mechanisms play an important role in preventing pulmonary effects from inhalation of
dusts, fumes, and other forms of potentially hazardous materials.
b. The Skin Surface. The skin, with its thick layers of cells and its secretions, is
almost impervious to chemical agents. However, certain chemicals, such as solvents
and gases, can penetrate the skin's barriers.
c. The Excretory System. The body attempts to modify harmful substances
into less harmful substances. The liver and kidneys play a major role by extracting and
expelling chemicals. However, the excretory system is perhaps the least effective of the
body's defenses against harmful chemicals.
EFFECTS OF CHEMICALS ON THE BODY
Many chemicals may act as toxic agents. A detailed discussion of all the
biological actions of all the toxic agents a preventive medicine specialist would
encounter would be an impossible undertaking. Instead, the toxic agents will be
discussed according to their general biological actions.
a. Irritants. The basis of classifying these materials is their ability to cause
inflammation of mucous membranes. Many irritants are strong acids and alkalis familiar
as corrosive to nonliving things. Bear in mind that inflammation is the reaction of living
tissue and is distinct from chemical corrosion.
b. Asphyxiates. The basis of classifying these materials is their ability to
deprive the tissue of oxygen. The materials classified as asphyxiates do not damage
the lungs. Simple asphyxiates are physiologically inert gases that act when they are
present in sufficient quantities to exclude an adequate oxygen supply. Among these
substances are nitrogen, nitrous oxide, carbon dioxide, hydrogen, helium, methane, and
ethane. Some of these gases are chemically reactive and some may pose a major
threat of fire. Chemical asphyxiates are materials which specifically render the body
incapable of utilizing an adequate oxygen supply. Two classic examples are carbon
monoxide and cyanides.
c. Anesthetics. The main action of these materials is their depressant effect
upon the central nervous system, particularly the brain. The degree of anesthetic action
depends upon the effective concentration in the brain as well as upon the specific
pharmacological action. The anesthetic potency of simple alcohol rises with increasing
numbers of carbon atoms up to amyl alcohol, which is the most powerful of the series.
d. Lung Damaging Agents. In this category are materials that produce
damage of the pulmonary tissue but not by immediate irritant action. Materials such as
free silica produce fibrotic changes. Asbestos also produces a typical damage to the
lung tissue, and there is newly aroused interest in possible effects of low-level exposure
of individuals who are not asbestos workers. Other dusts, such as coal dust, can