An antitoxin is an antibody capable of destroying a toxin made by microorganisms. An antitoxin provides passive immunity. For example, if a child gets whooping cough, an antitoxin prepared in horses against diphtheria may be useful in treatment. The antitoxin can only be of short-term value because the antibodies against diphtheria were made by the horse and the child is just the passive recipient of the antibodies. A ”toxin,“ in this sense, is one of a number of poisons produced by certain plants, animals, and bacteria usually referring to a particular protein produced by some higher plants, animals and pathogenic bacteria. A toxin typically has a high molecular weight (as compared to a simple chemical poison), is antigenic (elicits an antibody response), and is highly poisonous to living creatures.