RESPIRATION IN MAN 193 



action of the expiratory muscles. The erect posture neces- 

 sitates an increased action of the musculature of the belly wall 

 in order to balance the body, the ribs being thus more firmly 

 fixed than in the supine position ; with the assumption of the 

 supine position the musculature of the belly wall is relieved of 

 its postural function, thus lessening the strain on the ribs and 

 allowing them to move more freely. If expiration were an elastic 

 recoil uncontrolled by muscular action one would expect the thorax 

 to diminish simultaneously in all its parts ; this is not so, for ex- 

 piration like inspiration is a definite movement commencing in the 

 upper or lower part of the thorax and spreading gradually to the 

 rest. Those who regard normal expiration as a result of the elastic 

 recoil of the lungs cite as conclusive evidence of their opinion 

 those cases of fracture of the spine or section of the spinal cord 

 where the diaphragm is the sole respiratory muscle in action. In 

 such cases the writer has observed that the patient lies on the 

 back or turned somewhat on the left side ; the epigastric move- 

 ments are greater than normal ; pressure of the hand applied to 

 the epigastrium gives immediate distress and completely alters the 

 type of respiratory movement, the lower ribs being then raised 

 and the lower part of the chest expanded. Further, the writer 

 observed that the diaphragm in such cases is kept in a condition 

 of over-action ; in one case the diaphragm worked some 25 to 

 30 mm. below its normal level, thus compressing the abdominal 

 contents and obtaining a recoil from the weight and tension 

 of the abdominal viscera. To what extent the tonus of the 

 abdominal and thoracic musculature is lost in these cases has 

 not been determined. Mosso has shown that tone varies indepen- 

 dently of the contractibility, and that the abdominal musculature 

 possess a high degree of tone. The parietal layer of the peritoneum 

 is highly extensile and elastic to preserve its smoothness in the 

 various states of movement. 



THE RESPIRATORY VALUE OF THE ELASTICITY OP 

 THE THORAX 



The degree of elasticity of the living thorax has to be esti- 

 mated from experiments made on the dead. We now know, from 

 observations made by the use of X-rays, that the diaphragm is 



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