SEC. 1. THE CHARACTERS AND PROPERTIES OF 

 SALIVA AND GASTRIC JUICE. 



Saliva, 



175. 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 

 corpuscles. Its reaction in a healthy subject is alkaline, espe- 

 cially 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 T002 to 1 - 006. Of these solids, rather less than half, about 

 2 p.c., are salts (including at times a minute quantity of potas- 

 sium 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 con- 

 stituent, 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 

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

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

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

 stirred while the acid is being added, the mucin is apt to be pre- 

 cipitated 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 an other salts ; 

 thus after the addition of sodium chloride acetic acid even in con- 

 siderable excess will not cause a precipitate of mucin. 



