NATUKE. 517 



The contractile tissue of the king, represented by the en- 

 circhng invoknitary muscles of the mmute air-tubes, and 

 which functionally are subservient to the expulsion of the air 

 from the lungs, are dependent for their motor energy on the 

 integrity of the nerve-centres and on the correctness of im- 

 pressions conveyed to or from these centres. The difference 

 in the character and extent of impediment in the execution of 

 expiration met with in different stages of the disease may be 

 accounted for by supposing that at first these muscular struc- 

 tures of the minute bronchi are merely spasmodically con- 

 tracted; that at a more advanced stage of the disease they 

 become structurally altered, apparently atrophied, with certain 

 changes of a degenerative character. 



This paralysis of the muscular tissue of the air-tubes, or the 

 arrest of their contractile action, induced by gastric irritation, 

 will, in process of time, from the continued action of accessory 

 agencies, as the compression carried out by the abdominal 

 muscles operating on the air retained in the pulmonary alveoli, 

 and aided by certain ulterior textural changes, tend to produce 

 dilatation or rupture of the fine interconnective tissue of the 

 air-lobules, thus permitting the passage of air into the par- 

 tially destroyed structure. 



The ulterior changes to which we refer are those of impaired 

 nutrition of the pulmonary tissue consequent on arrested cir- 

 culation in the interlobular pulmonary plexuses from disten- 

 sion of the lobes or cells ; this disturbance of nutrition in the 

 intimate texture of the lungs, tending to degenerative changes, 

 will render the tissue more liable to be acted upon injuriously 

 by retamed and imperfectly expired air subject to repeated 

 compression. 



It is from regarding the phenomena of broken-wind, or at 

 least the peculiar dyspnoea characteristic of it, as the imme- 

 diate result of extensive contraction of the smaller bronchi 

 due to tonic spasm of their circular fibres, that the disease has 

 come to be regarded as analogous to asthma in the human 

 subject, to which it certainly bears a close resemblance in 

 many of its features. However, if we regard the term asthma 

 as meaning a condition or assemblage of phenomena depen- 

 dent on spasmodic contraction of the bronchial muscular 

 tissue, we cannot accept this as the true pathology of the con- 



