Food being the appropriate stimulus of the secreting vessels of the stomach, the moment the alimentary morsel comes into contact with the mucous membrane, the action of the latter, as was formerly pointed out, becomes increased; its bloodvessels are distended, its colour deepens to a brighter red, and the gastric juice immediately begins to be poured out. The muscular fibres of the stomach, being acted upon by the same stimulus, next come into play, and execute their specific function of alternate contraction and relaxation. By these means the aliment speedily becomes impregnated with the gastric fluid and undergoes the influence of that continued gentle agitation already described as essential to digestion, and which seems to have for its chief object the careful admixture of every portion of the nutriment with the quantity of gastric juice necessary for its solution. The particles of food are thus continually changing place, and if the quantity taken be not too great for the power of the gastric juice which the stomach can supply, chymification goes on equally throughout; so that, if the contents of the stomach be withdrawn in from thirty minutes to an hour after a moderate meal, they will be found to consist of perfectly formed chyme and particles of food, intimately mixed and blended, in larger or smaller proportions, according to the vigorous or enfeebled state of the digestive organs, and the quality of the aliment itself. So effectually indeed has the admixture of food and solvent juice taken place in this short time, that, as already shewn, when a portion is removed from the stomach and placed in an appropriate vessel, digestion will commonly continue in it, provided it be placed in a proper temperature, and subjected to gentle and continued agitation. It is the impossibility of its being adequately acted upon by the muscular contractions of the stomach, which renders fluid and highly concentrated nourishment, when exclusively used, so difficult of digestion; and hence the reason why a certain bulk and consistence given to whale oil, for example, by the admixture of such innutritious substances as vegetable fibre, bran, or even saw-dust, make it a more acceptable and digestible article of food to the inhabitants of the northern regions, than when it is consumed in its pure state. In like manner, in civilized society, bread, potatoes, and vegetables, are useful, not less by giving the requisite bulk and consistence to the rest of the food, than by the nutriment which they contain. Soups, jellies, arrow-root, and similar substances, are, for the same reason, more easily digested when eaten along with bread or some bulkier aliment, than when taken alone, especially if used for some time.