CHAPTER XXXII 



SALIVA 



THE saliva is formed by three pairs of salivary glands, called the 

 parotid, submaxillary, and sublingual glands. 



The Salivary Glands. 



These typical secreting glands are made up of lobules united 

 by connective tissue. Each lobule is made of a group of tubulo- 

 saccular alveoli or acini, from which a duct passes ; this unites with 



other ducts to form larger and larger 

 tubes, the main duct opening into the 

 mouth. 



Each alveolus is surrounded by a 

 plexus of capillaries ; the lymph which 

 exudes from these is in direct contact 

 with the basement membrane that en- 

 closes the alveolus. The basement mem- 

 brane is lined by secreting cells which 

 surround the central cavity or lumen. 

 The basement membrane is thin in 

 many places, to allow the lymph more 

 ready access to the secreting cells; it 

 is continued along the ducts. 



The secreting cells differ according 

 to the substance they secrete. In alveoli 

 that secrete mucin (such as those in the sublingual gland and some 

 of the alveoli in the submaxillary) the cells after treatment with 

 water or dilute acid are clear and swollen (fig. 350) ; this is the 

 appearance they usually present in sections of the organ. But if 

 examined in their natural state by teasing a portion of the fresh gland 

 in serum, they are seen to be occupied by large granules composed 

 of a substance known as mucigen or mucinogen (fig. 349). When the 

 gland is active, mucigen is transformed into mucin and discharged as 



FIG. 318. From a section through a 

 salivary gland, a, Serous or albumi- 

 nous alveoli ; b, intralobular duct 

 cut transversely. (Klein and Noble 

 Smith.) 



