ORAL DIGESTION. 565 



the secretion of which is augmented, not only by the presence of food, 

 but even by the sight of it, especially if the food be desirable; giving 

 rise to what is called "mouth-watering." It is probable, that, inde- 

 pendently of mental association, the action of the secretory organs is 

 increased by the agitation of the organs themselves during the masti- 

 catory movements. It has, indeed, been asserted, that the parotid 

 glands are so situate, as regards the jaws, that the movement of the 

 lower jaw presses upon them, and forces out the saliva ; but MM. 

 Bordeu and J. Cloquet have demonstrated, anatomically and by ex- 

 periment, that this is not the case. 1 



It has been supposed by some, that admixture with saliva communi- 

 cates to the food its first degree of animalization ; or in other words, its 

 first approximation to the substance of the animal it has to nourish. 

 Such are the opinions of Professor S. Jackson 2 and M. Yoisin. 3 The 

 former asserts, that he has ascertained positively, that the saliva exerts 

 a very energetic operation on the food, separating, by its solvent pro- 

 perties, some of its constituent principles, and performing a species of 

 digestion. MM. Tiedemann and Gmelin, too, think that the water, and 

 the carbonates and acetates of potassa and soda, and the chlorides of 

 potassium and sodium, of the saliva, contribute to soften and dissolve 

 the food ; whilst the nitrogenized materials, the salivary and albuminous 

 matters, communicate to it a first degree of animalization. It is more 

 probable, however, that the great use of mastication and insalivation is 

 to give the food the necessary consistence, in order that the stomach 

 and small intestine may exert their action upon it in the most favourable 

 manner; and that, consequently, the changes effected upon it in the 

 mouth, are chiefly of a mechanical character. In the case of many 

 substances as sugar, salt, &c. a true solution takes place in the 

 saliva; and this probably happens to sapid bodies in general; the par- 

 ticles being separated by imbibing the fluid. Krimer, 4 of Leipzig, held 

 in his mouth a piece of ham, weighing a drachm, for three hours. At 

 the expiration of this time, the ham was white on its surface, and had 

 increased in weight twelve grains. Krimer, it may be remarked, be- 

 lieves, that the tears assist in digestion, and that they flow constantly 

 by the posterior nares into the stomach. It would seem, too, that an 

 important action of the saliva is the conversion of starch into dextrin 

 or grape sugar. From one drachm of starch, Dr. Wright 5 obtained in 

 twelve hours, at a temperature of 98, by admixture with saliva, thirty- 

 one grains of sugar. This probably takes place by the action of some 

 nitrogenized secretion, like pepsin in stomachal digestion. It has been 

 affirmed, indeed, on the strength of numerous and varied experiments 

 detailed before the French Academy of Sciences, 6 by MM. Bernard de 

 Yillefranche and Barreswil, that in the gastric juice, pancreatic fluid, 

 and saliva, an organic principle exists, which is common to them all; 

 and that it is the nature of the chemical reaction associated with it, 

 which alone determines their power of digesting the different aliment- 



* Adelon, op. cit., ii. 418. 2 p r i nc i p ies of Medicine, p. 354, Philad., 1832. 



3 Nouvel Aper^u sur la Physiologie du Foie, &c., Paris, 1833. 



4 Versuch einer Physiologie des Blutes, Leipz., 1820. 



* Lond. Lancet, 1841-2. 6 Comptes Rendus, 7 Juiilet, 1845. 



