174 PHYSIOLOGICAL CHEMISTRY. 



tion is slower and less abundant (HEIDENHAIN). The amount of 

 salts increases also to a certain degree by an increasing rapidity of 

 elimination (HEIDENHAIN, WERTHER, LANGLEY and FLETCHER, 

 NOVY). 



The chemical changes taking place during secretion are un- 

 known, but it is probable that, like the secretion processes in gen- 

 eral, the secretion of saliva is closely connected with the processes 

 in the cells. HEIDEKHAIN claims that the mucin-cells of the sub- 

 maxillary gland are destroyed (while EWALD and STOHR claim that 

 they only lose mucin), and in the period of rest the mucin reap- 

 pears in these cells. These observations still do not throw any light 

 upon the chemical processes going on. 



The Physiological Importance of the Saliva. The quantity of 

 water in the saliva renders possible the effects of certain bodies on 

 the organs of taste, and it also serves as a solvent for a part of the 

 nutritive substances. The importance of the saliva in mastication 

 is especially marked in herbivora, and there is no question of its 

 importance in facilitating the act of swallowing. The power of 

 converting starch into sugar does not belong to the saliva of all 

 animals, and even when it possesses this property the intensity 

 varies in different animals. In man, whose saliva forms sugar ra- 

 pidly, a formation of sugar from (boiled) starch undoubtedly takes 

 place in the mouth, but how far this action goes on after the morsel 

 has entered the stomach depends upon the rapidity with which the 

 acid gastric juice mixes with the swallowed food, and also upon the 

 relative amounts of the gastric juice and food in the stomach. The 

 large quantity of water which is swallowed with the saliva must 

 be absorbed and pass into the blood, and it must go through an 

 intermediate circulation in the organism. Thus the organism pos- 

 sesses in the saliva an active medium by which a constant stream, 

 conveying the dissolved and finely-divided bodies, passes into the 

 blood from the intestinal canal during digestion. 



Salivari Calculi. The so-called tartar is yellow, gray, yellowish gray, 

 brown or black, and has a stratified structure. It may contain more than 200 

 p. m. organic substances, which consist of mucin, epithelium, and LEPTO- 

 THKIX. The chief part of the inorganic constituents consists of calcium car- 

 bonate and phosphate. The salivary stone may vary in size from the size of 

 a small grain to that of a pea or still larger (a salivary stone has been found 

 weighing 18.6 grms.), and it contains a variable quantity of organic substances, 

 50-380 p. m., which remain on extracting the stone with hydrochloric acid. 

 The chief inorganic constituent is calcium phosphate. 



