In the context of biology, poisons are substances that can cause damage, illness, or death to organisms, usually by chemical reaction or other activity on the molecular scale, when a sufficient quantity is absorbed by an organism. Legally and in hazardous chemical labelling, poisons are especially toxic substances; less toxic substances are labelled "harmful", "irritant", or not labelled at all.
In medicine (particularly veterinary) and in zoology, a poison is often distinguished from a toxin and a venom. Toxins are poisons produced via some biological function in nature, and venoms are usually defined as biologic toxins that are injected by a bite or sting to cause their effect, while other poisons are generally defined as substances which are absorbed through epithelial linings such as the skin or gut.
Some poisons are also toxins, usually referring to naturally produced substances, such as the bacterial proteins that cause tetanus and botulism. A distinction between the two terms is not always observed, even among scientists.
Throughout human history, intentional application of poison has been used as a method of assassination, murder, suicide and execution. As a method of execution, poison has been ingested, as the ancient Athenians did (see Socrates), inhaled, as with carbon monoxide or hydrogen cyanide (see gas chamber), or injected (see lethal injection). Many languages describe lethal injection with their corresponding words for "poison shot". Poison's lethal effect can be combined with its allegedly magical powers; an example is the Chinese gu poison. Poison was also employed in gunpowder warfare. For example, the 14th century Chinese text of the Huo Long Jing written by Jiao Yu outlined the use of a poisonous gunpowder mixture to fill cast iron grenade bombs.
On the whole, however, poisons are usually not used for their toxicity, but may be used for their other properties. The property of toxicity itself has limited applications: mainly for controlling pests and weeds, cleaning and maintenance, and for preserving building materials and food stuffs. Where possible, specific agents which are less poisonous to humans have come to be preferred, but exceptions such as phosphine continue in use.
Most poisonous materials still in use are used for their chemical or physical properties other than being poisonous. Many over-the-counter medications, such as aspirin and Tylenol, are quite toxic if ingested in sufficiently large quantities. Even alcohol can become toxic if too much is ingested in a short enough time. In laboratory environments, where specific chemical properties are often required, the most effective, easiest, safest, or cheapest option for use in a chemical synthesis may be a poisonous material. If a toxic substance possesses these properties more exactly than a non-toxic one, the toxic substance is superior. Chromic acid is an example of such a "simple to use" reagent, but reactivity, in particular, is important. Hydrogen fluoride (HF), for example, is both poisonous and extremely corrosive. However, it has a high affinity (free energy) for silicon, which is exploited by using HF to etch glass or to manufacture silicon semiconductor chips.
On the other hand, certain medical treatments actually make deliberate use of the toxicity of certain substances. Antibiotics (originally harvested from organisms but now artificially produced in laboratories) are highly disruptive to the biochemistry of micro-organisms while having almost no direct effect upon humans. Similarly, the drugs used in chemotherapy are quite toxic; the reason chemotheraputic drugs have far more severe side effects than antibiotics is that their toxicity is not as narrowly tailored. Their benefit arises from the fact that they are—hopefully—more toxic to cancerous cells than normal ones. Such substances could be classified as poisons under the categories defined above, as they are generally artificial in nature, but are not generally discussed as such.
Venom is any of a variety of toxins used by certain types of animals, for the purpose of defense and hunting. Generally, venom is injected by such means as a bite or a sting, while a poison is absorbed by ingestion or through the skin.
There is a difference between organisms that are venomous and those that are poisonous, two commonly confused terms applied to plant and animal life. Venomous, as stated above, refers to animals that deliver (often, inject) venom into their prey when hunting or as a defense mechanism. Poisonous, on the other hand, describes plants or animals that are harmful when consumed or touched. A poison tends to be distributed over a large part of the body of the organism producing it, while venom is typically produced in organs specialized for the purpose. One species of bird, the hooded pitohui, although not venomous, is poisonous, secreting a neurotoxin onto its skin and feathers. The slow loris, a primate, blurs the boundary between poisonous and venomous. From patches on the inside of its elbows it secretes a toxin, which it is believed to smear on its young to prevent them from being eaten; however, it will also lick these patches, giving it a venomous bite.
Snake venom is produced by glands below the eye and delivered to the victim through tubular or channeled fangs. Snake venoms contain a variety of peptide toxins (Proteases), which hydrolize protein peptide bonds, and nucleases, which hydrolize the phosphodiester bonds of DNA. Snakes use their venom principally for hunting, though the threat of being bitten serves also as a defense. Snake bites cause a variety of symptoms including pain, swelling, tissue damage, low blood pressure, convulsions, and hemorrhaging (varying by species of snake).
Human immunity against snake venoms is one of the oldest forms of vaccinology to date (about AD 60, Psylli Tribe). Since then many humans and tribes have attempted to immunize with snake venom to achieve immunity(Bill Haast, Charles Tanner,Joel La Rocque, Harold Mierkey, Herschel Flowers, Ray Hunter, Tim Friede, Burma Toxoid Project, Habu Toxoid Project, Pakokku Snake Clan, Wanyamwesi Tribe, Dr. Eizenberger). Charles Tanner and Herschel Flowers were studied with dried snake venom and achieved strong immunity(1).Joel La Rocque self injected Eastern diamondback venom and developed a high IgG neutralizing antibody for several rattlesnake species.Harold Mierkey has done so for years. Tim Friede was studied twice with a self-directed vaccine experiment using pure venom and achieved very high IgG neutralizing antibodies with mamba and cobra venom(1). The present goal is to develop a DNA-based vaccine for the Old World using the genes that encode the venom with an electroporation device for DNA delivery(1). If successful, some of the over 100,000 people that die from snakebite in the Old World will be saved. (1,2) http://dnavaccine.com/modules.php?name=News&file=article&sid=1413. Friede, Tim. Venomous Snake Vaccinology, 5th World Congress of Herpetology in Africa.
Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License)