XII 



MECHANICS OF RESPIRATION 



425 



on the rotating cylinder (Tigerstedt), as shown, in Fig. 187. The chamber in 

 which the animal breathes must be entirely shut off when it is desired to 

 trace the progressive alterations in the respiratory movements due to 

 asphyxia (Luciani) ; otherwise it communicates with the outer air by a more 

 or less open tube, which allows the air within the bottle to be renewed when 

 required (Tigerstedt). In that case, however, the oscillations in the tracing 

 are not proportional with those of the intrapiilmonary pressure. 



The same effect may be obtained when the animal is breathing free 

 air, while enclosed within a hermetically sealed glass cylinder (Knoll). 

 A tube tied in the trachea, or fitting closely over the mouth and nostrils 

 of the animal, passes through one wall of the box and communicates with 

 the external air. The internal air of the box is connected by means of a 

 second tube with a recording tambour, and traces, like a plethysmograph, 

 the variations in the total volume of the animal, corresponding to the 

 inspiratory and expiratory movements. The simplest application of this 

 method is that of Bernstein, represented in Fig. 188. 



IX. In proportion as the negative intrathoracic pressure 

 increases or diminishes in consequence of the inspiratory and 

 expiratory movements, the 

 lungs dilate and retract 

 with the air that pene- 

 trates through the glottis 

 to the pulmonary passages, 

 where equilibrium of air 

 pressure is restored. 



Both in dilatation and 

 in retraction of the lungs 

 the two layers of the 

 pleura, visceral and parie- 

 tal, remain, as we have said 

 in constant contact. At the 

 same time they glide one over the other, because the cavity of the 

 thorax, owing to the action of the respiratory muscles, does not 

 dilate and contract equally in all its diameters, but undergoes 

 perceptible changes of form, particularly at the base, so that the 

 lungs (which must passively follow the excursions of the thorax) 

 also change their form in order to adapt themselves to the new 

 shape of the thoracic cavity (Bonders). 



The most immovable part of the lungs, which undergo the 

 least displacement, are the roots, the apices, the posterior border, 

 and that portion of their external surface which underlies the 

 lateral parts of the vertebral column ; the most mobile are those 

 farthest removed from the fixed parts, i.e. their inferior and 

 anterior borders, and the median surfaces. The movement of the 

 pleural layers, therefore, takes place specially in the longitudinal 

 direction from above downwards, and in the transverse direction 

 from behind forwards. 



Under normal conditions this movement can be distinguished 

 by percussion, which yields a clear, full sound in every part of the 



Fro. 188. Bernstein's pneumoplethysmograph or spiro- 

 graph. Hermetically sealed glass cylinder, in which 

 the animal breathes the external air freely from the 

 mask c and tube a. The rubber tube ft, communicating 

 with the inside of the cylinder, is connected withja 

 Marey's tambour and writing-lever. 



