II.—_Occupation._ Although muscular exercise is not associated with an immediate increase of elimination of urea, yet as a matter of experience more nitrogenous food is required and can be metabolised by hard workers than by idlers. The trappers on the North American prairies can live for weeks together on meat alone, accompanied by copious draughts of tea. They are constantly in the open air, undergoing fatiguing exercises, in a dry and rare atmosphere. For brain workers no special food is required. Foods containing phosphorus have no special value, so far as is known, for mental work. Such work, however, is apt to affect digestion; consequently the digestibility of food is more important for those engaged in sedentary occupations than its chemical composition. III.—_Sex._ As a rule, women require about one-tenth less food than men, but probably this rule hardly holds good in the case of women engaged in laborious work. IV.—_Age._ Infants require only milk, and the less they have of any other food before a year old the better. Atwater has calculated that—— A child under 2 requires 3∕10 the food of a man doing moderate work. „ of 3 to 5 „ 4∕10 „ „ „ „ „ of 6 to 9 „ 5∕10 „ „ „ „ „ of 10 to 13 „ 6∕10 „ „ „ „ A girl of 14 to 16 „ 7∕10 „ „ „ „ A boy of 14 to 16 „ 8∕10 „ „ „ „ Vital processes are more active in early life, and food is required not only to carry on the functions of the body, but also to furnish the materials for growth. Hence, while the proportion of proteids to carbohydrates and fats should be— As 1:5.3 in adults, it should be about as 1:4.3 in children. After the age of thirty-five or forty, the tendency is to take too much food. All the tissues of the body are established, and excess of food (especially nitrogenous food) is liable to produce tissue degeneration by loading the system with partially metabolised matter, and may lead to gouty diseases. It is much safer to take what may be regarded as too little than too much food after this period. =Times for Eating.=—The best arrangement seems to be to have three meals, each fairly nutritious, and containing all the constituents required. The Romans only had two meals daily, prandium and cœna. This is common among the French at present, but it tends to overloading the digestive organs at these meals. An ordinary full meal has usually passed from the stomach in four hours. Fresh food ought never to be introduced before this period; it is advisable to allow an interval of five hours between meals for the healthy, so as to give time for the digestive organs to rest, and for the absorption of food. The practice of taking tea with the chief meal, or a “meat tea,” is bad. Tea is better taken an hour or two after food.