RETICULAR AND OTHER CONNECTIVE TISSUES 287 



whereas the reticukim in the walls of the alveoli and smaller bron- 

 chi, though often composed of coarse typically spiral fibrils, forms 

 an interlacing mass of discreet fibers, or fiber bundles, among 

 which a limited proportion of finer bundles of brownish collag- 

 inous fibers may be recognized. In the vascular trabecula of the 

 spleen (fig. 7) the collaginous fibers of the blood-vessels acquire 

 a typical brown while the close network of reticular fibers take on 

 an intense black and have a characteristic, either somewhat 

 regularly spiral, or a reticular course, very different from the 

 irregularly wavy collaginous fibers. 



Fig. 7 A vascular trabeculum of a child's spleen. The blackened fiber.s of 

 reticulum (r) show clearly in contrast to the collaginous fibers (c/) which in the sec- 

 tion are a golden brown. The reticulum surrounds the vessels and is continuous 

 with that of the splenic pulp. Bielschowsky stain. Drawn with Edinger pro- 

 jection apparatus, X 255. 



In the trabecula of the Ijanphatic glands the distribution is not 

 so apparent, the collaginous and the reticular fibers pursuing some- 

 what similar courses, though the latter are apt to be more dis- 

 tinctly spirillar. From careful examination I am led to believe 

 that the relation simulates, in reverse, that already described (see 

 fig. 2) for the elastic fibers, in that it would appear with consider- 

 able certaint}^ in many places that the black reticular fibers are 

 invested or enveloped by a sleeve or coat of collaginous fibrils, 

 so that the latter fibrils consequently assume a spiral course cor- 

 responding closely to that of the reticular fibrils. Indications of 

 a similar investment of the reticular fibrils can be found wherever 

 reticulum occurs, but it is not always possible to distinguish 

 with certainty between the collaginous fibers and the protoplasm 

 of mesenchymal or fixed connective tissue cells. 



