SEC. 1. THE CHARACTERS AND PROPERTIES OF 

 SALIVA AND GASTRIC JUICE. 



Saliva. 



197. Mixed saliva, as it appears in the mouth, is a thick, 

 glairy, generally frothy and turbid fluid. Under the microscope it 

 is seen to contain, besides the molecular debris of food, bacteria and 

 other organisms (frequently cryptogamic spores), epithelium-scales, 

 mucus-corpuscles and granules, and the so-called salivary cor- 

 puscles. Its reaction in a healthy subject is alkaline, especially 

 when the secretion is abundant. When the saliva is scanty, or 

 when the subject suffers from dyspepsia, the reaction of the mouth 

 may be acid. Saliva contains but little solid matter, on an average 

 probably about '5 p. c., the specific gravity varying from 1*002 to 

 T006. Of these solids, rather less than half, about '2 p.c., are salts 

 (including at times a minute quantity of potassium sulphocyanate). 

 The organic bodies which can be recognised in it are globulin and 

 serum-albumin (see 16, 17) found in small quantities only, other 

 obscure bodies occurring in minute quantity, and mucin ,- the 

 latter is by far the most conspicuous organic constituent, the 

 glairiness or ropiness of mixed and other kinds of saliva being due 

 to its presence. 



Mucin. If acetic acid be cautiously added to mixed saliva 

 the viscidity of the saliva is increased, and on further addition of 

 the acid a semi-opaque ropy mass separates out, leaving the rest of 

 the saliva limpid. This ropy mass, which is mucin, if stirred care- 

 fully with a glass rod, shrinks, becoming opaque, clings to the 

 glass rod and may be thus removed from the fluid. If the quantity 

 of mucin be small and the saliva be violently shaken or stirred 

 while the acid is being added, the mucin is apt to be precipitated 

 in flakes, and may then be separated by filtration. It may be 

 added that the precipitation of mucin by acid is greatly influenced 

 by the presence of sodium chloride and other salts ; thus after the 

 addition of sodium chloride acetic acid even in considerable excess 

 will not cause a precipitate of mucin. 



