62 HISTOLOGY 



pulpy contents of the entire spleen, so as to leave the framework of con- 

 nective and recticular tissue, which may be inflated and dried (Zeitscbr. 

 f. Morph., 1900, vol. 2, pp. 1-42). Such preparations give an idea of 

 the intricacy of the reticular meshwork that can be obtained in no other 

 way, and yet the finer ramifications have been destroyed by this process. 



There has been considerable discussion as to whether the fibers of reticular tissue are 

 chemically different from those of ordinary connective tissue. They differ from the 

 elastic elements of connective tissue, since reticular fibers are dissolved by both acids 

 and alkalis which leave the elastic fibers intact; and they are not destroyed by pancreatic 

 digestion which causes the elastic fibers to disintegrate. But the differentiation of the 

 reticular fibers from the "white fibers" of connective tissue has not been successfully 

 accomplished. Mall has shown, however, that tendon, consisting largely of white fibers, 

 is dissolved more readily by boiling in p.c. solutions of potassium hydrate or hydro- 

 chloric acid, respectively, than sections of lymph glands; and the name reticulin has 

 been introduced for a constituent of the reticular fibers which does not yield gelatin on 

 boiling. Reticulin is not generally recognized as an independent substance, and 

 reticular tissue often appears to blend with white fibrous connective tissue. 

 The recognition of reticular tissue depends, therefore, on its form rather than on 

 its chemical constitution. 



Mucous TISSUE. 



The substance of the umbilical cord is composed of mucous tissue. 

 At birth it is a peculiar gelatinous mass of pearly luster, which has long 

 been known anatomically as Wharton's jelly. During its development 

 from mesenchyma, a large amount of mucus becomes deposited in its 

 intercellular spaces. This mucus, like that produced in the goblet cells 

 and that found in the cornea and vitreous body of the eye, is a trans- 

 lucent substance which contains mucin. Chemically there are many 

 (varieties of mucins. They are compound protein bodies containing a 

 'carbohydrate complex in their molecules, and are therefore known as 

 glycoproteins. True mucins are formed in abundance in goblet cells and 

 in mucous tissue; to a less extent they occur in all embryonic connective 

 tissue. Related substances, called mucoids, have been obtained from 

 tendon, cartilage and bone. 



In the umbilical cord the mucus may be regarded as a secretion which 

 is produced without the formation of special granules or vacuoles, and is 

 discharged equally from all surfaces of the cells. It is a homogeneous 

 ground-substance, in which extremely delicate fibrils are imbedded. These 

 are gathered in wavy bundles (Fig. 51, a). Fibrils of the same sort, 

 generally arranged in denser bundles, are found in ordinary connective 

 tissue, and constitute the white fibers. Chemically they are said to con- 

 sist of collagen, an albuminoid body which on boiling yields gelatin, the 

 source of glue. The origin of the collagenous fibers has been the subject 

 of repeated investigation. Henle (1841) considered that they arose in 



