An abortion (an event or procedure that terminates or brings a pregnancy to an end) can be spontaneous (unplanned) or induced (planned). The spontaneous abortion of a fetus (name given to unborn young from the end of the eighth week of development to the moment of birth) is called a miscarriage, and occurs in about twenty-four percent of all pregnancies.


Acupuncture is an ancient method for relieving pain and treating disease using very fine metal needles. While the invention date of acupuncture is not known, the theory behind it has been handed down through the centuries.

Adhesives and Adhesive Tape

Adhesives are substances that hold the surfaces of materials together, often permanently. Natural adhesives (of plant or animal origin), synthetic (artificially produced) adhesives, and combinations of the two can be categorized according to whether they are activated by heat and whether they form rigid or stretchy bonds.

Adrenocorticotropic Hormone (ACTH)

Adrenocorticotropic hormone (also known as "ACTH") is a pituitary hormone. A hormone is a chemical produced by a gland.

Aerosol Spray

An aerosol is a gaseous suspension (hanging) into air of solid or liquid particles. The word "aerosol" also refers to the dispenser or package used to change the ingredient inside the container into an aerosol.

AIDS Therapies and Vaccines

There are several reasons why AIDS is difficult to treat. HIV is a retrovirus (a virus made up of ribonucleic acids, or RNA, instead of deoxyribonucleic acids, or DNA).

Alcohol, Distilled

Alcohol is perhaps the oldest drug used by humans. Alcohol affects the body according to its level of concentration in the blood, producing a feeling of well-being at the smallest blood alcohol concentration, to unsteadiness when walking, slurring of the speech, drowsiness, then inebriation (a drunken state) at higher levels.


The origin of the ambulance was tied to the needs of war. Battlefields were often miles from medical tents.


Amniocentesis is the process of removing a sample of amniotic fluid from the mother's uterus (a pear-shaped organ located in the pelvis where unborn young develop) in which the fetus (growing baby) floats. The fluid and fetal cells in the fluid are then analyzed to check for and diagnose possible genetic disorders.


Amputation is the surgical removal of all or part of an appendage (such as a leg or arm). Amputation has been practiced since earliest times, but usually out of desperation, as in the case of a crushed limb.


Anaphylaxis is a violent allergic reaction of the whole body which can result in death. During anaphylaxis, the allergic person's throat swells so much that she or he cannot breath, while internal organs may start to shutdown.


Anesthetics are substances administered to deaden pain or produce a state of anesthesia (a condition in which some or all of the senses, especially touch, stop functioning or are reduced). Early Chinese practitioners used acupuncture (the insertion of thin, solid needles into specific locations on the body) and the smoke of Indian hemp (a tough fiber obtained from the stems of a tall plant) to dull a person's awareness of pain.

Angiography, Cerebral

Wilhelm Konrad Roentgen's (1845-1923; German physicist and winner of the first Nobel Prize for physics in 1901) discovery of X-rays in 1895 revolutionized most fields of science, including medicine. The fact that some parts of the body are more dense than others means that X-rays can be used to diagnose some medical problems.

Angiography, Coronary

Coronary angiography is an X-ray of the heart and blood vessels of a living patient. The X-ray is taken with a moving camera, which produces a very detailed and accurate picture of the condition of the coronary arteries.

Angioplasty, Balloon

Balloon angioplasty is a medical technique used to widen coronary (heart) arteries that have been narrowed by plaque (fatty material) deposits that cling to the inside of the artery walls. In a coronary (heart) disease called atherosclerosis ("hardening of the arteries"), the arteries become so dangerously clogged that surgery is required to clear the blockage.


Antabuse, also known by its scientific name disulfiram, medication was approved by the U.S. Food and Drug Administration (USDA) in 1951 for the treatment of alcoholism.


Antibiotics are medications taken to fight infections caused by bacteria. When they first became available during World War II (1939-1945), antibiotics were called "wonder drugs" because of their stunning record for safety and effectiveness.


Anticoagulants are substances that inhibit coagulation (clotting) of the blood. They are used to keep stored blood for transfusions from clotting, to treat conditions involving dangerous blood clotting (includings strokes and heart disease), and in situations where there is a serious risk of dangerous clotting, such as during certain surgical procedures.


Antihistamines are drugs used to relieve the symptoms of allergies caused by histamine, an organic (natural, basic) compound made from the amino acid histidine. Histamine is released from certain cells when the body is irritated by outside substances, such as pollen, or if the body thinks that a certain food is an enemy rather than a friend.


Antisepsis is the destruction or inhibition of (slowing the growth of) microorganisms (very small living substances invisible without a microscope) that exist on living tissue. Antiseptics are the substances that kill or prevent the growth of the microorganisms.