364 LUNGS AND PLEURJ^. 



The sighing sound heard on auscultation of the chest wall is louder than 

 that heard externally or over the region of the nostrils or larynx ; and it 

 seems to be reinforced, as though by the resonance of a large cavity with 

 thin metallic walls. Once or twice per minute, moreover, a sound may 

 be heard like that of dropping water. It is of a very special character, 

 resembling that produced by drops falling to the bottom of a hollow 

 metallic vase, and setting up prolonged vibration. 



As secondary symptoms the heart's action is accelerated, the number 

 of beats rising to 80 or even 120 or 130 beats per minute ; appetite is 

 lost ; slight tympanites develops as a result of rumination and eructa- 

 tion being suspended ; the peristaltic movements of the rumen are inter- 

 rupted, and constipation develops. 



Diagnosis. The diagnosis of pneumo-thorax is easy, and the con- 

 dition can scarcely be mistaken for any other except diaphragmatic 

 hernia; but the indications derived from percussion and auscultation 

 are so different in the two cases that they need not be further 

 emphasised. 



The task becomes more difficult, however, when an attempt is made 

 to identify the exact form of pneumo-thorax, for three principal varieties 

 are recognised. 



In open pneumo-thorax, the first and most frequent form, air passes 

 from the lung into the pleura at each inspiration, and flows back from 

 the pleural cavity towards the bronchus at each expiration. The intra- 

 pleural pressure is then approximately equal to the intra-bronchial 

 pressure, and undergoes similar oscillations. (It should be noted that 

 the aperture in the lung is seldom sufficiently large to establish an 

 absolute equality of pressure between the bronchus and the pleural 

 cavity. Eespiration, therefore, though very seriously impeded, generally 

 continues in a modified form.) 



In a second variety, termed "valvular pneumo-thorax," air passes 

 freely from the lung into the pleural cavity, but is unable to return 

 from that cavity towards the lung, because a flap of tissue acts as a 

 valve and closes the orifice at the commencement of expiration. As 

 soon as intra-pleural pressure rises above that of the inspiratory effort, 

 the valve remains permanently closed. 



In the third variety, called " closed pneumo-thorax," the orifice of 

 communication is obstructed by some mechanism, and the pleural sac 

 only contains a film of air. 



In practice, valvular pneumo-thorax is recognised by the movement 

 of the thoracic wall (which in open and closed pneumo-thorax remains 

 depressed), as well as by extreme intensity of the dyspnoea and attacks of 

 threatened suffocation. Closed pneumo-thorax, which is only a termina- 

 tion and a stage in the cure of open pneumo-thorax and of valvular 



