820 



DIGESTION 



DIGIT 



frequently found to disagree with some stomachs ; 

 but even in such cases it may often be ' sipped ' 

 with impunity. In this case the formation of 

 large clots is prevented. Lime-water causes the 

 milk to coagulate in small soft clots. 



The products of digestion, peptone and sugar, 

 together with water and many soluble salts, 

 are absorbed into the blood-vessels which ramify 

 in the gastric mucous membrane. When gastric 

 digestion is over, the undigested food (chyme) 

 passes through the relaxed pyloric sphincter 

 into the small intestine. The chyme consists 

 of some proteid and starchy matter, together with 

 fat and oil and indigestible substances such as 

 vegetable fibre, pure wax, cartilage, &c. mixed 

 with gastric juice. Intestinal digestion is an 

 alkaline one, and all the digestive juices of 

 this part of the digestive system are alkaline in 

 their reaction. They soon counteract the acidity 

 of the chyme, which now becomes alkaline. The 

 proteids which remained undigested by the stomach 

 are now acted upon by a ferment called trypsin 

 found in the juice of the pancreas. This converts 

 the proteids into peptones through an intermediate 

 propeptone. The pancreatic juice contains other 

 ferments which operate during digestion, notably 

 a hydrolytic ferment, similar in its action to 

 ptyalin, whereby the remaining starch is converted 

 into sugar. The juice itself is thick and viscous. 

 It is strongly alkaline and secreted in rather small 

 quantity. It is said to possess a ferment capable 

 of splitting oil and fat into glycerine and fatty acid, 

 which it does by adding water to the fat, which is 

 then decomposed. The fatty acid unites with the 

 free alkali present, and a soap is formed which is 

 subsequently absorbed. The alkaline contents of 

 the alimentary canal also emulsify fat i.e. they 

 cause it to become very freely divided, forming 

 a milky fluid. The minute microscopic globules 

 which result pass readily through the walls of the 

 alimentary canal into the lymphatics (lacteals). 

 The emulsification of an oil can readily be shown 

 by adding about half its volume of carbonate of 

 soda (3 per cent.) solution to cod-liver oil. The 

 latter becomes at once very similar to milk in its 

 appearance. 



The intestinal juice, the secretion of Lieberkiihn's 

 follicles, is strongly alkaline. It assists in the 

 digestion of starch and of proteid matter. In 

 addition an important ferment called 'invertin,' is 

 found. This has the power of changing cane into 



grape-sugar and an allied substance, Isevulose. 

 oth these bodies have the same formula, but 

 differ from one another in their action on polarised 

 light, 



Cane-sugar. Water. Grape-sugar. Laevulose. 



CigH^On + H 2 O = C 6 H 12 O 6 + CgH 12 O 6 . 



The importance of this ferment will be appreciated 

 when we consider how large a quantity of food is 

 taken in the form of cane-sugar, and that cane- 

 sugar introduced into the blood is not of any use to 

 the body, and is eliminated at once by the kidneys. 

 The bile may be looked upon both as an excretion 

 from the body and as a digestive juice. The 

 colouring of the faeces and urine is due in part to 

 a pigment hydrobilirubin (urobilin), which is an 

 altered bile pigment. If bile is excreted rapidly, 

 the faeces are dark in colour, and they may be 

 white owing to deficient excretions. Many sub- 

 stances such as mucin, cholesterin, &c. found in 

 the bile are excreted to form part of the fasces. On 

 the other hand many bile constituents, such as the 

 bile salts, are reabsorbed and used again in the 

 economy. Bile has an important action in digestion, 

 as may be shown by making biliary fistula in dogs, 

 whereby the bile leaves the body at once through 

 an aperture in the abdomen. In this case the 



animal loses flesh ; the fat which it takes with 

 its food passes unabsorbed through its digestive 

 system, and its excretions are offensive. The bile 

 seems then to assist in fat absorption, and to have 

 some antiseptic action whereby putrefaction is 

 prevented or lessened within the digestive system. 

 Bile assists in the absorption of fat not only by 

 assisting in its emulsification, but also by helping 

 in some way or other the epithelial cells, covering 

 the villi to take up the minute fatty particles. In 

 addition it is supposed to stimulate minute muscular 

 fibres within the villi, which by their contraction 

 pump the absorbed fat on into the larger 

 lymphatics. 



Within the small intestines most of the food 

 undigested by the stomach is rendered fit for 

 absorption. This takes place through the tissue 

 of the mucous membrane ; much of the sugar and 

 peptones find their way into capillary blood-vessels. 

 Absorbed products, and notably fat globules, pass 

 into the lacteals, and thence into the blood, cir- 

 culating through the veins at the root of the neck. 

 The contents of the lacteals during absorption are 

 called chyle. The contents of the small intestine 

 pass into the large intestine, where digestion 

 occurs to a very slight extent. Absorption is, how- 

 ever, more rapid, and the contents become far more 

 solid as they pass towards the rectum, due to the 

 deprivation of water and soluble substances. The 

 absorptive power of the large intestine is important 

 to remember; for injections per rectum or liquid 

 food, especially if it has already been artificially 

 digested, may frequently sustain life for long 

 periods. 



Artificial Digestion. The digestive juices are 

 occasionally defective in amount or in quality, and 

 in this case they may be supplied artificially. All 

 the digestive ferments may be separated by very 

 simple processes from the glands which secrete 

 them, and many may readily be obtained in the 

 market. Pepsine and hydrochloric acid, taken with 

 or before a meal, are often of great service, the 

 most reliable preparations of pepsine being the 

 ordinary pepsina porci. Food may be digested 

 outside the body before its administration. Beef- 

 tea and milk-gruel may be prepared in the follow- 

 ing way : To bring the food to the proper tempera- 

 ture, boil half of it, mix it with the other half, and 

 keep warm near the fire. To this add a prepara- 

 tion of the pancreatic ferments in the proportion 

 given in the directions which invariably accompany 

 the bottle containing the substance. The food 

 should now be kept warm for an hour or so, and 

 then boiled in order to prevent any further action 

 of the ferment. It may be taken by the mouth or 

 administered as an enema. Preparations of the 

 pancreas are alone to be used in peptonising food 

 outside the body, as pepsine preparations produce 

 a bitter and unpleasant taste. Pancreatic prepara- 

 tions on the other hand are useless when taken 

 with the food, as they are destroyed within the 

 stomach. 



See many separate articles throughout this work, such 

 as those on BLOOD, CHYLE, LYMPH, BILE, SALIVA, PEP- 

 SIN, ABDOMEN, GLANDS, DIET, FOOD, COOKERY, ALCO- 

 HOL, INDIGESTION, &c. ; and the physiological hand- 

 books of Huxley, Foster, and Landois. 



Digging. See SPADE-HUSBANDRY. 



Digit (Lat. digitus, 'a finger'), a term applied 

 to the ten symbols of number, 0, 1, 2, &c. to 9; 

 thus, 305 is said to be a number of three digits. 

 Numbers were originally indicated by the fingers, 

 and hence the name. Astronomers use digit to 

 signify a twelfth-part of the diameter of the sun or 

 moon, and speak of an eclipse of seven digits, 

 meaning that seven-twelfths of the diameter is 

 covered. 



