Reference must be made to various conditions which interfere with normal digestion. One of the commonest is unduly hurried meals. The bolting of imperfectly masticated food is a fruitful cause of indigestion. Irregularity in meals is another factor which may derange digestion. This irregularity may take the form of unequal and irregular hours between meals, as, for instance, allowing six hours to elapse between the first and second meal of the day, and three hours between the second and last, or it may take the form of want of regularity in the size and nature of the meals, as the partaking of a heavy middle-day meal by a person who has accustomed himself to a light luncheon in the middle of the day. Constipation interferes with healthy digestion, more especially if it be associated with auto-intoxication such as frequently arises from altered bacterial activity in the digestive tract, the result of a septic condition of the teeth (oral sepsis). Lack of appetite may lead to a weakening of the digestive powers, but in this connection we have to note that in some people the introduction of food into the stomach seems to induce an appetite. A sudden change in diet may adversely affect digestion. The researches of Pawlow have shown that the digestive juices adapt themselves in a remarkable manner to the kind of food - a protein diet leading to the development of juices specially adapted for the digestion of proteins, a carbohydrate diet similarly inducing secretions specially adapted to digest carbohydrates. It is therefore easy to understand that any sudden and complete change of diet may for the time being interfere with normal digestion. The digestive powers may also be modified by the nature of the food. For example, a fatty diet interferes with the action of the gastric juice; excess of fluid may lead to an impairment of its action, through over-dilution; or new bread, new potatoes, and the like may throw a strain on the gastric secretion which it is unable adequately to deal with. The temperature of the food is of some importance, hot food stimulating the flow of the salivary and gastric secretions, iced foods sometimes arresting the digestive process, especially when taken immediately after hot foods. Lastly, active physical or mental work should be avoided during the earlier stages of digestion, as the blood is then primarily required for the digestive processes.
Sleep is affected by the quantity and kind of food taken. A heavy meal taken shortly before going to bed may be followed by a disturbed and restless night, and sleep of an unrefreshing character. As it ordinarily takes three hours to complete gastric digestion, that time at least should elapse between the last regular meal of the day and bedtime. Many patients find that their sleep is disturbed after taking certain articles of food or drink in the preceding afternoon or evening, e.g., strong tea or coffee, new scones, and the like. On the other hand, sleeplessness is often observed in elderly subjects who have taken only a light evening meal, and may be promoted by taking a little fluid food at bedtime, e.g., cup of hot beef-tea, malted milk, or thin gruel.
Dr Reid Hunt1 has recently made a valuable contribution to our knowledge of the specific action of various foods upon the resistance of animals to certain poisons. Dr Hunt's earlier experiments showed some very striking alterations in the resistance of animals to certain poisons produced entirely by changes in diet, animals on certain diets being able to resist as much as forty times the amount of certain poisons fatal to animals fed upon other diets. The results obtained by Dr Hunt were attributed by him largely to a specific action of the diet upon the thyroid gland, and they confirm in a striking manner the results of the author's experimental observations in illustrating how an internal secretion may be modified in a definite manner by diet (see Appendix). Dr Hunt's experiments are of much value in suggesting new lines of research by the experiment.il method.
1 Bulletin No. 69, Hygienic Laboratory, U.S. Public Heulili Institute, Washington, 1910.