

DIGESTION. 



DIGESTION. 



310 



the tab* by a powerful contraction upon it of the strong fasciculi of 

 mtucular fibre* of which it u composed. 



By th* ooaophafTM the food u conveyed into the stomach, where it 

 U converted into a laid Urmed Chyme. The chyme when duly pre- 

 pared in the tomaeh U transmitted to the nll intestine*, in the 

 timt portion of which it i* oonTorted into a new subntauce called Chyle. 

 In iu paasag* along the teoond portion of the small intestine* the 

 chyle disappear*, being taken up by a set of vessel* named lacteal*, 

 which conrey it through a double aerie* of glands, called the Mesen- 

 terio Olanda, to the Thoracic Duct. By the thoracic duct it i* conveyed 

 through the abdomen into the thorax, where it u poured into one of 

 the large veins, the Bubdavian, which return* the blood from the 

 upper parU of the body to the right tide of the heart, to be, by the 

 heart propelM into the Pulmonary Artery. By the pulmonary 

 artery the chyl*, DOW mingled with venoun blood, i conveyed to the 

 lung*, where it undergoes its ultimate change, and is converted into 

 arterial blood. The Urge intestinal meantime carry out of the body 

 that portion of the food which ha* not been converted into chyle. 

 All solid food undergoes the same process. [FoOD.] 



The food torn, as has been stated, into minute fragment* by tho 

 operation of mastication, softened and brought into the state of a pulp 

 by it* admixture with mucus and saliva, and raised nearly to the tem- 

 perature of the blood by the warmth of the mouth, is received into .an 

 extensive chamber, the stomach, when it is constantly maintained at 

 a temperature of 100 of Fahrenheit, and kept in a state of gentle but 

 almost unceasing agitation by a peculiar motion of the stomach, 

 effected by its muscular fibres, and called, from its striking resem- 

 blance to the motion of the earthworm, peristaltic. The essential phe- 

 nomena which take place on the introduction of the food into the 

 stomach are the following : 



The food on entering the stomach U not arranged indifferently in 

 any part of the chamber, but is detained in the great extremity, or 

 that portion of the stomach which is near the entrance of the oesopha- 

 gus, termed the cardiac extremity. This portion of the stomach 

 during the actual process of digestion appears to be cut off from the 

 rest by a contraction of the circular fibres of the muscular coat, called 

 the hour-glass contraction, by which about a third of the length of 

 the stomach towards its small or pyloric extremity is separated from 

 the great .or cardiac extremity. The food received in the cardiac 

 extremity is slowly dissolved ; this solution takes place at the surface ; 

 " iu proportion as it proceeds the dissolved part is rolled off the rest 

 by the peristaltic action of the fibres of the stomach, and carried to 

 the pyloric portion," where it accumulates. Thus the undissolved 

 and the dissolved portions of the food arc in different parts of the 

 stomach ; the undissolved portion in the cardiac extremity, and the 

 dissolved portion in the pyloric extremity. 



A remarkable change takes place on the inner or mucous surface of 

 the stomach the moment a portion of food comes in contact with it 

 This change ha* been seen to take place in the stomachs of animals 

 laid open during the process of digestion for the purpose of affording 

 an opportunity to observe the phenomena, and even in the human 

 tomaeh, which, in more than one instance, ha* been completely 

 exposed to view in consequence of wounds accidentally inflicted. 

 The mucous coat of the stomach, which is of a pale pink colour when 

 the (tomaeh i* empty, becomes of a bright red colour when excited 

 by the contact of food. Over this reddened surface are visible, more 

 especially when it is examined through a magnifying glass, innumer- 

 able minute lucid points, from which distils a pure limpid and colour- 

 lews fluid. This fluid, as it i* discharged, is absorbed by the aliment 

 in contact with the surface of the stomach, or collects in small drops 

 and trickles down the sides of the stomach to the more depending 

 part*, and there mingles with the food and dissolves it This fluid, 

 the true solvent of the food, U termed the Gastric Juice or Acid. It 

 ha* been ascertained to be the efficient agent in digestion, and it* 

 solvent power ha* been demonstrated by a aeries of most decisive 

 experiments long ago performed by Spallanzani and others. This 

 distinguished physiologist (wallowed a metallic tube perforated with 

 hole* and Ailed with flesh ; be allowed the tube to remain in the 

 stomach four hours, and then contrived to throw it up by exciting 

 vomiting mechanically. The flesh in the tube was found to be tho- 

 roughly soaked with the fluid of the stomach ; ita surface was in a 

 dissolved rtate, being soft and gelatinous, and moreover it had wasted 

 from 3 to 88 grain*. Subsequently, Dr. Stevens induced a person 

 practiced in swallowing pebbles, to swallow a hollow silver sphere 

 containing raw or cooked flesh, or vegetable*, and perforated with 

 holt* that would admit a crow-quill : the sphere was voided in about 

 forty hours perfectly empty. Next, Mr. Hunter observed that the 

 great extremity of the human itomach i* sometimes found after death 

 in a softened state and even in a state of partial solution, the coats of 

 the stomach being dissolved by its own gastric juice, and the edges of 

 the opening appearing pulpy, tender, and ragged, and even the parts 

 adjacent to the itomach, a* the ipleen, the diaphragm, and the lungs 

 being in like manner softened. 



More recently, Dr. Beaumont, an American physician, has performed 

 a neric* of experiment* on the digestibility of various kinds of food 

 by introducinic food directly into the stomach of a man Martin St 

 Ann who had a fictitious opening into that organ through the 

 paneto* of the abdomen. The result* of his experiment* are interest 



ng, and are given in the following table. It appear* that the articles 

 were converted into chyle, that is, digested, in the times indica- 





 30 

 45 

 

 

 

 2 45 

 2 80 



Oyster*, stewed 

 Eggs, raw . . . 

 Egg*, soft boiled 

 Eggs, hard 1> 

 Beef, roast or boiled 

 Beef, salted . 

 Mutton, roost or 1 

 Pork, boiled . 

 Pork, salt and bulled . 

 Pork, roost 

 Veal, masted 

 Turkey and Goo:-' 

 Domestic FowU . 

 Wild Fowls 



3 "0 

 6 30 

 3 



38 

 N 



30 

 30 



u 



Rice, boiled soft . 10 Oyster*, stewed . 8 30 



Apples, sweet and ripe 1 30 Eggs, raw . 



Sago, boiled . . 1 45 Egg*, soft boiled 



Bread, stale ... 20 Eggs, hard boiled . 3 30 

 Milk, boiled . 

 Cabbage . . 

 Baked Custard . 

 Parsnips, boiled . 

 Potatoes, roasted . 2 30 



Potatoes, boiled > . 3 30 

 Turnips, boiled . 3 30 



Jarrots, boiled . . 8 15 

 Butter and Cheese . 3 30 



Venison ... 1 35 

 Oy.-tcra, raw . . 23 



The solution of the food, which take* place during this process, U 

 wholly different from the spontaneous resolution which warmth and 

 moisture tend to produce in it. Exposure of the food to warmth and 

 moisture decomposes it by the process of putrefaction ; but the gas- 

 tric juice is antiseptic, and stops the putrefying process even after it 

 is considerably advanced. The solution of the food by the gastric 

 juice is a chemical operation, and the gastric juice is a chemical agent, 

 the exact nature of which is not yet clearly ascertained. Spallonzaui 

 discovered that the gastric juice is of an acid nature. Some years ago 

 Dr. Prout ascertained that muriatic acid is present If meat and 

 gastric juice be inclosed in a glass tube, and kept at the temperature 

 of the human body, a product is obtained closely resembli: i 

 formed by the solution of the food in the stomach. If meat be inclosed 

 in a glass tube with diluted muriatic acid, and kept at the tempera- 

 ture of the blood, a perfectly similar product is obtained. 



From experiments upon the dog it has been ascertained that muri- 

 atic acid is not present in the gastric acid of that animal. IU acid 

 reaction is produced by superphosphate of lime. Lactic and acetic 

 acids are also found present in human chyle. So we may state that 

 up to the present time chemistry has not been able to decide, win ; In r 

 the acid re-action of the gnstric juice depends on free acids, acid salts, 

 or acid organic compounds. 



In addition to the acid, the gastric juice contains a substance called 

 Pepsine. The properties of this substance have been principally 

 studied in that form of it obtained from the mucous membrane of the 

 pig, which is very like to that of man. [I'ni-siXK.J This substance, when 

 combined with muriatic or acetic acid, has a very remarkable power in 

 dissolving albuminous foods. "A liquid which contains only 17-ten- 

 thousandths of acetate of pepsine and nix drops of muriatic acid per 

 ounce, possesses solvent power enough to dissolve a thin slice of coagu- 

 lated albumen in the course of six or eight hours' digestion. With 12 

 drops of muriatic acid pi r mim-e, the same quantity of white of egg 

 is dissolved in two hours." (Carpenter.) These properties quite 

 explain the action of the gastric juice upon the food. 



After the food has undergone the action of the gastric juice, it loses 

 it* sensible properties, and is converted into the homogeneous semi- 

 fluid mass which has received the name of chyme. Specific differences 

 are distinguishable in chyme, according as the food from which it is 

 formed has consisted of vegetable or animal matter, and according as 

 it has contained fatty or oily substances, or has been destitute of them. 

 Usually however it consists of a pultaceous mass of a grayi.-h i uli.ur ; 

 it ha* a sweetish taste, and is slightly acid. The character common 

 to it, from whatever kind of food it may have been produced, and 

 therefore distinctive of it, is its acidity. 



The state of the food in the chyme has not been clearly made out. 

 Dr. Carpenter gives the following account : 



" The protein compounds, whether derived from animal or vegetable 

 food, are all reduced to the condition of albumen ; a part of which U 

 dissolved, whilst another portion is suspended iu a MTV 

 divided state. Gelatine will be dissolved or not, according to its ' 

 previous condition; if it exist iu a tissue from which it cannot readily 

 be extracted it will pass forth almost unchanged, but when ingested 

 in a state of solution it remains so, and if it have been previously 

 prepared for solution by boiling, its solution is completed in the 

 stomach. The gummy matters of vegetables are dissolved \vlmi 

 they exist in a solilblo form, as in tho case of pure gum, pectiuo, and 

 dextrine, or starch-gum. The degree iu which starch, when its 

 vesicles have not been ruptured by heat, is nt!i<tl !>y the gastric 

 fluid, seems to differ in different animals; tho Ruminants and Omni- 

 vorous Birds apparently possessing the power of crushing or 

 dissolving the envelopes of the starch globules, whilst they pass 

 through the alimentary canoJ of other Jlcrbirora unchanged, and 

 may be detected entire in their excrements. Sugar is unquestionably 

 taken up in solution, as such, in a healthy condition of the system, 

 but it may undergo a previous change in the stomach in disordered 

 states of the digestive process. Oily matters \ihrilni- .;!' animal .,; 

 vegetable origin, are reduced to the condition of an emulsion, being 

 very finely divided, and their particles diffused through the i-l 

 Most other substances, a* resins, woody fibre, horny matter, yellow 

 fibrous tissue, 4c., pass unchanged from tho stomach, and undergo no 



