RETICULAR AND OTHER CONNECTIVE TISSUES 283 



In the smaller arteries and in the small and medium veins the coat 

 of Henle is so thin, and often incomplete, that it is more difficult 

 to determine that the elastic fibers are colorless as distinguished 

 from the blackened reticulum but in view of the constant and 

 obvious condition in the larger vessels one is warranted in assum- 

 ing that the elastic fibers in the smaller vessels, as in the larger, 

 are colorless and that it is the reticulum, when present, which 

 blackens. The intimate clothing of elastic fibers by reticulum, 

 readily observed in the larger vessels, accounts for the occasional 

 appearance of blackened fibers in the position of Henle's coat in 

 vessels so small as to possess only an incomplete internal elastic 

 membrane. 



In the basement membranes of the bronchii one finds only 

 argentiferous reticular fibers. In the larger bronchi the basement 

 membrane is specially distinct and consists of a dense, closely 

 packed mesh of blackened reticular fibers (fig. 3), forming a com- 

 plete membranous investment continuous with the reticular fibers 

 of the tunica propria and supporting the epithehum. With the 

 Weigert-elastic picro-fuchsin stain the argentiferous fibers take 

 a red color. 



In the tunica propria of the trachea and bronchi are large bun- 

 dles of longitudinal elastic fibers. These fibers remain colorless 

 in the Bielschowsky sections even when the stain has been made 

 so intense as to darken to a considerable extent the collaginous 

 fibers and the muscles. One finds each elastic fiber invested by a 

 distinct coat of blackened reticular fibers forming an intricate 

 net. If one selects a known and readily recognized point for 

 study, consecutive sections stained by different methods show 

 the broad lines of elastic fibers, which in the Bielschowsky sec- 

 tions are colorless, to be flanked on every surface by a blackened 

 reticulum, but clothed in the Weigert-elastic picro-fuchsin section 

 by fuchsin stained fibers. With haematoxylin and eosin the whole 

 breadth of the basement membrane and both elastic and argentif- 

 erous fibers in the tunica propria take the characteristic eosin 

 tint, and reticular and elastic fibrils are almost indistinguishable. 



Thus wherever the recognition of unquestionable elastic fibers 

 can be made with certainty they are found uncolored by the silver, 



