od determines only the nutrients, as protein, carbohydrates, and fats;
and unless there is reason to believe the food contains injurious
substances no special tests for these are made. There are a number of
poisonous compounds that foods may contain, and many of them can but
imperfectly be determined by chemical analysis. Numerous organic
compounds are produced in foods as the result of the workings of
microoerganisms; some of these are poisonous, while others impart only
special characteristics, as taste and odor. The poisonous bacteria
finding their way into food produce organic compounds of a toxic
character; and hence it is that the sanitary condition of a food, as
influenced by preparation and storage, is often of more vital importance
than the nutrient content.[95]

[Illustration: FIG. 65.--TUBERCULOSIS BACILLI. (After CONN.)

Often present in dust particles and contaminated foods.]

280. Sources of Contamination of Food.--As a rule, too little
attention is given to the sanitary handling and preparation of foods.
They are often exposed to impure air and to the dust and filth from
unclean streets and surroundings, and as a result they become inoculated
with bacteria, which are often the disease-producing kind. Gelatine
plates exposed by bacteriologists under the same conditions as foods
develop large numbers of injurious microoerganisms. In order to avoid
contamination in the handling of food, there must be: (1) protection
from impure air and dust; (2) storage in clean, sanitary, and ventilated
storerooms and warehouses; (3) storage of perishable foods at a low
temperature so as to retard fermentation changes; and (4) workmen free
from contagious diseases in all occupations pertaining to the
preparation of foods. Ordinarily, foods should not be stored in the
paper wrappers in which they are purchased, as unclean paper is often a
source of contamination.

281. Sanitary Inspection of Food.--During recent years some state and
city boards of health have introduced sanitary inspection of foods, with
a view of preventing contamination during manufacture and
transportation, and this has done much to improve the quality and
wholesomeness. Putrid meats, fish, and vegetables are not allowed to be
sold, and foods are required to be handled and stored in a sanitary way.
Next to a pure water supply, there is no factor that so greatly
influences for good the health of a community as the sanitary condition
of the food. While