CH. xxiv.] STETHOGRAPHS. 353 



tube the variations of the pressure of air in the bag produced by the 

 movements of the chest are communicated to a recording tambour. This 

 apparatus is a simplified form of Marey's stethograph (fig. 320). 



The variations of intrapleural pressure may be recorded by the introduction 

 of a cannula into the pleural cavity, which is connected with a mercurial 

 manometer. 



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

 phragmatic movements by the insertion of an elastic bag connected with a 

 tambour into the abdomen below it (phrenograph), by the insertion of 

 needles into different parts of its structure, or by recording the contraction 

 of isolated strips of the diaphragm. Such a strip attached in the rabbit to 

 the xiphisternal cartilage may be detached, and attached by a thread to a 

 recording lever. This method was largely used by Head ; this strip serves 

 as a sample of the diaphragm. 



Fig. 322 shows a tracing obtained in this way ; but in tracings taken with 

 a stethograph, or any of the numerous arrangement of tambours which are 

 applied -to the chest-walls of men and animals, the large up-and-down 

 strokes due to the respiratory movements have upon them smaller waves due 

 to heart-beats. 



The acts of expansion and contraction of the chest take up 

 under ordinary circumstances a nearly equal time. The act of 

 inspiring air, however, especially in women and children, is a little 

 shorter than that of expelling it, and there is commonly a very 

 slight pause between the end of expiration and the beginning 

 of the next inspiration. The respiratory rhythm may be thus 

 expressed : 



Intpiratwn . . . . . . . 6 



Erplratlur^ 7 or 8 



A very slight pauae. 



If the ear be placed in contact with the wall of the chest, or be 

 separated from it only by a good conductor of sound or stetho- 

 scope, a faint respiratory or vesicular murmur is heard during 

 inspiration. This sound varies somewhat in different parti; being 

 loudest or coarsest in the neighbourhood of the trachea and large 

 bronchi (tracheal and bronchial breathing), and fading off into a 

 faint sighing as the ear is placed at a distance from these (vesi- 

 cular breathing). It is best heard in children, and in them a 

 faint murmur is heard in expiration also. The cause of the 

 vesicular murmur has received various explanations ; but most 

 observers hold that the sound is produced by the air passing 

 through the glottis and larger tubes, and that this sound is 

 modified in its conduction through the substance of the lung. 

 The alterations in the normal breath sounds, and the various 

 additions to them that occur in different diseased conditions, can 

 only be properly studied at the bedside. 



Respiratory movements of the Nostrils and of the Glottit. 

 During the action of the muscles which directly draw air into the 



K.I'. A A 



