THE TISSUES 25 



is collected at their point of attachment, while the body of 

 the cell is filled with mucin, a clear, transparent material. 



3. Glandular Epithelium. A number of cells, having for 

 their function the production of some material which is to be 

 excreted from the cell, are arranged as the lining of depres- 

 sions, the glands. 



The simplest form of gland is the simple tubular a test- 

 tube-like depression, lined by secreting cells. Instead of 

 being simple, the tube may be branched, when the gland is 

 said to be racemose. In many glands the secreting epi- 

 thelium is confined to the deeper part of the tube, the 

 alveolus or acinus (Fig. 6), while the more superficial part 

 is lined by cells which do not secrete, forming the duct. 



In many situations several simple glands are grouped 

 together, their ducts opening into one common duct, and 

 a compound gland results. 



Secreting epithelium varies according to the material it 

 produces. 



(A) Mucin-secreting Epithelium. Many glands have for 

 their function the production of mucin, a slimy substance 

 of use in lubricating the mouth, stomach, intestine, &c. 

 The acini containing such cells are usually large. The cells 

 themselves are large, and are placed on a delicate basement 

 membrane, a condensation of the subjacent fibrous tissue, 

 which bounds the acinus. The nuclei are situated near 

 to the attached margin of the cells, which are somewhat 

 irregular in shape, and are packed close together. Their 

 appearance varies according to whether the gland has been 

 at rest or has been actively secreting. 



Resting State. In the former case, in the fresh condi- 

 tion, the cells are large, and pressed closely together. Their 

 protoplasm is filled with large shining granules. After treat- 

 ment with reagents, each cell becomes distended with clear, 

 transparent mucin, formed by the swelling and coalescence 

 of the granules. 



After Activity. After the gland has been actively secret- 

 ing, the cells are smaller and the granules are much less 

 numerous, being chiefly situated at the free extremity of the 

 cell, and leaving the nucleus much more apparent. 



This form of epithelium, during the resting condition of 



