204- RESPIRATION. 



vitating in the bronchiae. The diaphragm and intercostal muscles 

 ceasing to act, the substance of the lungs exerts its elasticity 

 with effect, recovers its former dimensions, and drives out the 

 additional volume of air just admitted, and the passive diaphragm 

 follows the shrinking substance of the lungs, offering, from its 

 relaxation, no resistance to the atmosphere pressing on the 

 surface of the abdomen. Thus expiration is produced. The 

 muscular power of the diaphragm and intercostal muscles is 

 far greater than the elastic power of the lungs, and therefore, 

 when exerted overcomes it, producing inspiration : but, ceasing 

 to be exerted, the elastic power gains efficiency, and produces 

 expiration. 



To the elastic, Reisseisen adds the muscular, contraction of the 

 bronchial ramifications and cells. " Thorace ampliato, ae'r vacuum 

 in pulmone spatium occupat, victisque Jibris^ fistulam spiritalem 

 quaquaversum extendit, ultra modum, quo quiescit, explicari 

 coactam, unde fibrae clastica resilire, circulares sese contrahere 

 nituntur, quo fit ut desidente thorace omnes simul ad expellendum 

 spiritum vires intenduntur. Sunt autem, thoracis undique desi- 

 dentis pressio, turn fibrarum fistulam spiritalem in brevius contra- 

 hentium vis elastica, denique muscularium illam constringentium 

 irritabilitas. 



" The contractile power of the diaphragm (and intercostal 

 muscles), in conformity with the laws of muscular motion," says 

 Dr. Carson z , " is irregular, remitting, and sometimes altogether 

 quiescent. The elasticity of the lungs, on the other hand, is 

 equal and constant. The superior energy of the former is 

 balanced by the permanency of the latter. By the advantage 

 which the inferior power, from the uniformity of its operations, is 

 enabled to take of the remissions of its more powerful antagonist, 

 the ground which had been lost is recovered, and the contest 

 prolonged; that contest in which victory declaring on one side or 

 the other is the instant death of the fabric." 



In the common account of respiration, the elasticity and mus- 

 cularity of the lungs are unnoticed, and expiration is ascribed to 

 the elasticity of the cartilages of the ribs, and to the contractions 

 of the abdominal muscles emptying the lungs by pressure. Now, 

 according to Dr. Carson, in the first place, the elasticity (and 

 muscularity) of the lungs is of itself sufficient for the purpose ; in 



z 1. c. p. 223. 



