RELATIVE TIME OF INSPIRATION AND EXPIRATION 281 



produced by the movements of the chest, are communicated to a recording 

 tambour. This principle is applied in a modified form in Marey's pneumo- 

 graph, figure 231. 



The variations of intrapleural pressure may be recorded by introducing a 

 cannula into the pleural or pericardial cavity. The cannula should be pre- 

 viously connected with a mercury or other form of manometer by tubing 

 filled with physiological saline. 



Tambour. 

 Ivory button. 



Tube to commu- 

 nicate with re- 

 cording tam- 

 bour. 



Ball to fill appa- . 

 ratus -with air. 



FIG. 233. Stethometer. (Burdon-Sanderson.) 



Finally, it has been found possible in various ways to record the diaphrag- 

 matic movements. This can be done by inserting a receiving tambour into 

 the abdomen below the diaphragm, by the insertion of needles into different 

 parts of the diaphragm and recording the movement of the free ends of needles 

 about the fulcrum formed where the chest wall is pierced, or by recording the 

 contraction of isolated strips of the diaphragm directly. These records all 

 give an accurate picture of the movements of the diaphragm. 



The Relative Time of Inspiration and Expiration and the Respira- 

 tory Movement. The acts of inspiration and expiration take up, under 

 ordinary circumstances, a nearly equal time. The time of inspiration, 

 however, especially in women and children, is a little shorter than that of 

 expiration, and there is commonly a very slight pause between the end of 

 expiration and the beginning of the next inspiration, see figure 232. The 

 ratio of the respiratory rhythm may be thus expressed: 



Inspiration 6 



Expiration 7 to 8 



Pause Very slight 



