PHYSIOLOGICAL IMPORTANCE OF THE SALIVA. 435 



namely, 14.2 grams in the horse and 8 grams in oxen. The quantity of 

 secretion per hour may be 8 to 14 times greater than the entire mass of 

 glands, and there is probably no gland in the entire body, so far as is 

 known at present the kidneys not excepted whose ability of secre- 

 tion under physiological conditions equals that of the salivary glands. 

 A remarkably abundant secretion of saliva is induced by pilocarpine, 

 while atropine, on the contrary, inhibits it. 



That the secretion of saliva, even if we do not consider such substances 

 as ptyalin, mucin, and the like, is not a process of filtration, follows 

 for many reasons, especially the following: The salivary glands have 

 a specific property of eliminating certain substances, such as potassium 

 salts (SALKOWSKI *), iodine, and bromine compounds, but not others, 

 for example, iron compounds and dextrose. It is also noticeable that 

 the saliva is richer in solids when it is eliminated quickly by gradually 

 increased stimulation, and in larger quantities than when the secretion 

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

 also to a certain degree by an increasing rapidity of elimination (HEIDEN- 

 HAIX, WERTHER, LAXGLEY and FLETCHER, Novi 2 ). 



Like the secretion processes in general, the secretion of saliva is closely 

 connected with the processes in the cells. The chemical processes going 

 on in these cells during secretion are still unknown. 



The Physiological Importance of the Saliva. The quantity of water 

 in the saliva renders possible the action 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 as to its importance in facilitating the 

 act of swallowing. The saliva containing mucin is especially important 

 in this regard, and PAWLOW'S school has shown that the secretion 

 also regulates itself in this regard. The saliva is also of importance, as it 

 serves in washing out the mouth and thereby acts as a protection against 

 destructive substances or bodies foreign to the mouth. The power of con- 

 verting starch into sugar is not inherent in the saliva of all animals, and 

 even when it possesses this property the intensity varies in different ani- 

 mals. In man, whose saliva forms sugar rapidly, a production of sugar from 

 (boiled) starch undoubtedly takes place in the mouth, but how far this 

 action proceeds 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 



1 Virchow's Arch., 53. 



2 Heidenhain, Pfliiger's Arch., 17; Werther, ibid., 38; Langley and Fletcher, 

 Proc. Roy. Soc., 45, and especially Phil. Trans. Roy. Soc. London, 180; Novi, Arch, 

 f. (Anat. u.) Physiol., 1888. 



