=Conditions Requisite for Normal Digestion.=—When M. Chevreul, Professor of Chemistry at the Jardins des Plantes of Paris, attained his hundredth year, an interviewer very naturally inquired of him, “Have you always had a good digestion?” To this the still vigorous Professor answered: “I really cannot say, for I have never noticed.” So long as it is well used, the stomach is an unobtrusive organ. It is tyrannical when it deems itself the victim of inconsiderate treatment. A study of its physiology serves to show that it will work contentedly only upon certain clearly defined terms, of which the following are perhaps the most important: The stomach exacts due warning that its services are wanted. The nerves of smell and taste must announce the approach of food and guarantee its quality. “What may I eat?” asked a large-framed, strenuous, eager, overworked barrister of a great physician. “Eat, sir? You may eat whatever you like. But be quite sure that you do like it.” Wise advice. The human race would not have developed its strong preferences for certain kinds of food if all foods were equally suitable to satisfy its needs. Taste is not a matter of fashion. It is the expression of the experience of mankind. Fanciful as civilization has made us, and easily as appetite is perverted, if we are sure that we really like, and want, a food, we may trust that our liking will guide us as safely as it guides a buffalo or a deer. “Eat what you like.” Eating with liking carries with it the idea of obtaining the maximum of satisfaction from the exercise of this necessary function. Most things which are reckoned unwholesome are full in flavour or rich in consistency. They satisfy the palate when spread out very thin. It is poor economy to help oneself to caviare with a table-spoon. In the second place, the stomach must be assured that the teeth are doing their proper share of work. Among the many half-truths which every year are exalted to the level of a revelation or a rule of conduct is the doctrine of the “chewers”—persons who take no meals, but industriously and almost continuously masticate nuts and biscuits. Thirdly, the meal must not be so large that the stomach cannot deal with it “at a sitting.” In from two to three hours the last of the food should have passed through the pylorus, allowing the stomach to rest before it is called into activity again. As proteins are practically the only foods which are digested in the stomach, the work required of this organ depends upon the quantity of proteins present amongst the constituents of a meal. Meat is the food richest in proteins, although bread, vegetables, milk, cheese also yield them. Some people can digest three meat meals every day; but others, probably the majority, find that it is unwise to take any considerable quantity of meat more than once in twenty-four hours. It is only when the cells of the gastric glands have accumulated a store of pepsinogen-granules that proteid digestion is vigorously carried on. Fourthly, the food must be in a form in which it does not irritate the stomach, provoking an outflow of acid out of proportion to the pepsin which accompanies it. Experience alone can teach the foods which are to be avoided on this account. But speaking generally, it may be said that the stomach resents the presence of substances which cannot be amalgamated into chyme. Its task is the reduction of the mixture of foods which compose a meal to the consistence of a smooth cream. Hot buttered toast or pie-crust are made of wholesome constituents enough, but, fat being melted into the starch, the fragments are impermeable to the gastric juice. They act mechanically as irritants of the mucous membrane. Again, it may be said that “pure” foods are apt to provoke acidity. Nothing could be more wholesome than eggs or pounded meat or custard pudding; but taken by themselves these articles of diet over-stimulate the mucous membrane. They need to be diluted with starch-foods, or even with cellulose.