HANDBOOK OF PHYSIOLOGY. 



d. Upon pure oleaginous principles the gastric juice has no action. In 

 the case of adipose tissue, its effect is to dissolve the areolar tissue, albu- 

 minous cell-walls, etc., which enter into its composition, by which means 

 the fat is able to mingle more uniformly with the other constituents of 

 the chyme. 



The gastric fluid acts as a general solvent for some of the saline con- 

 stituents of the food, as, for example, particles of common salt, which 

 may happen to have escaped solution in the saliva; while its acid may 

 enable it to dissolve some other salts which are insoluble in the latter or 

 in water. 



e. Upon starches the gastric juice has no action, but by the aid of its 

 hydrochloric acid it inverts the disaccharides into monosaccharides to a 

 certain extent, changing cane sugar into dextrose ; the ferment glucose (if 

 existent) may have a similar, though unimportant and slight, action. 



g. The action of the gastric juice in preventing and checking putre- 

 faction has been often directly demonstrated. Indeed, that the secretion 

 which the food meets with in the stomach is antiseptic in its action, is 

 what might be anticipated from the proneness to decomposition of organic 

 matters, such as those used as food, especially under the influence of 

 warmth and moisture. It is due to the antiseptic action of the gastric 

 juice that disease-germs are often destroyed in the stomach, and the per- 

 son is saved from an attack of illness. 



Time occupied in Gastric Digestion. Under ordinary conditions, from 

 three to four hours may be taken as the average time occupied by the 

 digestion of a meal in the stomach. But many circumstances will modify 

 the rate of gastric digestion. The chief are : the nature of the food taken 

 and its quantity (the stomach should be fairly filled not distended) ; the 

 time that has elapsed since the last meal, which should be at least enough 

 for the stomach to be quite clear of food ; the amount of exercise previous 

 and subsequent to a meal (gentle exercise being favorable, over-exertion 

 injurious to digestion) ; the state of mind (tranquillity of temper being 

 essential, in most cases, to a quick and due digestion), and the bodily 

 health. 



Movements of the Stomach. The gastric fluid is assisted in accom- 

 plishing its share in digestion by the movements of the stomach. In 

 granivorous birds, for example, the contraction of the strong muscular 

 gizzard affords a necessary aid to digestion, by grinding and triturating 

 the hard seeds which constitute part of the food. But in the stomachs of 

 man and other Mammalia, the movements of the muscular coat are too 

 feeble to exercise any such mechanical force on the food; neither are 

 they needed, for mastication has already done the mechanical work 

 of a gizzard; and experiments have demonstrated that substances are 



