136 THE ESSENTIALS OF HISTOLOGY 



LESSON XXVII. 



THE SALIVARY GLANDS. 



1. STUDY carefully sections of the subniaxillary gland of a dog. The 

 gland should have been hardened in alcohol and stained with logwood. 

 Notice the acini filled with clear cells, the nuclei of which usually lie near the 

 basement-membrane. Notice here and there, outside the clear cells, demi- 

 lunes or crescents of small darkly stained granular-looking cells. Observe also 

 the sections of the ducts with their striated columnar epithelium. Try and 

 find a place where one of the ducts is passing into the alveoli. Sketch under 

 a high power. 



2. Study sections of the parotid gland prepared in a similar way. 



3. Examine small pieces of both subrnaxillary and parotid gland fresh in 

 saline solution. In' the submaxillary gland notice that the alveolar cells are 

 swollen out with clear niucigen, but that those of the parotid are filled with 

 granules (zyrnogen). 1 Make a sketch from each preparation under a high 

 power. 



4. Prepare a transverse section of the oesophagus. Notice the thick 

 muscular coat partly containing cross-striated fibres and the mucous mem- 

 brane with its papillae and stratified epithelium. Look for mucous glands in 

 the areolar coat. Sketch under a low power. 



The salivary glands may be looked upon as typical of secreting 

 glands in general. They are composed of a number of lobules bound 

 together loosely by connective tissue. Each small lobule is formed of 

 a group of saccular or somewhat tubular alveoli or acini (fig. 166) from 

 which a duct passes, and this, after uniting with other ducts to form 

 larger and larger tubes, eventually leaves the gland to open upon the 

 surface of the mucous membrane of the mouth. 



The alveoli are enclosed by a basement-membrane, which is 

 reticular (fig. 167). This basement-membrane is continued along the 

 ducts. Within it is the epithelium, which in the alveoli is composed of 

 polyhedral cells (fig. 168, a), but in the ducts is regularly columnar, 

 except in that part of the duct which immediately opens into the 



1 To study the changes which the alveolar cells undergo during secretion, pilo- 

 carpine is injected subcutaneously into an animal in sufficient amount to produce 

 copious salivation ; after which the animal is killed and its salivary glands are 

 examined as in preparation 3. The granules are not seen in preparations that 

 have been in alcohol, but osmic acid preserves them ; they are best seen, however, 

 in the fresh tissue. 



