during first aid treatment of snakebite is not ordinarily harmful, but snake venom injected parenterally is extremely poisonous.
There are various ways in which poisons may be introduced into the body, the most common being by mouth, inhalation, and injection. Poisons taken by mouth enter the circulation through absorption from the stomach and intestine. Those inhaled enter the circulation through the lungs. When parenterally injected or deposited into the urethra, rectum, or vagina, poisons enter the circulation through absorption from the body tissues in those areas. If the injection is intravenous, the poisons are directly introduced into the bloodstream. Poisons may also be introduced by application to open wounds and to the unbroken skin. After entering the circulation, a poison is carried by the blood to the tissues and organs susceptible to its action and attacks them.
Most of the excretion of poisons from the body occurs in the kidneys, liver, gastrointestinal tract, and skin. Poisons may be excreted from the system unchanged or in the form of other compounds into which they have been transformed by the action of various body organs and tissues. The most damaging effects of some poisons are found at the point of excretion.
Various conditions of the individual may modify the actions and effects of poisons on the body. The age of the victim makes a great deal of difference, with young children being more susceptible to poisons than adults. Conditions caused by poisons will vary because of a personal idiosyncrasy; that is to say, some persons by nature are unusually sensitive to certain poisons, while others possess a natural tolerance for certain poisons that is not the result of habitual use. Through habitual use of certain poisons, especially narcotics, most persons may become so accustomed to their effects that they are not poisoned when taking doses that would ordinarily prove lethal in the unaddicted. It occasionally happens, however, that continual external use of chemical substances results in hypersensitivity. The actions of poisons may be considerably modified by disease, some diseases increasing and others lessening the action of poisons. In the latter case, large doses are usually required to produce the desired effect.
Poisoning may either be acute or chronic. Acute poisoning is the condition brought on by taking an overdose. Chronic poisoning is the condition brought on by taking repeated doses of a poison or as the result of the absorption of the poison over a long period.
These poisons are present in the gaseous state and if inhaled, destroy the capability of the blood as a carrier of oxygen and irritate or destroy the tissues of the air passages and lungs. When in contact with the skin and mucous membranes, gaseous poisons produce lacrimation, vesication, inflammation, and congestion. Examples are carbon monoxide, carbon dioxide, hydrogen sulfide, sulfur dioxide, ammonia gas, chlorine gas, and chemical warfare agents
Inorganic poisons fall into two classes: (a) Corrosives, which are substances that rapidly destroy or decompose the body tissues at point of contact. Some examples are hydrochloric, nitric, and sulfuric acids; phenol; sodium hydroxide; and iodine. (b) Metals and their salts, which are corrosive and irritate locally, but whose chief action occurs after absorption when they damage internal organs, especially those of excretion. Some examples are arsenic, antimony, copper, iron, lead, mercury, radioactive substances, and tin.
These poisons are nitrogenous plant principles that produce their chief effect on some part of the central nervous system. Some examples are atropine, cocaine, morphine, and strychnine.
These poisons include various chemical compounds, some obtained from plants, having hypnotic, neurotic, and systemic effects. Some examples are barbiturates, salicylates, digoxin, and turpentine.
For convenience of study, the following general classification of poisons is based according to their effects on the body and the general symptoms of poisoning.