Food sanitation is now a subject of the highest importance. Either because of their source or condition, human foods may be the direct cause of disease, sometimes because they communicate to the human subject pathogenic germ life, and sometimes because of the physiological effect of compounds that they contain naturally, or that have developed in them by holding them under undesirable conditions. With the changes in commercial conditions caused by the increasing spread and density of our population, the defense of the public against dangerous food materials has become an exceedingly complex and difficult matter.

There are several reasons for this, among which are the following:

1. The collection of raw food materials over wide areas from sources it is not easy to supervise or even know much about.

2. The transportation of foods over long distances, with the attendant danger of fermentative changes and contamination.

3. The exposure of foods to dust and flies, especially in city markets.

4. The storage of foods during long periods of time with consequent changes in their composition.

5. The introduction into foods, especially meats and canned goods, of compounds known as preservatives, that, when introduced into the digestive tract, may be deleterious to health.

In order to control these conditions, national, state, and municipal regulations have been adopted which have done much to improve the quality and healthfulness of commercial human foods. Such control is more or less imperfect, however. The best defense against unhealthful foods is such an understanding on the part of the purchaser of the sources of danger as to permit a wise discrimination in the selection of foods and in the conditions to which they are submitted.