163. Effect of Occupation. Occupation has an important influence upon the quantity of food demanded for the bodily support. Those who work long and hard at physical labor, need a generous amount of nutritious food. A liberal diet of the cereals and lean meat, especially beef, gives that vigor to the muscles which enables one to undergo laborious and prolonged physical exertion. On the other hand, those who follow a sedentary occupation do not need so large a quantity of food. Brain-workers who would work well and live long, should not indulge in too generous a diet. The digestion of heavy meals involves a great expenditure of nervous force. Hence, the forces of the brain-worker, being required for mental exertion, should not be expended to an unwarranted extent on the task of digestion. 164. Effect of Climate. Climate also has a marked influence on the quantity of food demanded by the system. Much more food of all kinds is consumed in cold than in warm climates. The accounts by travelers of the quantity of food used by the inhabitants of the frigid zone are almost beyond belief. A Russian admiral gives an instance of a man who, in his presence, ate at a single meal 28 pounds of rice and butter. Dr. Hayes, the Arctic traveler, states from personal observation that the daily ration of the Eskimos is 12 to 15 pounds of meat. With the thermometer ranging from 60 to 70° F. below zero, there was a persistent craving for strong animal diet, especially fatty foods.[24] Illustration: Fig. 63.—Lymphatics and Lymphatic Glands of the Axilla. The intense cold makes such a drain upon the heat-producing power of the body that only food containing the largest proportion of carbon is capable of making up for the loss. In tropical countries, on the other hand, the natives crave and subsist mainly upon fruits and vegetables. 165. The Kinds of Food Required. An appetite for plain, well-cooked food is a safe guide to follow. Every person in good health, taking a moderate amount of daily exercise, should have a keen appetite for three meals a day and enjoy them. Food should be both nutritious and digestible. It is nutritious in proportion to the amount of material it furnishes for the nourishment of the tissues. It is digestible in a greater or less degree in respect to the readiness with which it yields to the action of the digestive fluids, and is prepared to be taken up by the blood. This digestibility depends partly upon the nature of the food in its raw state, partly upon the effect produced upon it by cooking, and to some extent upon its admixture with other foods. Certain foods, as the vegetable albumens, are both nutritious and digestible. A hard-working man may grow strong and maintain vigorous health on most of them, even if deprived of animal food.