Venom, a kind of secretion produced in certain animal bodies, which acts as a poison when introduced into the tissues of other animals. The characteristics of a venom, as distinguished from poisons in general, are that it is of organic origin, produced in special secreting organs, termed "poison glands," and that it is introduced into the tissues by means of certain organs specially adapted for the purpose, which have the form of stings or fangs. Thus we have the venom of the rattlesnake, the viper, the scorpion, and the tarantula. A virus, on the other hand, though also a poison of an organic, and usually an animal origin, is the result of diseased action or of putrescence, and usually has the power of exciting in the poisoned individual the same disease as that by which it was itself produced. Thus we speak of the virus of smallpox, of cowpox, and the like. The poison of hydrophobia is properly not a venom but a virus, since it is due to the presence of a diseased element in the natural secretion of the saliva, and reproduces the same disease by inoculation. A virus does not usually cause any local irritation; or if so, as in the case of cowpox or smallpox, it is quite insignificant as compared with the effect upon the system at large.

A venom, on the other hand, generally produces great pain, swelling, and inflammation at the spot where it is applied; and its constitutional effect appears to be in great measure sympathetic with the local disturbance.