A great number of drugs which are employed in medicine, and are most useful when given in small doses, act as irritant poisons in large ones. Their action is then not restricted to the stomach, nor even to the whole of the intestinal canal, but they exercise, in addition, a marked effect upon other functions of the body, such as respiration and circulation.

In considering the physiological action of many drugs it is necessary to describe the effect they will produce when given in large quantities, as, for example, in an overdose, as well as in moderate or small ones.

It will save both time and space to consider here the action of irritant poisons generally, and to refer to this description when discussing the effect of individual drugs.

1 Lancet, April 21, 1883.

The symptoms of irritant poisoning are to a great extent the same, whatever be the irritants swallowed; it is therefore convenient to give an account of these symptoms, and then to mention the special peculiarities which occur in the case of different poisons.

A poison is most usually swallowed, and it then comes successively in contact with the lips, mouth and tongue, gullet and stomach. It may sometimes reach no farther, being either evacuated by vomiting or absorbed. It frequently, however, also passes into the intestine. On all those parts which it reaches it exerts a local action; besides this, however, it exerts a reflex action on the respiration and circulation. Corrosive poisons produce a feeling of burning in the lips, mouth, gullet, and stomach; the pain in the stomach, extending more or less over the abdomen, is accompanied by tenderness, and is increased by pressure. It is thus distinguished from the pain of colic, which is usually relieved by pressure.

The irritation of the stomach gives rise to vomiting; the vomited matters usually consisting, first of the contents of the stomach, next of bile or mucus, and lastly of mucus stained with blood. These matters may sometimes be more or less acted upon by the poison, where this is a strong acid or alkali. The intense irritation in the stomach produces effects on the respiration and circulation very much like those caused by a severe blow in the epigastrium. The heart's action is greatly weakened at first, and it may be rendered slow from reflex irritation of the vagus, but in the later stages it is generally rapid, very small, weak, or almost imperceptible; sometimes it may be intermittent (see Fig. 141). On account of the weakness of the circulation the face and the general surface of the body are pale, the cheeks sunken, and the extremities cold. The frequency of the respiration may vary, may be either slower or quicker than normal, but it is almost always laboured and shallow, as the intense irritation in the stomach renders the descent of the diaphragm in deep inspiration painful, and the sufferer therefore tries to avoid it.

Fig. 141.   Diagram to show the nervous mechanism by which the action of the heart may be depressed by irritation of the stomach. The reflex irritation of the vagus may render the heart's action simply weak, or slow and weak (vide p.

Fig. 141. - Diagram to show the nervous mechanism by which the action of the heart may be depressed by irritation of the stomach. The reflex irritation of the vagus may render the heart's action simply weak, or slow and weak (vide p. 310).

Although the pulse at the beginning of the poisoning may be slow, when advanced it is usually, as already mentioned, very rapid. Exceptions to this rule may occur, chiefly in the case of poisons which, after their absorption, have an action on the heart itself; these are potassium nitrate and salts of barium. In consequence of the weakness of the circulation the face is usually very pale, but an exception to this may occur in poisoning by corrosive sublimate, where the face may be flushed. In arsenical poisoning the face is not only pale, but assumes a bluish hue, and the pinching may be extreme, so that the condition resembles that of a person suffering from Asiatic cholera.

Where the poison is exceedingly corrosive, as in the case of acids and caustic alkalies, its local action on the stomach in causing swelling of the mucous membrane may tend partially to occlude the pylorus, and the greater part of the poison may either remain in the stomach itself or be ejected by vomiting without passing into the intestine. In such cases vomiting will occur alone without being accompanied by purging, and the pain in the abdomen may be less diffused. Most irritant poisons, however, pass from the stomach into the intestines, and thus violent purging is induced in addition to the vomiting. The inflammation of the intestines also causes the pain to be diffused over the whole abdomen.

Peculiarities in the Action of different Irritant Poisons. - Acids throw down albumen as a white precipitate, and in consequence, when brought in contact with the lips or tongue in a concentrated condition, they cause white stains. The white stain is most marked in the case of carbolic acid; it occurs also from hydrochloric acid; it may occur from sulphuric, but as the further action of the sulphuric is to char albumen or other organic substances, the stain may acquire a brown or black colour. Nitric acid produces a yellow stain, rendered brighter by the application of ammonia. Perchloride of iron produces a yellowish-brown stain; the caustic alkalies remove the epidermis and give a soapy feeling to the surface, but do not leave any stain. After a short time the mucous membrane becomes injected and swollen from the irritation.

In the mouth the taste peculiar to the poison often leads to its detection, so that very little of it may be swallowed in cases where a person was about to take it unwittingly. Arsenic, although a powerful irritant in the stomach, is almost tasteless.

As the poison passes down the gullet, it may have an important influence on the respiratory tract; this is especially the case where it gives off fumes like nitric acid, hydrochloric acid, and ammonia; the fumes, passing into the larynx and trachea, excite irritation, spasm, and inflammation, and may cause death by suffocation. Death by suffocation may, however, sometimes occur from the action of poisons which do not fume, e.g. sulphuric acid; the local irritation producing such great oedema and reflex spasm about the epiglottis as to cause obstruction to the respiratory passages. Sometimes, also, such poisons as sulphuric acid may pass directly into the trachea instead of the oesophagus, and thus cause very rapid death from suffocation.

Purging is usually absent and the bowels constipated in poisoning by strong alkalies or acids, and by salts of lead; the former probably act by corroding the stomach, and partially occluding the pylorus; the latter by lessening the peristaltic movements of the intestine. In the case of lead salts the abdominal pain differs from that of ordinary irritant poisons, being of a colicky nature, and to a certain extent relieved by pressure.

Secondary Effects of Irritant Poisoning. - After the immediate condition of collapse caused by the powerful action of the irritant has passed off, the local inflammation which it has produced may give rise to a general febrile condition, with hot skin, flushed face, and quick bounding pulse. This condition may be accompanied by other symptoms due to the physiological action of the poison after its absorption; thus in the case of corrosive sublimate, there may be the metallic taste, sore gums, and profuse salivation characteristic of mercurial poisoning.

One of the most important instances of the secondary effects of irritant poisons is phosphorus; after the primary symptoms of gastric irritation have passed off the patient may appear perfectly well, and then vomiting and purging may set in a second time. These are due, not to the local action of the phosphorus which has been swallowed on the stomach and intestines, but to the changes in the liver, blood, and other organs, which the phosphorus has produced after its absorption. A similar condition has been observed in poisoning by arsenic, but usually the symptoms of arsenical poisoning are continuous, and do not exhibit a distinct intermission of this kind.

Death may occur from the secondary action of some poisons a good while after the primary symptoms have disappeared; thus strong acids and alkalies may produce death, weeks or even months after they have been swallowed, from the effects of their local action on the oesophagus or the stomach. During the passage down the oesophagus they may destroy the mucous membrane to such an extent that when it heals and the cicatrix begins to contract, the lumen of the tube may be completely obstructed, so that no food can reach the stomach, and the patient dies of starvation; or the mucous membrane of the stomach may be destroyed to such an extent that what remains is insufficient to digest the food, and the patient dies from non-assimilation.