Such an individual needs to know that one of the hardest things for the members of his family is to live day by day with one who maintains an attitude of mental depression, and he should stir himself for “his stomach’s sake,” as well as for the sake of his family, to a cheerful interest in something. He should let go his grudge and ride a hobby, if it is a cheerful one, and ride it hard.
It may be well, here, to trace, briefly, the progress of the food through the digestive tract and the action of the juices and the ferments on it.[5]
Salivary Digestion
The food in the mouth is mixed with saliva, which begins the dissolution of the starches.
The saliva consists of about 99.5 per cent. water and 0.5 per cent. solids. The solids consist of ptyalin, sodium chlorid, sodium carbonate, mucus, and epithelium. Ptyalin, the most important of these, is the active digestive agent; the mucus lubricates the masticated food; the sodium carbonate insures the alkalinity of the food, and the water dissolves the food that the juices may more readily reach and act on each particle.
The starches are the only foods whose chemical digestion is begun in the mouth. They are first broken up by the ptyalin into dextrin and then into the more simple sugar, known as maltose.[6]
It is important that sufficient saliva be mixed with the food through mastication, because unless the digestion of the starches is begun by the saliva, either in the mouth or after it is swallowed, they are not acted on until they reach the small intestine, consequently their digestion is unduly delayed. The pancreatic juice must then do more than its normal work of digestion.
The saliva flows into the mouth, more or less, at all times, but more copiously during mastication.
The movement of the jaws in chewing incites its flow and when starches are not well digested, gum chewing, in moderation, though not a refined habit, is beneficial.