SALIVA 45 



The submaxillary and sublingual glands are called mucous 

 glands ; their secretion contains mucin. Mucin is absent from 

 parotid saliva. The granules in the cells are larger than those of 

 the parotid gland ; they are composed of mucinogen, the precursor 

 of mucin (see fig. 13). 



In a section of a mucous gland prepared in the ordinary way the 

 mucinogen granules are swollen out, and give a highly refracting 

 appearance to the mucous acini (see fig. 14). 



COMPOSITION OF SALIVA 



On microscopic examination of mixed sahva a few epithelial 

 scales from the mouth and salivary corpuscles from the salivary 

 glands are seen. The Mquid is transparent, slightly opalescent, of 

 slimy consistency, and may contain lumps of nearly pure mucin. 

 On standing it becomes cloudy owing to the precipitation of calcium 

 carbonate, the carbonic acid which held it in solution as bicarbonate 

 escaping. 



Of the three forms of saliva which contribute to the mixture 

 found in the mouth, the sublingual is richest in solids (2'75 per cent.). 

 The submaxillary saliva comes next (2"1 to 2-5 per cent.). When 

 artificially obtained by stimulation of nei"ves in the dog the saliva 

 obtained by stimulation of the sympathetic is richer in solids than 

 that obtained by stimulation of the chorda tympani. The pai'otid 

 sahva is poorest in total solids (03 to 0*5 per cent.), and contains no 

 mucin. Mixed saliva contains in man an average of about 0-5 per 

 cent, of solids : it is alkaline in reaction, due to the salts in it ; and 

 has a specific gravity of 1002 to 1006. 



The solid constituents dissolved in saliva may be classified 

 thus : — 



/ a. Mucin : this may be precipitated by acetic acid. 



- . '6. Ptyahn : an amylolytic ferment. 

 Orfiramc -( . ^ ^ 



] c. Proteid : of the nature of a globulin. 



d. Potassium sulphocyanide. 



e. Sodium chloride : the most abundant salt. 



- • j /• Other salts : sodium carbonate, calcium phosphate 



1 and carbonate ; magnesium phosphate ; potassium 

 I chloride. 



THE ACTION OF SALIVA 



The action of sahva is twofold, physical and chemical. 

 The physical use of sahva consists in moistening the mucous 

 membrane of the mouth, assisting the solution of soluble substances 



