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Kai Tiaki : the journal of the nurses of New Zealand, Volume XIV, Issue 2, 1 April 1921, Page 85

Hydrochloric acid is not a ferment, but is a most important adjunct m gastric digestion: (1) Activates pepsin; (2) helps m the inversion of sugar; (3) acts as a disinfectant, and kills bacteria. SUMMARY OF THE " DIGESTION ?? PROCESS. Mouth. — Food is collected into a bolus by tongue and cheek; broken by teeth, moistened by saliva action, voluntary; may be performed involuntarily. Mechanical Action. — Food passes into the pharynx, which contracts and forces it down the oesophagus. It passes along the oesophagus with a peristaltic movement. Enters the stomach; action, involuntary; Chemical Action. — The carbohydrates are acted upon only, starch being turned into sugar by the ferment ptyalin m the saliva. Stomach. — Mechanical Action : The stomach (1) connects oesphagus with small intestine; (2) holds food while it undergoes chymiflcation ; (3) secretes fluids necessary for that ac-

tion. Peristaltic action of the stomach is continued involuntarily during digestion. Chemical Action. — Dissolves nitrogenous foods — that is, the gastric juice by its ferment pepsin turns proteins into peptones. These peptones are at once fit for absorption, and are to a certain extent taken up by the mucus membrane of the stomach, and passed into the blood. The ferment rennet coagulates milk. No action on starchy (carbohydrates) food. The digestion of carbohydrates m the stomach is continued by the swallowed saliva until the ptyalin is rendered inactive by the moisture of the gastric juice. No action on fats beyond breaking them up. Hydrochloric acid m the stomach plays an important part m gastric digestion. The partly-digested food 'is now called chyme. Small Intestine. — The chyme passes through the pyloric orifice into the duodenum. Tt is m the small intestine that the greatest amount of digestion and absorption takes place.

Mechanical Action. — (1) Peristaltic movement. (2) A series of local constrictions which forces it into the folds and against surface of valvular conniventes, thus assisting m mixing the digestive juices and aiding m its absorption. The interior surface of the small intestine is covered with minute projections called villi, which are engaged m absorption. Chemical Action. — Two small ducts enter the duodenum. One brings the bile from the gall bladder, and the other, from the pancreas, bringing the pancreatic juice. Small Intestine.! — The i ' succus intericus M is secreted by the duodenal glands, and by the simple follicles which are scattered all through the small intestine. The mechanism of its secretion is very imperfectly known. The ferments contained act on all foods. Bile emulsifies the fats, aids m their absorption, lubricates the intestinal w^alls, acts as an -antiseptic. Pancreatic juice contains three ferments: (1) Amylopsin acts on carbohydrates; (2) Trypsin acts on proteins; (3) Steapsin. or Lipase, acts on fats. Sugars, like fats, undergo little change until they meet the ferment m the duodenum. The milky-coloured emulsion, as the result of the digestion of fats, is now called chyle. Large Intestine. — Food substances not absorbed m the small intestine pass through the ilea-cecal valve into the cecum. Mechanical Action.— Peristaltic movement, both a backward and forward movement m this intestine. Large Intestine. — The large intestine has no ferments necessary for the digestion process. Chemical Action.— The digestion carried on is due to the presence of bacteria and to the succus intericus, with w^hich the food became mixed m the small intestine. Bacteria. — Bacteria are always present m the intestine, and take an active part m the breaking-up of food substances. Absorption is continued m the large intestine.

Defacation. — The waste products are discharged from the body through the anus. This waste consists of solid residue called fasces. How the Now Digested Food Enters the Blood. — The passage of the nutritious substances from the digestive -canal to the blood system constitutes the process called absorption. Absorption by Blood-vessels. — The whole of the alimentary canal is lined with mucus membrane containing the minutest blood-vessels (capillaries), and as soon as food is digested it begins to penetrate through the thin walls of these blood-ves-sels. (1) Every kind of food is absorbed if dissolved. (2) No power of selection. The Lymphatic System. — Another process of absorption is called the "lymphatic system/ so called because its vessels contain watery fluid during fasting. It consists of (1) lymphatic capillaries; (2) lymphatic vessels ; (3) glands; (4) two lymphatic trunks, the larger being called the thoracic duct, situated behind the thorax. The lymphatic capillaries originate m the organs and tissues of nearly every part of the body. Those m the small intestine are called lacteals. The minute, hairlike projections m the small intestine are called villi. Each villus is supplied with one or more lacteals, besides a network of blood capillaries. Hence absorption goes on. rapidly here. Absorption by lacteals differs from that by blood-vessels, because they have the power to select the fatty substances. Blood-vessels. — The blood-vessels are responsible for the absorption of the chief part of the peptones, the sugar and salts, and a little of the fats. Lacteals.— The lacteals carry into the blood the principal part of the fat, and a small quantity of peptones. It is carried to the thoracic duct and emptied into the left innomonate vein, and thus enters the blood. Other lymphatics absorb the fluid portion of blood (lymph) which has exuded through the blood-vessels.

The glands are engaged m elaborating blood from lymph and chyle. Receptaculum Chyli. — The thoracic duct lies m front of the vertebral column. Its lower end, situated m the abdomen, is very wide, and is called the receptaculum chyli. It receives lymph and chyle and pours them into the blood system.

The changes that occur m foodstuffs from the time they are absorbed to the time they are eliminated m the excretion are called metabolism. [Finis.] R. E. de WARREN. Wellington Hospital, June, 1920.