THE SUPPORTING TISSUES 



37 



60. The epithelial structures may be placed according 

 to their functions, in two divisions. One is chiefly protec- 

 tive in character ; such as the outer skin, the lining of the 

 mouth and windpipe, the epithelial layers protecting the 

 delicate nerves and blood vessels beneath. The other kind 

 of epithelial tis- 

 sue consists of 



cells that con- 

 tain highly 

 active proto- 

 plasm and are 

 actively en- 

 gaged in form- 

 ing fluids called 

 secretions, from 

 food brought 

 to them by the 

 blood (Figs, ii 

 to 17). Such 

 are the cells of 

 the salivary 

 glands, which 

 secrete the 

 saliva (Fig. 

 40); of the 

 gastric glands, 

 which secrete 

 gastric juice 



(Fig. 41 ); of the pancreas, sweat glands, kidneys, liver, 

 etc. This class of epithelial tissue is, therefore, of the 

 greatest value in purifying the body and in preparing 

 material to be used in its activities: it is essential to the 

 growth of sound and well-nourished nerve and muscle. 



61. Cartilaginous Tissue. Some parts of the body 

 require tissue having something of the rigidity of bones, 



FIG. 38. Fatty Tissue. 



ve ^ at ce ^ s > ^ e ^ together by bundles of connective tissue f\ m, 

 t he membrane or envelope of the fat cell ; n, the nucleus, and p, 

 remains of the protoplasm pushed aside by large oil drop a. 

 Magnified 200 diameters. 



