THE SALIVARY GLANDS. 161 



LESSON XXIX. 



THE SALIVARY GLANDS. 



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

 may be hardened in alcohol and stained with luematoxylin. Notice the acini 

 filled with clear cells, the nuclei of which usually lie near the basement-mem- 

 brane. Notice here and there, outside the clear cells, demilunes 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 submaxillary and parotid gland of the dog 

 fresh in 2 per cent, salt solution. In the submaxillary gland notice that the 

 alveolar-cells are swollen out with large granules or droplets of mucigen, 

 which swell up in water to form large clear vacuoles. Dilute acids and 

 alkalies produce a similar change. The cells of the parotid gland are also 

 filled with granules (zymogen), but they are smaller, and simply dissolve in 

 watery fluids. 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 papilla? 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. 189) 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 inclosed by a basement-membrane, which is 

 reticular (fig. 190). This basement-membrane is continued along the 

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

 polyhedral cells (fig. 191, a), but in the ducts is regularly columnar, 



1 To study the changes which the alveolar cells undergo during secretion, pilocarpine is 

 injected subcutaneously into an animal in sufficient amount to produce copious saliva- 

 tion ; after which the animal is killed and its salivary glands are examined as in prepara- 

 tion 3. The granules are not seen in preparations that have been in alcohol, but osmic 

 acid preserves them ; they are best seen in the fresh tissue. 



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