286 J. S. FERGUSON 



('07), Cesa-Biaiichi ('()8), Bahihio ('08), Alagno ('08). The retic- 

 ular fibers assume a dense opacjiie black while the collaginous 

 fibers take on a golden i)rown when well differentiated. Yet 

 if one examines carefully those points at which the two tissues 

 blend one encounters much difficulty in determining whether the 

 black color of the coarser collaginous bundles is due to the opacity 

 of the brown l)undles — which are of considerable size and thick- 

 ness and often of great density — or to the presence within the 

 coarse collaginous bundles of finer, blackened, reticular fibers. 

 In some locations the latter relation is apparent. For example, 

 in the perifollicular plexus about the lymphatic follicles, described 

 by Ciaccio ('07), one finds the characteristic lozenge shaped 

 meshes of the 'reticulum' extending into the adjacent collaginous 

 tissue of the trabecula in lymphoid organs or of the tunica pro- 

 pria and submucosa in the digestive tract, but there the reticular 

 fibers are nearly always clear and sharp among the collaginous 

 fibers of the smaller fibrous bundles (figs. 5, 6, 7, and 13). As the 

 bundles increase in size, however, the difficulty of distinguishing 

 the exact outlines of the two types of fibers increases. 



Another difficulty in the way of exact and positive differentia- 

 tion is the variable result of silver impregnations. With vary- 

 ing degrees of impregnation, reduction, and toning the collaginous 

 fillers may lose their typical golden brown and accjuire an increas- 

 ingly opaque condition. This is specially prone to occur if the 

 sections are overtoned in the gold chloric! bath. One halts, there- 

 fore, between the idea of similarity if not positive identity of col- 

 laginous fibers and "reticulum" and the opinion of Mall ('01) 

 which regards reticulum as an independent tissue, distinctly dif- 

 ferentiated from the collaginous by its somewhat different chem- 

 ical reactions, a view not fully accepted by Studnicka ('03) nor 

 yet generally adopted by German authors (Fiirbringer, '09). Yet 

 if one uses care with the silver process one can obtain from nearly 

 all tissues (luite distinctive preparations. Thus in the lung the 

 fibrous tissue of the pleura, as shown by Favaro ('09), as well 

 as that of the "interlobular septa" appears to be formed by golden 

 brown fibers arranged in bundles having the characteristic wavy 

 course together with but few intermingled black reticular fibers, 



