Treatise on Poisons by Sir Robert Christison

ON THE PHYSIOLOGICAL ACTION OF POISONS. I shall discuss this subject by considering first the mode in which poisons act, and secondly, the causes by which their action is liable to be modified. SECTION I.—_On the Mode of Action of Poisons._ On attending to the effects which follow the application of a poison to the body, we perceive that they are sometimes confined to the part where it is applied, and at other times extend to distant organs. Hence the action of poisons may be naturally considered as _local_ and _remote_. The local effects of poisons are of three kinds. Some decompose chemically or corrode the part to which they are applied. Others, without immediately injuring its organization, inflame or irritate it. Others neither corrode nor irritate, but make a peculiar impression on the sentient extremities of the nerves, unaccompanied by any visible change of structure. We have examples of local _corrosion_ or chemical decomposition in the effects of the concentrated mineral acids or alkalis on the skin, and in the effects of strong oxalic acid, lunar caustic, or corrosive sublimate on the stomach. In all of these instances the part to which the poison is applied undergoes chemical changes, and the poison itself sometimes undergoes chemical changes also. Thus oxalic acid dissolves the gelatin of the animal textures; and in the instance of corrosive sublimate, the elements of the poison unite with the albumen, fibrin, and other principles of the tissues. Of local _irritation_ and its various consequences we have many examples, from redness, its slightest, to ulceration and gangrene, its most severe effect. Thus externally, alcohol reddens the skin; cantharides irritates the surface of the true skin and causes vesication; tartar-emetic causes deep-seated inflammation of the true skin and a pustular eruption; the juice of manchineel[1] spreading inflammation of the subcutaneous cellular tissue; arsenic inflammation of all these textures, and also death of the part and subsequent sloughing. Internally, alcohol reddens the stomach, as it does the skin,—but more permanently; while other substances, such as the diluted mineral acids, arsenic, cantharides, euphorbium, and the like, may cause all the phenomena of inflammation in the stomach and intestines, namely, extravasation of blood, effusion of lymph, ulcers, gangrene. Many of these irritants, such as arsenic, are in common speech called corrosives; but they have not any power of causing chemical decomposition: if they produce a breach in the texture of an organ, it is merely through the medium of inflammation and its effects. Of _nervous impressions_, without any visible organic change, few well authenticated and unequivocal instances are known. A good example has been mentioned by Sir B. Brodie in the effect of monkshood on the lips when chewed,[2] an effect which I have also often experienced: it causes a sense of numbness and tingling in the lips and tongue, lasting for some hours, and quite unconnected with any affection of the general nervous system. Another instance, first mentioned to me by M. Robiquet, and which I have verified, occurs in the effects of the strong hydrocyanic acid: when this acid is confined in a glass tube with a finger on its open end, the point of the finger becomes benumbed, exactly as from the local action of great cold. These are undoubted instances of a purely nervous local impression on the external surface of the body. The most unequivocal instance I know of a similar impression on internal parts is a fact related by Dr. W. Philip with regard to opium.[3] When this poison was applied to the inner coat of the intestines of a rabbit during life, the muscular contractions of the gut were immediately paralyzed, without the general system being for some time affected. The same effect has been observed by Messrs. Morgan and Addison to follow the application of ticunas to the intestine:[4] an instant and complete suspension of the peristaltic movement took place as soon as it touched the gut. A parallel fact has also been described by Dr. Monro, _secundus_:[5] when an infusion of opium was injected between the skin and muscles of the leg of a frog, that leg soon became palsied, while the animal was able to leap briskly on the other three. Analogous results have farther been obtained with the prussic acid by M. Coullon.[6] He remarked, that when one hind-leg of a frog was plunged in the acid, it became palsied in thirty-five minutes, while the other hind-leg continued perfectly sensible and irritable. Acetate of lead probably possesses the same property. These facts are important, because some physiologists have doubted whether any local impressions of a purely nervous nature, unconnected with appreciable organic change, may arise from the action of poisons. Yet the existence of impressions of the kind is essential to the stability of the doctrine of the sympathetic operation of poisons,—that is, of the transmission of their influence from organ to organ along the nerves. Nay, in the instance of many poisons supposed to act in that manner, we must still farther believe in the existence of primary nervous impressions, which are not only unconnected with organic change, but likewise undistinguishable by any local sign whatsoever. Of the three varieties in the local effects of poisons—corrosion, irritation, and nervous impressions,—the first two may take place in any tissue or organ; for example, they have been observed on the skin, on the mucous membrane of the stomach, intestines, windpipe, air tubes, bladder, and vagina, in the cellular tissue, in the serous membranes of the chest and abdomen, in the muscular fibre. We are not so well acquainted with the nature of local nervous impressions on different tissues; but it is probable that in some textures of the body they are very indistinct. So much for the local effects of poisons. On tracing the phenomena which follow more remotely, we observe that the affected part sometimes recovers without any visible change, sometimes undergoes the usual processes consequent on inflammation, sometimes perishes at once and is thrown off; and if the organ is one whose function is necessary to life, death may gradually ensue, in consequence of that function being irrecoverably injured. The purest example of the last train of phenomena is to be seen in the occasional effects of the mineral acids or alkalis: death may take place simply from starvation, because the inner surface of the stomach and intestines is so much injured that a sufficient quantity of nutriment cannot be assimilated. But death and its antecedents can seldom be accounted for in this way. For symptoms are often witnessed, which bear no direct relation to the local injury: death is generally too rapid to have arisen from the function of the part having been annihilated: and the rapidity of the poisoning is not proportional in different cases to the local injury produced. Even the mineral acids and alkalis seldom kill by impeding or annihilating digestion, because they often prove fatal in a few hours; and among other poisons there are few which ever cause death simply by disturbing the function of the part primarily acted on. Death and the symptoms preceding it arise from an injury of some other organ, to which they are not and cannot be directly applied. We are thus led to consider their remote action. The term _remote_ is here used in preference to the common phrase _general_ action, because the latter implies an action on the general system or whole body; whereas it appears that an action of such a kind is rare, and that most poisons which have an indirect action exert it on one or more of the important organs only, and not on the general system. There is not a better instance of the remote action of poisons than oxalic acid. It has been already mentioned that concentrated oxalic acid is a corrosive: yet it never kills by destroying the function of the stomach. Man, as well as the lower animals, will live several days or weeks without nutriment. Now this poison has been known to kill a man in ten minutes, and a dog in three minutes only. Neither does it always induce, when swallowed, symptoms of an injury of the stomach; for death is often preceded by tetanus, or apoplexy, or mortal faintness. Nor is the violence of the poisoning proportional to the extent of the local injury: in fact, death is most rapid under circumstances in which the stomach is least injured, namely, when the acid is considerably diluted.[7] Let us now proceed to enquire, then, in what way the influence of a poison is conveyed from one organ to another. Here it will at once be perceived that the conveyance can be accomplished in one of two ways only. Either the local impression passes along the nerves to the organ secondarily affected; or the poison enters the bibulous vessels, mingles with the blood, and passes through the medium of the circulation. In the former way poisons are said to act through _sympathy_, in the latter, through _absorption_.