Hormone, HAWR mohn, is any of a number of chemical substances produced within an animal or a plant. A hormone is produced in one part of an organism, but it causes an effect in a different part. Thus, hormones serve as a means of communication among various parts of an organism. They act as "chemical messengers" that help these parts function in a coordinated way.
The word hormone comes from a Greek word that means to set in motion. In human beings and other animals, hormones control such body activities as growth, development, and reproduction. In plants, hormones regulate many aspects of growth. If an organism fails to produce the proper kind or amount of hormones, serious disturbances--or even death--may result. For example, giants and dwarfs--among both animals and plants--can result from faulty hormone production.
In 1902, scientists found the first definite evidence of the existence of hormones. That year, British researchers discovered that a chemical substance controlled certain activities involved in digestion. Since then, scientists have identified more than 30 hormones produced by the human body. They also have developed ways of extracting hormones from living tissue and techniques for manufacturing them in the laboratory.
