MECHANICAL PHENOMENA OF RESPIRATION. 313 



junction being occupied by the heart (see Fig. 42, p. 143) ; 

 the cavity of the lungs contains : 1. All that portion of the 

 circulation called pulmonary, that is, the upper circle ; 2. The 

 point of junction of these two circles, viz., the heart ; and 3. 

 The lateral origins of the lower circle, or the summit of the 

 arterial and of the venous cone. The changes in intra- 

 thorncic pressure affect all these three portions. 



This influence is counteracted, however, in the case of the 

 circulation of the thorax, by the fact that the venous cone of 

 this circulation is subjected to the same variations, and 

 simultaneously, as the arterial cone; and as the differences of 

 intravascular pressure which produce the circulation remain 

 the same, no change in the circulation occurs; the circulation 

 is but slightly influenced, except by the more or less com- 

 plete expansion of the alveoli, which occasions a greater or 

 less permeability of the capillary vessels, or, in other words, 

 of the base of the pulmonary cone. 



The influence of respiration is much more sensibly felt in 

 the heart : an expiration made with force, as in any great 

 exertion, causes immense pressure upon the heart, and as the 

 coats of this cavity are thin, and easily compressed, a deform- 

 ation ensues. Weber has made experiments to show this, by 

 first making an extremely deep inspiration, and then very 

 forcible movements of expiration, the glottis being closed, 

 and the arms kept fixed against his sides. After the lapse of 

 a few seconds, a change is observed in the pulse, which becomes 

 slower, and, at length, ceases entirely ; if the ear is placed 

 over the chest, no sound is heard, whence we may infer that 

 the heart has ceased to beat. If 'the experiment be continued, 

 the person loses consciousness, and thus, in spite of himself, 

 returns to his original state of life and circulation. 



If, however, the person remains passive, the stoppage of the 

 heart continues, and may end in death ; this is probably the 

 case with persons who are squeezed to death in a turbulent 

 crowd, the outside pressure being continued even after syn- 

 cope has been produced. 1 In experiments or accidents of 

 this kind, the stoppage is not the same in all parts of the 



1 A case has been reported by the American editor (" Boston 

 Med. & Surg. Journal," Dec. 11, 1873, p. 577), in which a rup- 

 ture of the right auricle was caused by compression of the thoracic 

 walls. Another accident (reported in the " Gaz. Hebd.," March 

 27, 1871, p. 199, by MM. IJoubre and Charpentier) of compression 

 of the thorax between awheel and the ground, resulted also in the 

 rupture of the right auricle. 



