(b) Bacilli. Bacilli are rodshaped; however they vary from straight to
irregularcurved and branchedshapes. They cause such common diseases as typhoid
fever, diphtheria, tuberculosis, and leprosy.
(c) Spirochetes. Spirochetes are spiralshaped and can move or twist.
Spirilla and Treponema pallidum are examples. The latter causes syphilis.
(4) Fungi. These extracellular endoparasites or ectoparasites are larger
and higher in the scale of plant life than are the bacteria. They include the yeasts and
molds, and produce infections of the skin such as ringworm, and infections of the
mucous membranes such as thrush. Some attack internal organs, especially the lungs
and central nervous system, very often with disastrous results.
(5) Protozoa. These are onecelled animal parasites (either extracellular or
intracellular) that cause such common diseases as malaria and amoebic dysentery.
(6) Metazoa. These manycelled, larger animals include the helminths
(worms) such as the ascaris, the hookworm, the pinworm, the tapeworms, and the
flukes, as well as the arthropods (mites, lice, and so forth).
c. Intoxicants. Taking into the body any chemical substance that causes
disease or injury is known as intoxication. Many substances are very useful in small
amounts, and do not cause intoxication, but the same substances may be very toxic in
larger amounts, and result in severe illness or death.
d. Trauma. Trauma may be defined as injury sustained by the body as the
result of a physical agent or force. The physical agents that may produce trauma or
injury of the body are:
Light. In excessive amounts, light can cause temporary blindness.
(2) Heat. Excessive heat can cause burns of the body, heat cramps, heat
(3) Cold is absence or deficiency of heat. Exposure to low temperatures
can result in frostbite and other cold injury.
Electricity. One can sustain burns, electric shock, or both when exposed
to this agent.
(5) Ionizing radiation. Excessive exposure to xrays or to radio active
elements can produce burns, radiation sickness, malignancies, cataracts
of the eye, and genetic changes.
(6) Mechanical forces. These agents produce contusions (bruises),
abrasions (scrapes), lacerations (cuts), fractures, sprains, and strains.