354 RESPIRATION [CH. XXIV. 



chest-walls, is returned as an expiratory effort when the muscles are 

 relaxed. This elastic recoil of the chest and lungs is sufficient, in 

 ordinary quiet breathing, to expel air from the lungs in the intervals 

 of inspiration, and no muscular power is required. In all voluntary 

 expiratory efforts, however, as in speaking, singing, blowing, and the 

 like, and in many involuntary actions also, as sneezing, coughing, etc., 

 something more than merely passive elastic power is necessary, and 

 the proper expiratory muscles are brought into action. By far the 

 chief of these are the abdominal muscles, which, by pressing on the 

 viscera of the abdomen, push up the floor of the chest formed by the 

 diaphragm, and by thus making pressure on the lungs, expel air from 

 them through the trachea and larynx. All muscles, however, which 

 depress the ribs, must act also as muscles of expiration, and therefore we 

 must conclude that the abdominal muscles are assisted in their action by 

 the interosseous part of the internal intercostals, the triangularis sterni, 

 the serratus posticus inferior, and quadratics lumborum. When by 

 the efforts of the expiratory muscles, the chest has been squeezed to 

 less than its average diameter, it again, on relaxation of the muscles, 

 returns to the normal dimensions by virtue of its elasticity. The 

 construction of the chest-walls, therefore, admirably adapts them for 

 recoiling against and resisting as well undue contraction as undue 

 dilatation. In the natural condition of the parts, the lungs can 

 never contract to the utmost, but are always more or less " on the 

 stretch," being kept closely in contact with the inner surface of the 

 chest walls. 



Methods of recording Respiratory Movements. 



The movements of respiration may be recorded graphically in several ways. 

 One method is to introduce a tube into the trachea of an animal, and to connect 

 this tube by some gutta-percha tubing with a T-piece introduced into the cork of a 

 large bottle, the other end of the T having attached to it a second piece of tubing, 

 which can remain open or can be partially or completely closed by means of a screw 

 clamp. Into the cork is inserted a second piece of glass tubing connected with a 

 Marey's tambour by suitable tubing. This second tube communicates any altera- 

 tion of the pressure in the bottle to the tambour, and this may be made to write on 

 a recording surface. 



There are various instruments for recording the movements of the chest by 

 application of apparatus to the exterior. Such is the stethograph of Burdon- 

 Sanderson (fig. 329). This consists of a frame formed of two parallel steel bars 

 joined by a third at one end. At the free end of the bars is attached a leather strap, 

 by means of which the apparatus may be suspended from the neck. Attached to 

 the inner end of one bar is a tambour and ivory button, to the end of the other an 

 ivory button. When in use, the apparatus is suspended with the transverse bar 

 posteriorly, the button of the tambour is placed on the part of the chest the move- 

 ment of which it is desired to record, and the other button is made to press upon 

 the corresponding point on the other side of the chest, so that the chest is, as it 

 were, held between a pair of callipers. The tambour is connected by tubing and a 

 T-piece with a recording tambour and with a ball, by means of which air can be 

 squeezed into the cavity of the tambour. When in work the tube connected with 

 the air ball is shut off by means of a screw clamp. The movement of the chest is 

 thus communicated to the recording tambour. 



