How foods are grown, handled, kept, prepared, used, served, affect human activity, health, growth. Different foods need different conditions. But all need special care in production and preservation until used. All require complete cleanliness as kept and handled from garden to table.

A market that looks and is clean at all times is essential for health. Protection of food from dust of streets, from refuse of all kinds, from insects (as flies and ants), from vermin (as mice and rats), and from diseased persons on farm, in market, at home, is a health-necessity. Dust, refuse, insects, vermin, ill persons, are disease-carriers.

Exposure to disease usually weakens general health even when it does not cause definite disease. Resisting disease-influences requires of the body unnecessary effort. This is added to that of living and working. Contaminated food has been in contact with disease-sources; it is one of the greatest dangers to life. Unsound food is food that is itself in unwholesome condition; it is a health-menace. Food is eaten to sustain life and promote living-activity. Its condition needs to be such that it can be a health-help, a strength-promoter, an energy-giver, and in childhood and youth also a growth-aid.

Fresh, sound food, free itself from contamination, must be kept apart from all that is not. Any moldy bread or fruit makes all near it unsafe, as does also all food-waste or waste products of living (as sewage) or of industry (as factory-refuse). Receptacles, wrappers, carts, cars, all need to be clean and thoroughly aired. House, shop, factory refrigerators, utensils, elevators, must likewise be well-aired and cleaned. Hands too need to be clean; all that handle food as produced, prepared, or eaten. Lack of cleanliness invites illness; unsound food undermines health; contaminated food causes disease.