Sometimes the irritant action of iodine appears to be directed peculiarly to the brain, and the phenomena of nervous disorder predominate; such as neuralgic pains, headache particularly frontal, pains in the eyes and ears, tinnitus aurium, disordered vision, wakefulness, and occasionally delirium and convulsions. Lugol mentions cases of this kind, which resulted from the external use of iodine in the form of bath; so that the effects are something more than the sympathetic results of an irritated stomach. Sometimes symptoms of asthma are said to be produced, ascribable to the influence exerted upon the nervous centres of the par vagum. The name of iodic intoxication has been given to this condition. I have never witnessed other effects of the kind than neuralgic pains and headache; the latter of which is not very uncommon. I once saw an attack of exceedingly severe neuralgia, which I ascribed to the use of iodine, and which ceased after the omission of the medicine.

Poisonous Effects

These are of two kinds; first, those which proceed from a prolonged use of iodine in excess; and secondly, those occasioned by an excessive dose at once. Both, I believe, are the result of irritation, produced either in the primae viae, the system at large, or the two jointly.

The name of iodism has been given to the state of system, resulting from the repeated or prolonged exhibition of the medicine in undue amount. it is said to be characterized by vomiting and purging, one or both; abdominal pain; a general febrile state, with heat of skin, frequent pulse, and thirst; cramps in the extremities, and great emaciation, ending in death, if the cause continue to operate. Such cases are seldom seen now. They were probably cither the result of a sustained gastroenteritis, or mere coincidences with the use of iodine, and not effects of it. it would appear, however, from the statements of M. Rilliet, that exceptional cases occur, in which the long-continued use of iodine, even in small doses, occasions emaciation, palpitations, frequency of pulse, trembling, nervous irritability, and general debility; and that these results are most apt to happen among the inhabitants of certain localities where it may be presumed that there is a natural deficiency of iodine in the air, drink, and food. This suggestion is of some importance; as it may serve to account for certain otherwise inexplicable cases of marasmus, which may occur from change of residence from such a locality to another where iodine abounds, as near the sea. (Ann. de Thérap., 1859, p. 187.) When the iodide of potassium is used largely for a long time, during whole years for example, it is said to occasion a chronic inflammation of the tongue, by which that organ becomes enlarged, lobulated, and fissured. Several cases of this nature have been reported by Mr. Langston Parker, of England. (U. S. Dispensatory, 11th ed., p. 1221.)

Lebert describes a kind of iodic poisoning which he has observed in patients affected with goitre, and in those only, consisting in a progressive emaciation which may become excessive in a few months, restlessness, incapability of mental concentration, disturbed sleep, frequent pulse, impaired digestion, and not unfrequently dyspnoea and palpitations, without organic lesion. He has found these phenomena to occur in those cases in which the goitre disappeared under the use of the medicine, and ascribes the result to the too rapid absorption of the matter of the thyroid tumour, and its presence in the circulation, where it may act as a poison. Though I have known repeated instances in which goitre has rapidly disappeared under the use of iodine, I have never met with these cachectic phenomena; perhaps because the tumours have been much less developed than those which occur among the inhabitants of the Alps.

Acute poisoning may result from excessive doses of iodine;, though, when taken largely in the unaltered state, it is apt to excite vomiting, and thus obviate any very serious consequences; while in the form of iodide of potassium, in which it is more generally administered, it is very doubtful whether it can be justly considered as poisonous, at least not more so than nitre, and probably under similar circumstances. iodine, however, either in the aggregate state, or that of alcoholic solution, is capable of producing death. This has been proved by experiments on the lower animals, and by the occasional result of over-doses accidentally taken in man. The symptoms are those of irritation and inflammation of the primae viae; namely, violent burning pain in the throat and stomach, intestinal pains, retching or vomiting, purging, thirst, very frequent pulse, palpitation, suffused eyes, restlessness, trembling, faintness, and prostration; and, if death does not soon take place, great emaciation. As to the quantity required to produce fatal effects, there can be no precise decision, as circumstances so much modify the result. Thus, when the iodine happens to vomit early and freely, it is less likely to cause death; and, if taken with substances containing starch, as bread or farinaceous food in general, or if the stomach happen to be full of such food at the time, it is apt to combine with the starch, and thus form a substance comparatively harmless. Orfila found that in dogs, with the oesophagus tied, a drachm of free iodine was sufficient to destroy life in a few days; while in others, in their ordinary condition, two or three drachms were required. A case of death in a woman is on record, caused by swallowing an ounce of the tincture, containing somewhat less than a drachm of iodine. ( Taylor on Poisons, p. 304.) Orfila took four grains and a half of solid iodine, with the effect of producing heat, constriction in the throat, epigastric pains, vomiting, colic, hot skin, frequent pulse, and high-coloured urine, which yielded to emollients and diluents, leaving on the following day only a sense of weariness. Dr. Taylor thinks that fifteen or twenty grains of solid iodine might endanger life (ibid., p. 304); and no prudent physician would approach this quantity, under any circumstances whatever.