Note (47) — CANTO FIFTH.

“Mechanical trituration is not the only change that the food undergoes in the mouth. Subjected to the action of the organs of mastication, which overcome the force of cohesion of its molecules, it is at the same period imbued with saliva. This fluid, secreted by glands placed in the vicinity of the mouth, is poured in considerable quantity into that cavity during mastication.

“The saliva is a transparent and viscous fluid, formed of about four parts of water and one of albumen, in which are dissolved phosphate of lime, of soda, and of ammonia, as well as a quantity of muriate of soda. Like all other albuminous fluids, it froths when agitated, by absorbing oxygen, for which it appears to have a strong affinity. Its affinity for oxygen is such, that we may oxydize gold and silver by triturating in saliva, thin leaves of these metals, which are of such difficult oxydizement. The irritation occasioned by the presence or desire of food, and by mastication, excites the salivary glands, which swell and become so many centres of fluxion, towards which the humours flow abundantly.

“It is estimated that about six ounces of saliva are secreted during the average time of a meal. It flows in greater quantity when the food is acrid and stimulating. It mixes with the mucus copiously secreted from the glands, and with the serous fluids exhaled by the exhalent arteries of the mouth. There can be no doubt that the saliva, mixing with the food by the motion of the jaws, absorbs oxygen, and unites to the alimentary substances a quantity of that gas fit to bring about the changes they are ultimately destined to undergo.” (Richerand’s Physiology, p. 96.)