Computerized Axial Tomography

A computerized axial tomography (CAT) scan is a special type of X-ray used for viewing the internal organs of patients. Although a regular chest X-ray can show the heart and lungs, the CAT scan can show the same organs but with detail 100 times greater and with little or no additional irradiation (exposure to radiation).

Contact Lens

A contact lens is a small, shell-shaped piece of eyeware used to correct vision. It is placed directly over the cornea (the transparent, or clear, tissue over the pupil and the iris, or colored part of the eye).


Cortisone is one of a family of steroid hormones secreted by the cortex (outer layer) of the adrenal gland, which is located on the kidneys. The adrenal cortex is the chief organ of homeostasis (the body's ability to remain internally stable even in the presence of stressful changes in the environment, such as extreme cold, hunger, thirst, and danger).


Cryogenics is the study and use of materials at extremely low temperatures. Such low temperatures cause changes in the physical properties of materials that allow them to be used in unusual engineering, industrial, and medical applications.


Curare is a name used to identify a variety of highly toxic (poisonous) extracts from some types of woody vines that grow in South America. European scientists began studying curare in the late sixteenth century after explorers learned that Indians living along the Amazon and Orinoco Rivers in South America had been using it for centuries to make poison-tipped hunting arrows.


Cyclosporine is a drug obtained from a type of soil fungus found in Norway called Tolypocladium inflatum. The drug is valuable in organ transplants because it suppresses the action of certain cells in the body's immune (disease-fighting) system that can reject the transplanted organ.


DDT (dichloro-diphenyl-trichloroethane) is perhaps the most recognized of all insecticides because it's use helped reveal the many hazards associated with synthetic (man-made) pesticides. This colorless, odorless, insoluble toxic pesticide contains up to fourteen chemical compounds.

Defibrillator and Cardioverter

Ventricular fibrillation occurs when the individual muscles of the heart contract in a random, uncoordinated way. The heart appears to shiver, and blood circulation ceases.

Dental Drill

When a tooth develops a cavity, the decayed tissue must be removed. The earliest devices for doing this were picks and enamel scissors.

Dental Fillings, Crowns, and Bridges

Cavities (areas of decay) in teeth have been filled since earliest times with a variety of materials, including stone chips, turpentine resin (an organic plant substance), gum, and metals. Giovanni d'Arcoli recommended gold-leaf (gold beaten into very thin sheets) fillings in 1484.


Deoxyribonuclease (pronounced "dee-oxy-rybo-noo-clee-ase"), or recombinant human deoxyribonuclease 1 (rhDNase or DNase), is an experimental drug used to treat cystic fibrosis (CF), an inherited lung disease. People with CF experience chronic (constant) and increasingly worse symptoms throughout their lives.

Dialysis Machine

Dialysis is the process of removing waste products from the blood. This removal is normally done by the kidneys, but if they are impaired (damaged), then a dialysis machine (also called an artificial kidney) can perform a similar function.

Dick Test

The Dick test is a laboratory test designed to indicate whether or not a person is immune to (will not get) scarlet fever. Scarlet fever is a childhood disease.


Doctors often treat illnesses with drugs derived (obtained) from special substances found in plants. One of the most important of these drugs is digitalis, which is used to treat congestive heart failure.

DPT Vaccine

The DPT vaccine is one type of preventive medicine called immunization (to make things resistant to disease). The vaccine causes the body to form protective antibodies (disease-fighting proteins) against three serious diseases: diphtheria, pertussis (whooping cough), and tetanus (lockjaw).

Electrocardiograph (ECG)

In the late 1700s medical researchers learned that muscular contractions produce tiny electric currents. Research scientists reasoned that a recording of the electric impulses of the heart could reveal irregularities and, hence, heart disease.

Electroencephalogram (EEG)

An electroencephalogram (EEG) is a graphic (vivid) picture of the electrical activity of the brain. An EEG is made by placing electrodes (small terminals which conduct an electrical current) on the subject's scalp and connecting the electrode wires to a machine known as an electroencephalograph.

Embryonic Transfer

Embryonic transfer is the moving of a fertilized egg that is between two and eight weeks old from the womb of one woman to the womb of another. The first successful human embryo transfer occurred in 1983.

Endorphin and Enkephalin

Endorphin and enkephalin are the body's natural painkillers. When a person is injured, pain impulses travel up the spinal cord to the brain.


An endoscope is an instrument that allows doctors to view the inner workings of the human body without having to perform surgery. Endoscopes are sometimes called fiberscopes.