BRONCHITIS. 



615 



in fact before any external signs of disease were manifested. 

 He says — " On careful comparison, however, of many cases, w^e 

 feel assured that the first deviation visible is a relaxation and 

 distension of the abundant plexus of blood-vessels ramifying in the 

 inner fibrous coat, immediately beneath the basement membrane 

 — that is to say, of the branches of the bronchial artery. They 

 become engorged with blood, so that on transverse section they 

 appear like little cavities distended with blood corpuscles. In a 

 few hours afterwards the basement membrane ^ becomes much 

 more apparent than it usually is, and at the same time more 

 clear and homogeneous, while the surface is thrown into many 

 folds. These changes in the basement membrane are appa- 

 rently clue to its becoming oedematous, serous fluid being infil- 

 trated into it from the underlying plexus of distended vessels ; 

 and we shall see that, as the acute irritation continues, this 

 oedematous state of the basement membrane becomes more and 

 more a well-marked feature. The next change, so far as we 

 have been able to calculate, occurs in from twenty to thirty 



Fig. 40. — Bronchus (medium sized) in acute bronchitis. — (American ox 

 slaughtered at Liverpool. ) 

 (a) Deep layer of epithelium, germinating and throwin off catarrhal cells. 

 (6) Inner fibrous coat, infiltrated with inflammatory cells. (480 diam.) 

 The cokimnar epithehum shed. 



1 The basement membrane is not so apparent in the lower animals as 

 in man. 



