Humans live in a world where many other living things compete for food and places to breed

. The pathogenic organisms, ,or pathogens, are often broadly called germs, which cause many diseases to be able to invade the human body and use its cells and flu- ids for their own needs. (46)

Pathogenic organisms can enter the body in various ways. Some —such as those that cause the common cold, pneumonia, and tuberculosis—are breathed in. (47) Still others—such as those that cause bacillary dysentery, cholera, and typhoid fever— get in the body through contaminated food, water, or utensils.

Insects can spread disease by acting as vectors, or carriers. . (48) Germs may also enter the body through the bite of a mosquito, louse, or other insect vector. Kinds of disease

Infectious, or communicable, diseases are those that can be passed between persons such as by means of airborne droplets from a cough or sneeze. Tiny organisms such as bacteria and fungi can produce infectious diseases. So can viruses. So can tiny worms. Whatever the causative agent might be, it survives in the person it infects and is passed on to another. Or, its eggs are passed on. . (49)

The asymptomatic carrier can then pass the disease on to someone else without even knowing he has it.

Noninfectious, or noncommunicable, diseases are caused by malfunctions of the body. These include organ or tissue degeneration, erratic cell growth, and faulty blood formation and flow. Also included are disturbances of the stomach and intestine, the endocrine system, and the urinary and reproductive systems. Some diseases can be caused by diet deficiencies, lapses in the body's defense system, or a poorly operating nervous system.

. (50) These ailments include drug addiction, obesity, malnutrition, and pollution-caused health problems.

A. A disease is a condition that impairs the proper function of the body.

B. Ordinarily, the body's defense system can ward off these invaders.

C. Disability and illnesses can also be provoked by psychological and social factors.

D. Sometimes, a disease-producing organism gets into a person who shows no symptoms of the disease.

E. Others—such as those that cause venereal diseases—enter through sexual contact of human bodies.

F. Flies can carry germs from human waste or other tainted materials to food and beverages.

(46)