Carrie MacDougall, age 11, of Annapolis, Md., for her question:

WHAT IS A TOXIN?.

A toxin is a poison produced by a living organism. Toxins may cause many diseases and even death.

Toxins sometimes remain inside the organism and they cause poisoning only when the organism is broken up and the poison escapes. These are called endotoxins.

Other Toxins, called exotoxins, are secreted into the substance surrounding the organism.

Bacteria that infect the human body may produce toxins that cause such diseases as diphtheria, tetanus, gas gangrene and scarlet fever. Some bacteria and fungi secrete toxins into the foods in which they grow. A disease such as botulism may result if such food is eaten.

Doctors prescribe antitoxins to fight toxins. Antitoxins are serums or substances formed in the body to neutralize a toxin.

The venoms of poisonous snakes, spiders and insects are toxins.

Some tropical fish produce toxins that remain in their bodies. These toxins do not harm the fish but they can cause illness to a person who eats the fish.