Action of Poisons.— Poisons may exert a twofold action. This may be either local, or remote, or both local and remote. The local action of a poison is usually one of corrosion, inflammation, or a direct effect upon the sensory or motor nerves. The remote actions of poisons are usually of a specific character, though some writers group the remote effects of poisons under two heads, and speak of the common and the specific remote effects of a poison. The local action of a poison of the corrosive class is usually so well marked and obvious that the fact of the administration of a poison of this class is generally unmistakable. The same may be said, in a less degree, of the irritant poisons, especially the mineral irritants; but here the symptoms sometimes so closely simulate those of natural disease as to render the recognition of the administration of poison a matter of difficulty. Hence an accurate acquaintance with the remote specific effects of the various poisons is indispensable to the medical jurist. The class of poisons which has been administered or taken will thus be suggested to his mind by the observation of the symptoms; and not unfrequently the specific poison taken will be suspected. It is almost universally admitted that absorption of a poison is necessary for the production of its specific remote effects, and the old notion that a poison may kill, by its action through the nervous system, without absorption, is abandoned.

Modifying Circumstances.— The ordinary action of a poison may be greatly modified by the largeness of the dose, by the state of aggregation, admixture, or of chemical combination of the poison, by the part or membrane to which it is applied, and by the condition of the patient. Thus, for example, opium may be a medicine or a poison according to the dose in which it is given; and a dose of the drug which may be beneficial to an adult in certain states of the system may be fatal to a child, or to an adult when suffering from some forms of disease. All barium salts, again, are poisonous, except the quite insoluble sulphate. The simple cyanides, and many double cyanides, are highly poisonous; but yellow prussiate of potash, which is a double cyanide of iron and potassium, is almost without action upon the system. The part or tissue to which a poison is applied greatly affects the activity of a poison, owing to the varying rapidity with which absorption takes place through the cutaneous, mucous, and serous surfaces, and by the other tissues of the body. Curare, an arrow poison, may be swallowed in considerable quantity without appreciable result, whilst a minute quantity of the same substance introduced into a wound is speedily fatal. Idiosyncracy has an important bearing in toxicology. Pork, mutton, certain kinds of fish, more especially shell fish so-called, and mushrooms have each produced all the symptoms of violent irritant poisoning, whilst other persons who have partaken of the same food at the same time have experienced no ill effects. Some persons are stated, on good authority, to be capable of taking with impunity such poisons as opium, corrosive sublimate, or arsenic, in enormous doses,—and this irrespective of habit, which is known to have such an influence in modifying the effects of some poisons, notably the narcotics. A tolerance of poisons is sometimes engendered by disease, so that a poison may fail to produce its customary effect. Thus, opium is tolerated in large quantities in tetanus, and in delirium tremens; and mercurial compounds may in some febrile affections fail to produce the usual constitutional effects of the metal. On the other hand, diseases which impede the elimination of a poison may intensify its effects.

The evidence that a poison has been administered is based upon the symptoms produced, on the appearances met with in the body after death, on the analysis of articles of food and drink, of excreta and ejecta, and of the organs of the body after death, and on physiological experiments made with substances extracted from the same articles. These physiological experiments are usually made upon animals, but in some cases, as for instance when aconite has to be searched for, the physiological experiments must be made also upon the human subject. The evidence obtained from one or more of these sources, as compared with the properties or effects of various known poisons, will enable the medical jurist to form an opinion as to the administration or non-administration of a poison.

The symptoms exhibited by the patient during life rarely fail to afford some clue to the poison taken. Persons may, however, be found dead of whose history nothing can be learned. Here post-mortem appearances, chemical analysis, and, it may be, physiological experiments are all-important for the elucidation of the nature of the case.

Poisoning may be acute or chronic. The general conditions which should arouse a suspicion of acute poisoning are the sudden onset of serious and increasingly alarming symptoms in a person previously in good health, especially if there be pain in the region of the stomach, or, where there is complete prostration of the vital powers, a cadaveric aspect, and speedy death. In all such cases the aid of the analytical chemist must be called in either to confirm well-founded or to rebut ill-founded suspicions.

The mode of treatment to be adopted in the case of poisoned persons varies greatly according to the nature of the poison. The first indication, when the poison has been swallowed, is to evacuate the stomach; and this may usually be done by means of the stomach-pump when the poison is not of the corrosive class; or the stomach may be gently washed out by means of a funnel and flexible siphon-tube. In many cases emetics are valuable. Antidotes and counter-poisons may then be given. The former are such substances as chalk to neutralize the mineral acids and oxalic acid; the latter have a physiological counteraction, and are such as atropine, which is a counter-poison to morphia. These may usually be administered most effectively by hypodermic injection. The stomach may to a certain degree be protected from the injurious effects of irritants by the administration of mucilaginous drinks; alkaloids may be rendered sparingly soluble by means of astringent substances containing tannin; and pain may be relieved by means of opium, unless contra-indicated by the nature of the poison. The effects of the convulsant poisons, such as strychnine, may be combated by means of the inhalation of chloroform.

The classification of poisons is a matter of difficulty. Various attempts have been made to classify them scientifically, but with no signal success; and perhaps the best system is that which groups the various poisons according to the more obvious symptoms which they produce. Our knowledge of the more intimate action of poisons is still too imperfect to admit of any useful classification according to the manner in which they specifically affect the vital organs. Poisons may in the manner indicated be classified as (1) Corrosives, (2) Irritants, (3) Neurotics, and (4) Gaseous Poisons. The subject of poisonous food has already been treated under the heading Medical Jurisprudence (vol. XV. pp. 781-2).

1. Corrosives.

The typical member of this class is corrosive sublimate, the soluble chloride of mercury. In it are included also the concentrated mineral acids (sulphuric, nitric, and hydrochloric); oxalic acid; the alkalies (potash, soda, and ammonia) and their carbonates; acid, alkaline, and corrosive salts of the metals (such as bisulphate of potash, alum, butter of antimony, and nitrate of silver); also carbolic acid. I

The symptoms produced by the mineral acids and the alkalies are almost altogether referrible to local action; but some corrosive poisons, such as carbolic acid, produce, besides a local action, remote and specific constitutional effects. The symptoms of corrosive poisoning are marked and unmistakable, except in infants. Immediately on swallowing the corrosive substance, an acid, caustic, or metallic burning sensation is experienced in the mouth, fauces, gullet, and region of the stomach, and this speedily extends over the whole belly ; as a rule vomiting speedily follows. In the case of the mineral acids, and in oxalic acid poisoning, the vomit is so acid that if it falls upon a marble or concrete floor effervescence ensues. No relief follows the evacuation of the stomach. The ejected matters contain blood, and even fragments of the corroded walls of the alimentary canal. The belly becomes distended with gas, and horribly tender. High fever prevails. The mouth is found to be corroded. Death usually ensues within a few hours; or, if the patient survives, he or she may perish miserably, months after the poison was taken, through starvation consequent upon the gradual contraction of the gullet, brought about by its corrosion and subsequent healing.

The treatment of corrosive poisoning consists in very gently emptying and washing out the stomach by means of a soft siphon-tube. The stomach-pump cannot be used with safety in consequence of the weakening of the walls of the stomach by corrosion. Demulcents and opiates may be subsequently administered. After death from corrosive poisoning the walls of the stomach are found corroded, and even perforated.

1. Corrosive Sublimate.— Here all the signs and symptoms of corrosive poisoning are produced in their severest form. A grain or two of this poison may prove fatal. Fortunately there is an efficient antidote in white of egg, the albumen of which, if administered at once, renders the salt insoluble. The eggs should be divested of their yolks, beaten up with water, and given promptly, repeatedly, and abundantly, followed by emetics. Poisoning by corrosive sublimate may be followed by the specific toxic effects of mercury, such as salivation and tremor.

Workers in mercury, such as water-gilders, looking-glass makers, and the makers of barometers and thermometers, are apt to suffer from a peculiar form of shaking palsy, known as “the trembles,” or mercurial tremor. This disease affects most frequently those who are exposed to mercurial fumes. The victim is affected with tremors when an endeavour is made to exert the muscles, so that he is unable, for instance, to convey a glass of water to the lips steadily, and when he walks he breaks into a dancing trot. The treatment consists in removal from the mercurial atmosphere, baths, fresh air, and the administration of iron and other tonics.

2. Mineral Acids.— These are oil of vitriol or sulphuric acid, aqua fortis or nitric acid, and spirit of salt or hydrochloric (muriatic) acid. These when taken in a concentrated form produce well-marked symptoms of corrosion. When they are diluted, the symptoms are those of an irritant poison. Nitric acid stains the mouth and skin of a yellow colour. The treatment consists in the administration of alkalies or their carbonates, chalk, whiting, or even uncoloured plaster scraped off the walls or ceiling, with the view of neutralizing the acid.

3. Oxalic acid is a vegetable acid. When taken in the state of concentrated solution it acts as a corrosive, but when diluted as an irritant. But it also exerts a specific effect, killing the patient by cardiac syncope not unfrequently within a few minutes. When a person after taking a crystalline substance, tasting strongly acid, dies within 15 or 30 minutes, after the manifestation of great weakness, small pulse, and failure of the heart’s power, poisoning by oxalic acid is almost certain. The treatment consists in promptly administering an emetic, followed by chalk, whiting, or any substance containing carbonate of calcium. The alkaline carbonates are valueless, for the alkaline oxalates are almost as poisonous as oxalic acid itself.

4. The Alkalies.— Potash, soda, and their carbonates and sulphides produce symptoms resembling those of the mineral acids, except that purging is a usual accompaniment.

5. Carbolic acid when taken in the form of a concentrated liquid acts as a corrosive, causing whitening and shrinking of all the animal membranes with which it comes in contact. The patient, however, becomes speedily comatose, the poison acting profoundly upon the great nervous centres. A curious phenomenon—black or dark green urine—is commonly observed after the administration of this poison. Saccharated lime-water, diluted and drunk freely, and a solution of sulphate of soda are perhaps the most useful remedies.

2. Irritant Poisons.

Irritant poisons are of two classes—metallic irritants, and vegetable and animal irritants, these latter being for convenience grouped together. Perhaps none of the irritants act purely as such, the irritant symptoms being usually accompanied by well-marked effects upon the nervous system. An irritant is a substance which causes inflammation of the part to which it is applied,·—usually the alimentary canal. Arsenic is by far the most important of the metallic irritants. Other irritants are the moderately diluted acids, many metallic salts, such as those of antimony, lead, copper, zinc, and chromium. Elaterium, gamboge, aloes, colocynth, and croton oil are good examples of vegetable irritants; and cantharides of animal irritants. Animal and vegetable food when decomposed, or infested with certain organisms known as bacteria, may produce violent irritant symptoms. The symptoms produced by irritant poisons are usually more slow in their development than where a corrosive has been administered. Usually, after an interval, greater or less according to the specific nature of the irritant swallowed, a burning pain is felt in the mouth, throat, and gullet, with a sense of constriction of the parts, and followed by burning pain in the region of the stomach. This is increased, and not alleviated, by pressure, a mark which serves to distinguish the attack from one of ordinary colic. Nausea, vomiting, and thirst ensue, speedily followed by distension of the whole abdomen, which is exceedingly tender to the touch. Ordinarily the vomiting is followed by profuse diarrhoea. Should the poison not be speedily eliminated in the vomited and faecal matters, inflammatory fever sets in, followed by collapse; and death may ensue in a few hours.

There is danger of confounding irritant poisoning with some forms of natural disease, such as gastritis and gastric ulcer, colic, peritonitis, cholera, and rupture of the intestines.

1. Arsenic is a specific irritant poison. Almost all the compounds of this metal are poisonous. The term “arsenic” is, however, most commonly applied, not to the metal itself, but to its loλver oxide, arsenious oxide, which is also known as white arsenic. By whatever channel arsenic is introduced into the system, it invariably affects specifically the stomach and intestines, causing congestion or inflammation. The common sources of arsenical poisoning are the taking of white arsenic, which causes acute poisoning, and the inhalation of dust from arsenical wall-papers and textile fabrics, whereby a chronic form of poisoning is induced.

The symptoms of acute arsenical poisoning do not come on, as in the case of corrosive poisoning, immediately after the poison is swallowed. There is usually an interval of half an hour or so before prominent symptoms supervene. Generally, after a feeling of faintness and depression, an intense burning pain is felt in the region of the stomach, with tenderness on pressure. Nausea and vomiting generally follow, increased by every act of swallowing. Unlike what occurs in ordinary vomiting, the pain and sickness are not relieved by the evacuation of the stomach. Vomiting is followed by purging, blood being frequently distinguishable in the evacuations. There is thirst, a feeble irregular pulse, and a perspiring clammy skin. The victim usually succumbs within eighteen to seventy-two hours; if he survives the latter period, good hopes may be entertained of his recovery. The treatment consists in the use of the stomach-pump, emetics, such as mustard and warm water, demulcents, and the free administration of magnesia emulsion and either freshly precipitated ferric hydrate or dialysed iron. Ferric hydrate, and the solution known as dialysed iron, have the property of rendering arsenious anhydride insoluble.

Chronic arsenical poisoning is usually accidental. The inhalation of arsenical vapours in factories, or of arsenical dust from green wall-papers and in the manufacture of artificial flowers, are common sources of this form of poisoning. Arsenic when thus slowly absorbed into the system produces congestion and inflammation of the mucous membranes, redness and irritation of the conjunctiva?, sore throat, a peculiar eruption of the skin, and diarrhoea. The treatment consists in removal from the poisoned atmosphere, and the administration of tonics.

Arsenic-eating, or the ability of some persons to take relatively large doses of arsenic habitually, is a well-established fact. The cause of this singular immunity from the ordinary results of arsenic is quite unknown.

2. Lead. — The salts of lead, more especially the acetate (sugar of lead), are irritant poisons of no very great activity; and, though occasionally death ensues, recovery is the rule. Chrome yellow, or lead chromate, is a powerful irritant poison. All chromates are, indeed, irritant poisons.

Chronic lead poisoning is a much more common affection than acute irritant poisoning by lead. When lead in any form is slowly absorbed into the system, a peculiar affection results, known as saturnine poisoning, and characterized by two prominent symptoms— colic and paralysis. Workers in lead and its compounds, such as plumbers and painters, are frequently affected by this form of disease. Water, especially soft water or such as is contaminated with sewage, on being passed through leaden pipes or stored in leaden cisterns may become contaminated with lead to a dangerous extent. Acid liquids, such as cider, vinegar, &c., may also contain lead as an impurity. Potmen, who drink beer which has rested for some time in pewter vessels, are also the occasional victims of saturnine poisoning. Water which contains lead in a soluble form to the extent of more than one-tenth of a grain per gallon should not be used for drinking purposes. If more than this quantity be present, the water when placed in a white porcelain dish will become more or less dark in colour on the addition of a few drops of a solution of sulphuretted hydrogen.

The commonest manifestation of chronic lead poisoning is lead •colic,—a peculiar twisting and agonizing sensation around the navel, attended with obstinate constipation. This, like all forms of chronic lead poisoning, is almost invariably attended with a peculiar blue line on the margin of the gums, and when this is present the nature of the affection can scarcely be doubtful. The treatment consists in the free use of purgatives, opiates, and the internal use of potassium iodide, which favours the elimination of the metal through the urine. “Wrist-drop” or lead paralysis is also a common result of the ingestion of lead. It consists in a paralysis of the extensor muscles of the forearm, accompanied by a wasting of that structure. A dropping of the wrist is the result of this degeneration. Baths, the use of galvanism, and the administration of potassium iodide and tonics usually afford relief. Should, however, the patient in any form of lead poisoning be exposed for a lengthened period to the effects of the metal, degenerations of the liver, kidneys, and brain supervene, with fatal results.

Inall cases of lead poisoning removal of the exciting cause is indispensable; the worker in lead must suspend his occupation for a time; the use of contaminated articles of food or drink must cease.

3. Copper. — The soluble salts of copper, such as blue vitriol (the sulphate) and verdigris (subcarbonate and subacetate), are emetic and irritant salts. Their emetic effects usually, but not invariably, secure their prompt rejection by the stomach. Occasionally fatal effects have resulted from their administration. Copper becomes accidentally mixed with articles of dietary in a variety of modes. It is also used for improving the colour of preserved fruits and vegetables. Its deleterious properties when thus used in minute quantities have been both asserted and denied. There is, however, a large body of evidence in favour of the at all events occasional poisonous effects of minute quantities of copper.

4. Zine salts and barium salts, except the quite insoluble barium...