(52 DISEASES OF THE TRACHEA AND BRONCHI. 



disposition to catarrh, and, when exposed to the action of even trifling 

 irritants, are much more liable to bronchial catarrh than well-nourished 

 persons of firmer fibre. This predisposition depends, probably, upon 

 increased susceptibility, or feebler capacity for withstanding noxious 

 influences ; or it may be attributed to the poor nutritive condition and 

 weak resisting power of the walls of the capillaries, and yielding nature 

 of the tissues through which they run. An augmented tendency to hy- 

 peraemia and to increased transudation would result from such a con- 

 dition. The disposition to catarrh in general, and hence to bronchial 

 catarrh, seen in scrofula and rickets, should also be placed under this 

 heading. Thirdly : those who have often suffered from bronchial ca- 

 tarrh show a proneness to the disease ; chronic disease of the paren- 

 chyma of the lungs augments this inclination, if it does not give rise 

 to the disease itself. The old saying, " Ubi irritatio ibi affluxus" 

 still holds good ; although the afflux is only produced by dilatation of 

 the vessels leading to the point of irritation, or by defective resisting 

 power of the vascular walls, and must not be supposed to be due to 

 attraction. Lastly : the liability to this affection is less among those 

 who inure themselves to exposure. 



The exciting causes of bronchial catarrh, which act more or less 

 readily, according to the tendency of the individual, are as follows : 

 First : it may proceed from an impeded evacuation of the bronchial veins. 

 For the bronchial arteries which spring from the aorta, or intercostal 

 arteries, transmit only a portion of their blood into the bronchial veins, 

 whence it proceeds by the vena azygos into the vena cava. Another 

 portion of the blood of the small bronchial veins flows within the sub- 

 stance of the lung into the pulmonary veins ; hence, both in contrac- 

 tion of the mitral valve, impeding the outflow from the left auricle, 

 and in cases of insufficience of the mitral, with systolic regurgitation 

 from ventricle to auricle, and consequent impeded outflow to the con- 

 tents of the left auricle and pulmonary vein, the immediate effect will 

 be hyperoemia of the lungs (that is, capillary engorgement of the al- 

 veoli) ; and if the cardiac lesion be severe, bronchial catarrh not only 

 is one of the most constant but one of the most physiological and in- 

 evitable symptoms which arise. To understand this condition, we 

 must keep in mind that a part of the blood of the bronchial mucous 

 membrane flows into the left side of the heart instead of the right. 

 The fact that chronic affections of the pulmonary substance are com- 

 plicated with bronchial catarrh is ascribable to the above-mentioned ar- 

 rangement of the vessels ; for if the circulation of the lung-tissue be de- 

 ranged, then the task of the smaller bronchial veins in returning blood 

 to the pulmonary veins will be increased, so that engorgement arises in 

 the corresponding bronchi, which becomes all the more intense if any of 

 the bronchial veins be compressed by inflammatory foci or by growths. 



