TOXICOLOGY, the study of poisons. The word poison is difficult to define, since many substances which in minute amounts exercise no harmful action on the body may in large quantities produce disastrous effects. Then again, some substances which are harmless when taken into the stomach, as water, for in stance, if injected into a blood-vessel prove very dangerous, causing death at times from the destructive action of the water on the blood-cells. Moreover, the many studies of recent years on bacteria and other low forms of life have resulted in a new series of concep tions regarding the poisonous actions of the compounds formed by these bodies; and still further, certain forms of perverted metabolism of the human body result in the production of certain products which, retained by the body, work harmful effects (See AUTOINTOXICA TION; METABOLISM). If all the different factors are taken into consideration, a strictly scientific definition of the word poison cannot be given. In general it is said that a poison is any sub stance which brings about a change in the molecular composition of an organ or organs, causing its functions to depart wry distinctly from the normal. But what grade of molecular disturbance is necessary to make a substance a poison, or how far from the normal must be the functional alteration, it is impossible to say. Many substances, strychnine for example, while being distinctly poisonous in appreciable doses, are very useful and helpful to the body when given in small amounts. Infinitesimal doses of copper salts act as pronounced poisons on cer tain forms of lowly organized plants, while a higher plant, the potato, does not suffer from large doses used as a spray to kill insect or fungus-parasites.
The modern conception of poisonous action is essentially a physicochemical one, the dis tinction between a molecular physical action and a molecular chemical action being difficult to make. But it is believed that for practically all forms of poisons a distinct alteration in the character of the cells of the body takes place, as well as a change in the chemical composition of the poisonous substance. It is impossible at
the present time to summarize these changes. It is rarely that the reaction between the body cell and the poison is purely of a physical nature, yet this very frequently happens in many poisons that act on the blood. By some of the poisons — the anilines, for example tire blood undergoes changes, not so much due to new chemical compounds formed, as to physical changes in the tension of the blood serum and the blood-corpuscles, whereby the blood-coloring matters stream out into the plasma, and the oxygen-carrying function of the blood is lost. Similar types of poisoning result from some of the metals, and the poison of the cholera organism is thought to act in a like manner. In other poisons there is a direct union of the ions of the poison with some constituents in the cells of the body, mak ing new chemical compounds, and thus inter fering with the molecular activities of the cells.
Von Jaksch has divided the poisons into two classes: the exogenous poisons, or those that come from without the body, and enter by way of the skin, the lungs, the stomach or the intestines; and the endogenous intoxications that result from changes within the human body through disordered metabolism. Oc casionally the former class may cause such changes in the body that death results from an intoxication of the second variety. Thus a severe irritant to the kidneys, such as canthar ides, may cause such an acute inflammation of that organ that it cannot secrete urine, and the patient may die of urwmic poisoning. In much the same manner certain bacteria find en trance into the body and develop poisons both within the tissues and also in the intestinal canal, and furthermore provoke putrefactive processes in the food the intestinal canal. This brings about a triple form of poisoning, as it were.