170 PHYSIOLOGICAL CHEMISTRY. 



mental emotions and by irritation of the glandular nerves, either di- 

 rectly (in animals) or reflexly, by mechanical or chemical irritation 

 of the mucous membrane of the mouth. Among the chemical irri- 

 tants the acids take first place, while alkalies and pungent substances 

 have little action. Sweet-tasting bodies, such as honey, are said to 

 have no effect. Mastication has great influence in the secretion of 

 parotid saliva, which is especially marked in certain herbivora. 



Human parotid saliva may be collected by the introduction of a 

 canula into the parotid duct. This saliva is thin, less alkaline than 

 the submaxillary saliva (the first drops are sometimes neutral or 

 acid), without special odor or taste. It contains a little albumin 

 but no mucin, which is to be expected from the construction of the 

 gland. It also contains a diastatic enzyme, which, however, is ab- 

 sent in many animals. The quantity of solids varies between 5 and 

 16 p. m. The specific gravity is 1.003-1.012. Potassium sulpho- 

 cyanide seems to be present, though it is not a constant constituent. 

 KULZ found 1.46$ oxygen, 3.2$ nitrogen, and in all 66.7$ carbon 

 dioxide in human parotid saliva. The quantity of closely-com- 

 bined carbon dioxide was 62$. 



The mixed buccal saliva in man is a colorless, faintly opales- 

 cent, slightly ropy, easily frothing liquid without special odor or 

 taste. It is made turbid by epithelium cells, mucous and salivary 

 corpuscles, and often by food residues. Like the submaxillary 

 and parotid saliva, on exposure to the air it becomes covered 

 with an incrustation consisting of calcium carbonate and a small 

 quantity of an organic substance, or it gradually becomes cloudy. 

 Its reaction is alkaline, but occasionally also acid. According 

 to STICKER, fresh saliva may be acid a few hours after a meal. 

 Two or three hours after breakfast and four to five hours after 

 dinner the maximum of acidity occurs, and it may also be faintly 

 acid from midnight to morning. The specific gravity varies between 

 1.002 and 1.009, and the quantity of solids between 5 and 10p.m. The 

 solids, irrespective of the form-constituents mentioned, consist of 

 albumin, mucin., ptyalin, and mineral bodies. It is also claimed 

 that urea is a normal constituent of the saliva. The mineral bodies 

 are alkali chlorides, bicarbonates of the alkalies and calcium, phos- 

 phates, and traces of sulphates and sulphocyanides. 



