MECHANISM OF RESPIRATION. 97 



ing the abdominal organs downward. The ribs rise by the 

 contraction of numerous muscles ; at the same time with the 

 sternum, which is carried forward, the intercostal spaces en- 

 large, and the chest is developed in all its dimensions, verti- 

 cally, antero-posteriorly, and transversely. In expiration, the 

 inspiratory muscles relax, and others, especially those of the 

 abdomen, lower the ribs and the sternum by contracting the 

 chest; while the lungs, distended by the air inspired, collapse 

 under the pressure of the thoracic walls and their own proper 

 elasticity. The experiments of Duchenne of Boulogne tend 

 to prove that this contraction of the lungs is due to the 

 muscular fibres which accompany the bronchia down to their 

 minutest ramifications. 



Nearly all the inspirations are effected by the movements 

 of the diaphragm and the inferior ribs only. From time to 

 time a deeper and more complete inspiration causes the 

 thorax to rise, not simultaneously but successively at the base, 

 then at the apex. In the first case the respiration is dia- 

 phragmatic; when the lower and middle ribs are raised it is 

 termed lateral; and lastly, when the first rib and clavicle take 

 part in the movement, it is costo-superior or clavicular. In 

 diaphragmatic respiration, as M. Mandl has observed, the 

 larynx is immovable, the inspiration is easy, without effort, 

 and permits exertion in singing or in gymnastics for a long 

 time and without fatigue. On the contrary, persons who 

 respire principally by the upper ribs are easily fatigued, and 

 very soon out of breath. This is seen in women when the 

 corset compresses the base of the chest, and in singers who 

 adopt, on erroneous principles, the bad habit of clavicular 

 respiration. In this last method of inspiration the larynx is 

 drawn down by the contraction of the external muscles, and 

 its action becomes painful. The effort of the inspiratory 

 muscles rapidly induces fatigue, and the inspiration, always 

 incomplete, becomes also more frequent. Diaphragmatic 

 respiration is practised by mountaineers, gymnasts, and skilful 

 singers a habit induced either by instinct, or a well-directed 

 education. 



The respiratory movements are not completely under the 

 control of the will. It is not possible long to suppress the 



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