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SOLID FOOD, ITS ELABORATION AND DESTINATION.

Liquid food introduced into the mouth is swallowed at once and passes into the stomach. If solid, it has to undergo the preliminary process of mastication. During mastication it is freely mixed with the alkaline saliva, which is poured out in abundance from the salivary glands, and which much facilitates the process. Liquid food passes into the stomach with comparatively little admixture of saliva. Solid food, on the contrary, whilst being ground and divided, is saturated with salivary secretion, which gradually forms it into a pulp fit for the action of the gastric juices. From the various experiments that have been performed, it would appear that the subsequent changes produced in solid food by the stomachal digestion are much facilitated by the presence of the saliva.

The saliva also appears to have a peculiar power of transforming the amydon or starch of farinaceous food into grape sugar, a necessary transformation in the series of food changes. This is the more remarkable as the gastric juices do not possess this power. They appear to act more especially as a solvent of the nitrogenous food element.

As soon as food reaches the stomach its presence determines the secretion of the gastric juice, which is not found in that organ during the period of vacuity or repose. This secretion exercises a very peculiar dissolving power over the food which is submitted to its action, gradually reducing it to the condition of a grey creamy or pultaceous fluid. The time employed to effect this dissolution varies according to the nature of the food; animal substances, as a rule, taking longer to digest than vegetable.

The period of stomachal digestion is one of great vital activity for that organ. The contact of food with the coats of the stomach is immediately attended with an influx of blood to its mucous membrane, which becomes highly vascularized. In this mucous membrane are innumerable glands, imbedded as it were in longitudinal bundles in its tissue, with their orifices opening on its surface. These minute glands secrete the gastric juice, which they accomplish by the successive formation and rupture of the cells that contain it. The muscular structures of the stomach are at the same time contracting actively, so as to bring successively each portion of the food in contact with the mucous membrane from which gastric juice is pouring uninterruptedly these contractions also carry off, towards

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the pylorus and intestines, that portion which has been dissolved and elaborated.

The gastric juice is acid, a property it owes to its containing lactic or hydrochloric acids, and the superphosphate of lime. Its digestive properties depend on a peculiar animal matter, to which the name of pepsine has been given, and which may be extracted in the shape of an amorphous powder. A solution of pepsine will dissolve meat or any other alimentary substance at a temperature similar to that of the body.

When empty the stomach, which may be termed in some senses a large muscle, contracts on itself; when it contains solid food it contracts firmly on the food, and forces it round and round the large curvature of the stomach, and then back to the œsophagiac orifice by which it entered. As the food dissolves and assumes the character of a creamy pultaceous fluid, which is termed chyme, it escapes from the above-described circuit, is directed towards the pylorus, and passes into the intestines. Fluids are, in a great measure, directly absorbed by the walls of the stomach, which sift out and retain their solid constituents.

The time employed by the stomach in thus digesting or dissolving food varies according to its nature,

and according to the individual. Various means have been resorted to with a view to solve this

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question animals have been killed at different hours after the ingestion of food; food has been placed in hollow perforated balls and tied to å string, by means of which they could be withdrawn at any time; or vomiting has been artificially induced. The most conclusive experiments, however, were those of Dr. Beaumont, of New York, on a young Canadian, which have been quoted by all recent physiologists. Dr. Beaumont's patient, a healthy young man, had received a gunshot wound just over the stomach, which exposed and opened that organ. The wound, on healing, left a wide fistulous perforation, which had to be closed artificially. On removing the plug or artificial covering the food could, at any period of digestion, be removed and examined, and the state of the stomach and of its secretions could be investigated.

Dr. Beaumont went through a very extended series of observations with his patient, and came to the conclusion that cooked vegetables and fluid animal substances were easier and sooner digested than flesh; and that the comparative rapidity of the digestive process depends principally on the degree of cohesion of the tissues exposed to it, that

is, on their tenderness or toughness.

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to the table published by Dr. Beaumont, the following were the principal results noticed :—rice and tripe were digested or chymified in an hour; eggs, salmon, trout, apples, and venison, were digested in an hour and a half; tapioca, barley, milk, liver, fish, in two hours; turkey, lamb, potatoes, in two hours and a half; fowls, beef, and mutton, in three hours and a half; veal in four hours. The same results were obtained on macerating these substances in the man's gastric juice, out of the stomach. The results obtained by other observers have varied, more or less, according, no doubt, to individual idiosyncrasy or peculiarities, and to the state of health at the time of the experiments. From my own experiments and observation, principally directed to the state of the urine after food, I think I am warranted in giving the following list as a guide to be generally relied on in estimating the comparative digestibility of different articles of food: milk, eggs, broths, and light soups, cooked vegetables, fish, fowl, game, lamb, mutton, veal, beef, salted meat, including ham and bacon. The time occupied in the digestion of these alimentary substances, before they reach the blood, and modify the urine, varies from two hours for the lighter food-eggs, milk, broths,

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