Radiotherapy is the treatment of disease with radiation. Doctors use radiotherapy most often to treat certain kinds of cancers.


Retinography is a sophisticated means for identifying people by the pattern of blood vessels on the retina (the innermost coat of the back part of the eye). It requires the use of a special scanner about the size of a shoe-box that can map the unique pattern of blood vessels on the retina.

Rh Factor

Rh factor is also called "Rhesus factor" because it was first discovered in the blood of Rhesus monkeys (small monkeys from India often used for experimentation). Rh factor is an antigen, a substance which stimulates the production of antibodies to fight foreign invaders, such as viruses, bacteria and transplanted organs.


RU 486, also known as the "abortion pill," is considered one of the most controversial medical breakthroughs of recent times. (Abortion is the termination of a pregnancy and expulsion of the embryo or fetus from the uterus.) The pill was developed by French biochemist Etienne-Emile Baulieu (1926-).

Schick Test

During the late 1800s, a diphtheria epidemic killed thousands of children in western Europe and the United States and spurred research into ways of controlling the disease. Diphtheria is a contagious disease caused by a bacterium.

Separation of Siamese Twins

Siamese twins are identical twins who are physically joined together at some part of the body. Siamese twins result when the zygote (a fertilized ovum) undergoes incomplete separation.

Sex Hormones

Sex hormones are steroids (fat soluble compounds) that control sexual maturity and reproduction. These hormones are produced mainly by the endocrine glands.

Skin Grafts

Skin grafts have been performed for a long time. In the sixth century B.C., doctors in India were successfully performing skin grafts.


People usually think of steroids as drugs that athletes take to build their bodies more quickly. Steroids are more than that.


The stethoscope is an instrument for listening to sounds produced by organs in the human body, including the heart and lungs. One end of the stethoscope is placed against the body, and the other end is placed in or at the ear, a method called direct auscultation.


The discovery of streptomycin by microbiologist Selman Abraham Waksman (1888-1973; winner of the 1952 Nobel Prize in medicine) occurred in the mid-1940s. The discovery of this effective and safe antibiotic led to the taming of tuberculosis, or "TB." Streptomycin has also been found effective in treating several other infectious diseases.


The plant source of alkaloid strychnine was discovered in 1818. This discovery was made by French chemists Joseph-Bienaime Caventou (1795-1877) and Pierre-Joseph Pelletier.

Subzonal Injection

Subzonal injection is a method of in vitro fertilization. In this procedure, a drop of fluid containing sperm is placed under a microscope.

Sulfonamide Drugs

The sulfonamides, also known as sulfa drugs, halt the growth of bacteria. Their discovery paved the way for cheap and effective treatment of often fatal infections, including certain types of pneumonia.

Surgical Instruments

Surgery has been performed since ancient times. The earliest recorded surgical operations were circumcision and trepanation.

Syphilis Test

Syphilis was once a disease of epidemic proportions. Today, it is effectively treated with penicillin and other antibiotics.


The syringe is a pump-like device used to inject or remove liquids by suction. It consists of a tube that is tapered at one end and has a plunger at the other end.


In the earliest days of the medical profession, no device existed to measure a patient's body temperature. Evaluating a patients' body temperature depended totally on the doctor's personal methods of observation.


Like all the water-soluble B vitamins, thiamine functions as a coenzyme. Thiamine works primarily in the metabolism (processing) of carbohydrates, fats and proteins.


Thyroxine is the principal hormone produced by the thyroid gland. It promotes protein synthesis (blending) and growth, and also helps regulate the body's metabolism.