Physiology and biochemistry in modern medicine . ions on laboratory an-imals the best type of recording instrument to connect with the respira-tory passages is the Gad or Krogh pneumograph. A body plethysmographas used in the case of man is shown in Fig. 109. All these instrumentsmust of course be calibrated, which is done by pouring a definite num- 304 THE RESPIRATION ber of of water from a graduate into a bottle with which the record-ing instrument is connected by tubing. The displacement of the writingpoint gives us the necessary data for standardization. The Intrapleural Pressure The
Physiology and biochemistry in modern medicine . ions on laboratory an-imals the best type of recording instrument to connect with the respira-tory passages is the Gad or Krogh pneumograph. A body plethysmographas used in the case of man is shown in Fig. 109. All these instrumentsmust of course be calibrated, which is done by pouring a definite num- 304 THE RESPIRATION ber of of water from a graduate into a bottle with which the record-ing instrument is connected by tubing. The displacement of the writingpoint gives us the necessary data for standardization. The Intrapleural Pressure The air which Ave have just been considering depends for its move-ment in and out of the air passages upon changes occurring on the outeraspect of the lungs in the space between them and the thoracic is called the intrapleural space. It does not really exist as anactual space in the living animal, for the visceral pleura which coversthe lungs is in accurate and intimate apposition with the parietal pleuraon the inner aspect of the Fig. 109. -Body plethysmograph for recording respiration. Priestley.) (From J. S. Haldane and J. G. If the thoracic Avails are punctured in a liATing animal or in one whichhas recently died, the air will rush into the thorax, the two layersof pleura separate, and the lungs collapse, causing temporarily a spaceto be formed betAveen the tAvo layers of pleura and indicating that acertain subatmospheric or negative pressure must exist in the intactthorax to preA^ent the lungs from collapsing. The degree of this nega-tiA-e pressure may be measured by connecting a tube and a manometerAvith the thoracic cavity. While the thorax is at rest, as in expirationor immediately after death, this pressure amounts to about -5 milli-meters.* On inspiration it increases to -10 millimeters. There are there-fore tAvo problems to be considered: (1) the cause of the negatiAre pres-sure in the quiescent thorax, and (2) the cause of the increase of thenegatiA-e
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