18 HANDBOOK OF PHYSIOLOGY. 



which may persist as a hyaline saccule after the gland-cells have all 

 been discharged. 



(2) By anastomosis of their processes. This is the usual way in which 

 stellate cells, e. g., of the cornea, are united ; the individuality of each 

 cell is thus to a great extent lost by its connection with its neighbors to 

 form a reticulum ; as an example of a network so produced we may cite 

 the stroma of lymphatic glands. 



Sometimes the branched processes breaking up into a maze of minute 

 fibrils, adjoining cells are connected by an intermediate reticulum ; this 

 is the case in the nerve-cells of the spinal cord. 



Derived tissue-elements. Besides the Cell, which may be termed the 

 primary tissue-element, there are materials which' may be termed secon- 

 dary or derived tissue-elements. Such are Intercellular substance, 

 Fibres, and Tubules. 



a. Intercellular substance is probably in all cases directly derived 

 from the cells themselves. In some cases (e. g., cartilage), by the use 

 of reagents the cementing intercellular substance is, as it were, analyzed 

 into various masses, each arranged in concentric layers around a cell or 

 group of cells, from which it was probably derived (Fig. 46). 



ft. Fibres. In the case of the crystalline lens, and of muscle both 

 striated and non-striated, each fibre is simply a metamorphosed cell: in 

 the case of the striped fibre the elongation being accompanied by a mul- 

 tiplication of the nuclei. 



The various fibres and fibrillae of connective tissue result from a grad- 

 ual transformation of an originally homogeneous intercellular substance. 

 Fibres thus formed may undergo great chemical as well as physical 

 transformation: this is notably the case with yellow elastic tissue, in 

 which the sharply defined elastic fibres, possessing great power of resis- 

 tance to reagents, contrast strikingly with the homogeneous matter from 

 which they are derived. 



y. Tubules, such as the capillary blood-vessels, which were originally 

 supposed to consist of a structureless membrane, have now been proved 

 to be composed of flat, thin cells, cohering along their edges. 



"With these simple materials the various parts of the body are built 

 up; the more elementary tissues being, so to speak, first compounded of 

 them; while these tissues are variously mixed and interwoven to form 

 more intricate combinations. 



Thus are constructed epithelium and its modifications, the connec- 

 tive tissues, the fibres of muscle and nerve, etc. ; and these, again, with 

 the more simple structures before mentioned, are used as materials 

 wherewith to form arteries, veins, and lymphatics, secreting and vascu- 

 lar glands, lungs, heart, liver, and other parts of the body. 



In this chapter the leading characters and chief modifications of the 



