PROPERTIES OF THE SALIVARY SECRETION. 147 



cording to the analyses of Schmidt, consist chiefly of potassium and sodium 

 chloride, sodium phosphate (to which the alkaline reaction of the saliva ap- 

 pears to be due), calcic carbonate giving it its cloudy appearance when its 

 reaction is neutral (Oehl) earthy phosphates, and oxide of iron. Bernard 

 has shown that various salts, after their introduction directly or indirectly 

 into the Blood, rapidly make their appearance in the saliva; this is particu- 

 larly the case with Iodide of Potassium, which can often, though not always 

 (Harley), be detected in the saliva long before its appearance in the urine. 

 The Tartar which collects upon the teeth, and the salivary concretions which 

 occasionally obstruct the ducts, consist chiefly of the earthy phosphates held 

 together by about 20 per cent, of animal matter. The fluids which are se- 

 creted by the three principal glands appear (from the experiments to be pres- 

 ently cited) to have very different degrees of efficacy, in producing that 

 chemical change in the food which it is the peculiar attribute of this secre- 

 tion to exert. 



103. Of the quantity of Saliva which is secreted daily, it is impossible to 

 form an exact estimate, since it varies greatly with the character of the food 

 ingested, and the frequency with which that food is taken ; the secreting pro- 

 cess being, indeed, almost suspended when the masticating muscles and tongue 

 are completely at rest, unless excited by a nervous stimulus. The taste, the 

 sight, or even the idea, of savory food, is sufficient to cause a flow of saliva, 

 especially after a long fast; but it is by the masticatory movements that this 

 flow is chiefly promoted, so that the amount poured forth will in a great 

 degree depend upon the duration of these movements, this, again, being 

 governed by the degree in which the food requires mechanical reduction. 

 Harley, with great probability, estimates it at from 1 to 2 Ibs. in man. 

 Oehl found the quantity obtained by catheterization from the submaxillary 

 gland, as compared with the parotid, to be as 3 : 1. He obtained only 26 

 grains per hour from a fasting man, and still less (15 grains) after food had 

 been taken. The influence of the kind of food upon the quantity secreted 

 was well shown by Lassaigne, 1 who found on abstracting the Bolus of food, 

 as it passed down the oesophagus in Horses, that 100 parts of green stalks 

 were mingled with 49 parts of saliva, the same quantity of oats and barley 

 with from 113 to 186 parts, and of dry hay with 406 parts of saliva. Dr. 

 Dalton, however, did not observe such difference in Man, 2 since 10 parts of 

 fresh cooked meat gained 48 per cent., whilst dry wheaten bread did not 

 gain more than 55 per cent, of its weight after thorough mastication. In 

 M. Oehl's experiments, Salt, Pepper, Vinegar, and Quinine excited the flow 

 of saliva from the parotid and submaxillary glands to about an equal degree. 

 Honey chiefly effected an increase of the submaxillary saliva. Butler Stoney 3 

 found in a woman with parotid fistula, that the flow of saliva from this gland 

 was stimulated by mastication alone, but much more by the mastication of 

 any sapid substance, especially if acid (tartaric acid). Potassium iodide in- 

 gested by the mouth, appeared in the saliva in 29 min. 30 sec. 



104. Besides the preparation of the food for the ulterior changes which it 

 has to undergo, by promoting its mechanical reduction in the act of mastica- 

 tion, and by facilitating the subsequent admixture of other watery fluids, and 

 besides the material assistance which it affords to the act of deglutition, the 

 Saliva fulfils other and perhaps still more important purposes. Without its 

 solvent action on many of the solid constituents of our food, their taste would 

 be either greatly diminished in intensity or altogether lost. Moreover, by 

 lubricating the surfaces of the mouth and teeth, it prevents the adhesion of 



* 



1 C. llcnd., xxi. p. 362. 2 Human Physiology, 1861, p. 112. 



3 Humphry and Turner's Journ. of Anat. and Phys., 1873, vol. vii, p. 161. 



