At the same time, the supply and consumption of nutrients should balance almost exactly for periods of a week and approximately, day by day; excepting as there is an indication to remove an excess or make good a deficit. It is even wise to have the separate meals correspond approximately to the demands for the succeeding periods.

The young infant should spend most of his time in sleep, awakening only to nurse and remaining awake only for the short time needed for exercise. During the second and third years, the child requires about 14 hours sleep, gradually reduced to 12 by the eighth or tenth year and to 10 at the close of adolescence. The arrangement of meals and naps are discussed in the chapter on Dietetics of Infancy.

During active adult life, the amount of sleep depends to some extent upon heredity and bodily vigor but largely on the severity of mental and physical labor. Thus the overworked medical student requires more sleep than most other professional students or than the average college student. For severe mental and manual labor, ten hours' sleep are usually required. Light physical labor, routine clerical work and easy professional occupations require only 7 or 8 hours' sleep. If the work covers long hours, more sleep is required than if several hours are spent in rest. The adult, like the child, who "plays hard," either in the sense of engaging in physical sports, or games requiring close mental application or delicate training of the special senses of muscles (chess, whist, billiards etc.) or a strenuous social life, requires more sleep than the one who is in a state of mental and physical inertia when not working or sleeping.

Persons engaged in heavy manual labor, as on a farm or in a lumber camp, require a hearty breakfast and dinner, preferably served hot and a light supper. For the first two meals, it is even advisable that the food should be rather slow of digestion, since the sense of hunger and weakness, depends largely on the emptiness of the stomach. The supper on the other hand, should be light and easily digested, consisting of bread and milk, or other cereal food, with milk and eggs, fruit etc., so as not to interfere with sleep by the stimulation of metabolic products and so that no great demand for innervation shall be made on the nervous centers. Even the interruption of sleep by a full bladder and especially by one filled with urine rich in waste products and of high acidity, on account of a heavy evening meal, must be considered.

On the other hand, skilled labor, not involving great physical or mental fatigue and lasting only eight or nine hours, does not usually allow or demand a hearty, warm, noon dinner, although both breakfast and luncheon should be richer in carbohydrate and fat than those of a professional or business man. Whether the evening meal is called supper or dinner, it should be essentially a dinner served hot, eaten leisurely, and it should be relatively more hearty than for the strictly manual laborer.

Business and professional men, rising later in the morning and going to bed later in the evening, should eat a light breakfast of 500 - 700 calories, a slightly heartier luncheon and should take the principal meal at the close of the day's work, allowing four or five hours for its digestion, before retiring.

For persons of leisure, keeping late hours at night, the most convenient arrangement is a fairly hearty combination of breakfast and luncheon at ten or eleven, a dinner at five, and a light supper, not too unwholesome and with very little stimulating beverages, either xanthin or alcohol-containing, at eleven or twelve in the evening.

Business and professional men whose work is quite equally divided between the morning and afternoon, and whose social life is relatively simple, should, if possible, take the leisure for a warm noon meal, the dinner and supper or luncheon and dinner, being nearly equal in amount and variety.

There is no physiologic absurdity in dividing the day's sleep and work into two equal portions, as is the custom in many barbarous countries, and in certain vocations, as on the sea. In such cases, the meals would naturally arrange themselves into two sets of breakfasts and luncheons, or suppers, with no single hearty meal.

In case of loss of sleep, it is better to make it up as soon as possible, skipping breakfast, for example, rather than to shorten the sleep for the sake of adhering to a regular schedule.

Night workers usually go to bed as soon as possible after finishing their day's work and take their recreation before it begins. Manual laborers require the same arrangement of meals, at opposite hours, as day laborers. Business and professional night workers usually begin and close their work at relatively earlier hours in the evening and morning than corresponding day workers in the morning and afternoon, respectively, and they have, therefore, correspondingly more time before luncheon, after completing their sleep, than day workers have before breakfast. Hence, they can very well use the ordinary luncheon and dinner and take a light supper toward the close of the night's work.

In ordinary climates, free from miasmatic infections - which probably mean diseases borne largely by nocturnal insects - the prejudice against night air is mainly imaginary; indeed, it is claimed by some that direct sunlight is deleterious to all organisms and that its hygienic value is limited entirely to its germicide action. Thus, if sleep and food are regularly taken, there is no marked hygienic disadvantage about night work.

A full stomach is commonly regarded as a protection against prolonged physical and mental fatigue, exposure to cold, damp, and infection. This is true in the sense that the increased demand for nutriment should be met by hearty meals, even at un-usual hours; but it is a dangerous fallacy, if construed as an indication for overeating or for eating at too short intervals. Coffee, tea and chocolate have their greatest value and alcoholic beverages their greatest danger, in meeting such emergencies. In particular, alcohol should not be used before going out into the cold.