GENERAL STRUCTURE OF THE RESPIRATORY ORGANS. 369 



for then the pressure on the exterior of the lungs will be increased, the mer- 

 curv in the arm (c) of the manometer will descend, and, aided by their own 

 elasticity, the lungs will contract upon and drive out the air contained within 

 their cavities. 



288. The complete dependence of the expansion of the Lungs upon the 

 enlargement of the cavity of the chest, is well shown by the effect of admis- 

 sion of air into the pleura 1 cavity. When an aperture is made on either side 

 (as by removing the finger from the orifice of the tube a in the apparatus 

 represented in Fig. 161), so that the air rushes in at each inspiratory move- 

 ment, the expansion of the lung on that side is diminished, or entirely pre- 

 vented, in proportion to the size of the aperture. If air can enter through 

 it more readily than through the trachea, an entire collapse of the lung takes 

 place ; and by making such an aperture on each side, complete asphyxia is 

 produced. But if it be too small to admit the very ready passage of air, 

 the vacuum produced by the inspiratory movement is more easily filled by 

 the distension of the lungs, than by the rush of air into the pleural cavity ; 

 so that a sufficient amount of change takes place for the maintenance of life. 

 This is frequently observed in the case of penetrating wounds of the thorax, 

 in the surgical treatment of which it is of great importance to close the aper- 

 ture as completely as possible ; when this has been accomplished the air that 

 had found its way into the cavity is soon absorbed, and the lung resumes its 

 full play. Where one lung is obstructed by tubercular deposit, or is prevented 

 in any other way from rightly discharging its function, an opening that freely 

 admits air into the pleural cavity of the other side is necessarily attended 

 with an immediately fatal result; and in this manner it not unfrequently 

 happens that chronic pulmonary diseases suddenly terminate in Asphyxia, a 

 communication being opened by ulceration between a bronchial tube and the 

 cavity of the thorax. 



289. Of the Respiratory Movements. Every complete act of respiration 

 may be divided into 1, Inspiration ; 2, Expiration. 1 M. Marey 2 has con- 

 structed an instrument by which the movements of respiration can be regis- 

 tered, and to which he has applied the term pneumograph or atmograph ; it 

 consists of a spiral spring inclosed in a thin caoutchouc cylinder, the ex- 

 tremities of which are connected by a band passing round the body. A 

 lateral tube places the interior of the cylinder in communication with the reg- 

 istering apparatus, and the following cut (p. 370) shows a tracing taken from 

 a healthy subject. In ordinary tranquil breathing (especially in children), 

 the action of the diaphragm is alone nearly sufficient to produce the neces- 

 sary exchange of air, and this muscle is consequently the chief iuspiratory 

 agent; but when a full inspiration is required, the cavity of the chest is 

 dilated laterally and antero-posteriorly, as well as inferiorly. 3 The enlarge- 

 ment of the chest in both these directions is effected by the elevation of the 



1 The pause which was admitted by Vierordt and others to occur between Expira- 

 tion and Inspiration, has been shown by Riegel (Wurzburg. Med. Gesell., Bd. vii, 

 1867, p. 321), with a self-registering apparatus, not to be present at least when the 

 body is in a horizontal position. Sibson, Vierordt, and others believe they have 

 proved that the duration of the inspiration is to that of expiration as 10: 14 in the 

 child, female, and old person, and as 10: 1'2 in the adult male; but these statements 

 hardly accord with the tracing shown on the next page. See Sibson in Med.-Chir. 

 Transact., vol. xxxi, and Medical Anatomy. 



2 Kevue des Cours Sciont , 1807, p. 726. 



3 Bert (Lecons, p. 352) has clearly shown by tracings with his Tambour pour re- 

 cueillir les Mouvements du Thorax, or Pneumograph, that in the dog the diaphragm 

 in contracting causes the 6th and lower ribs to rise, and thus to increase the trans- 

 verse diameter of the chest; whilst, on the contrary, the 5th and upper ribs tend to 

 descend and diminish the transverse diameter. 



