The organs comprising this system are: the mouth, the pharynx, the gullet (foodpipe), the stomach, the duodenum, and the small and large intestines. From the viewpoint of the science of diet, the food we consume should enfold five constituents, namely, carbohydrates, proteins, fats, mineral salts, and vitamins. The first three constituents in this list are supposed to yield energy that is requisite for the life activity of an individual. One gram of carbohydrate or protein gives 4.1 calories of energy, while one gram of fat is found to give 9.2 caloriesof energy. We acquire large sum of carbohydrates from cereals, potatoes, sugar, etc. The proteins, in accumulation to supplying energy, perform another important function, that of building the muscles of the body. They are of two types, namely, plant proteins, which are contained in great quantities in pulses, and dried nuts, and animal proteins, which may be established from animal sources, like eggs, meat, fish, poultry, milk, and so on. The animal proteins are extra valuable, and hence vegetarians must contain adequate quantity of milk in their diet, so as to fulfill the requirements of animal proteins. The fats can also be...