
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