Ihere are three pairs of salivary gl«;:ncls— the parotid glands lie in front of the cars, the sub- lingual glands lie under the tongue, and the submaxillary glands under the lower jaw. In the disease called mumps it is these glands which are affected and become tender and swollen. The saliva is a clear, colourless, alkaline fluid, and the invisible ferment it contains is called " ptyalin." This ptyalin has the power of chemically changing starch into sugar. If you chew white bread, which largely consists of starch, for long enough, a sweet taste is felt in the mouth because a certain amount of the starch has been changed into sugar. These remarks ought to impress all who read them with the importance of chewing food. The longer the food is chewed, the more starch is changed into sugar. The people who bite and swallow their food without chewing sufficiently are not allowing time for digestion in the mouth. One result of this is that the stomach is over- worked. It has to do the larger part of the work of the teeth. Another point is that whenever the mass of food passes into the stomach, the digestion of starch is stopped. The stomach does not act on starch, but deals with another part of the food — viz., the proteids. Dis^estion in the Stomach The food remains in the stomach about four hours, and all the time it is being rolled over and over and churned into minute particles, because the stomach is really a muscular bag. In the wall of the stomach are innumerable minute glands which secrete gastric juice. About fourteen pints of this juice are poured out daily by the glands into the stomach. This gastric, or peptic juice pours from these glands when the food reaches the stomach, and is mixed with the food, just as the saliva is in the mouth. Gastric juice is a clear, colourless fluid, slightly acid, because it contains a minute quantity of hydrochloric acid. It also contains a ferment called pepsin, which can act upon insoluble proteid matter (which lean meat, cheese, lentils, etc., largely consist of), and change it into a soluble proteid called peptone. This may be called the process of " peptonisation of the food." If you were to put a little lean meat, cheese, and a spoonful of cooked lentils into a tumbler, and add to it either gastric juice extracted from the stomach of an animal, or simply water with a little hydrochloric acid and some pepsin, what would take place ? The meat, cheese, and lentils, which would be practically unaltered in ordinary water, would gradually be dissolved. That is what takes place in the stomach. After a few hours' digestion, the food is broken up into a semi-solid substance called " chyme," which is simply food partly digested. The 361 MEDICAL digestion of meat is carried on to a considerable extent in the stomach. Also the vegetable proteids, egg albumen, lentils, cheese, etc. These proteids, or albuminous foods, arc now converted into peptones, which are soluble in water, and rapidly pass through the thin membranous walls of the blood-vessels. Whilst the stomach is churning and digesting the food, the openings at either end of the stomach are closed, but as soon as the chyme is formed the opening into the smaller intestine relaxes. The time occupied by digestion, of course, varies with the articles eaten. Fish and lightly cooked eggs take much less time to digest than roast beef or pork, but the average time for the digestion of a meal may be said to range from three to five hours. Table Showing Time for Digesting Different Focds FISH White fish (haddock, sole, whiting) One hour Salmon and Trout . . One hour and a half Shellfish One hour and a half MEAT Tripe One hour Sweetbreads One hour Boiled chicken . . . . One hour and a half Fricasseed chicken . . Two hours and a half Liver . . Two hours Venison One hour and a half Game Two hours Lamb . . Two hours and a half Turkey , . Two hours and a half Beef and mutton , . . . Three hours and a half Salt beef Four hours and a half Pork {roast) Five hours OTHER ARTICLES OF DIET Rice {boiled) One hour Raw eggs . . . . , . One hour. and a half Cooked eggs Three hours A pples . . . . . . . . One hour and a half Milk Two hours Tapioca and barley . . Two hours Digestive power varies according to age and health. Well-cooked food is more easily digested. Warm food is more easily digested than cold food. A moderately sized meal is more quickly digested than a large meal. Thorough mastica- tion hastens digestion. Now we have considered ( i ) mouth digestion, when starchy foods are acted upon ; (2) stomach digestion, when albuminous, or proteid foods are digested. The other great group of food-stuffs which we have to consider are the fats. Fats undergo no change either in the mouth or stomach, but, as will be shown in the next article on this subject, they are emulsified in the intestines 7^0 be continued. COMMOM AHLMIEMTS AND TH^IR TREATMENT ■ Contintied from BPOnchitis, Chronic. Bronchitis may become chronic at any age, but it is most commonly found in elderly people, especially those who are gouty or subject to Bright's disease. It is often associated with heart affection. The sufferer from chronic bronchitis is very often stout, with a florid complexion, short of breath, and wheezy of respiration. The symptoms. pa^e 211, Part 2 especially the cough, are generally more marked in winter, and improve in warmer weather. " Winter cough," complained of by so many elderly people, is simply a bronchitis which comes on whenever the weather becomes cold and damp. If heart strain is avoided, and care is taken to avoid exposure and fatigue, chronic brorchitis cannot be considered very serious. It
