This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
Very small doses, such as 1/30 to 1/15 gr., may be taken for some time without other effects than such as are of stimulant and tonic character - e.g., improvement of appetite, sense of warmth at the stomach, and general invigoration; but usually, sooner or later, these symptoms are replaced by those of irritation and malaise. Trousseau quotes from Koepl the case of a servant who, desiring to get rid of a severe mistress, mixed with her food for some time very small doses of arsenic: the mistress, however, improved in appearance and in stoutness, and the plot was only detected after the use of a large poisonous dose. Doses of 1/10 to 1/2 gr. are liable to produce soreness of mouth, with some salivation and dysphagia, foetid or sour taste, thirst, heat and constriction in pharynx, with nausea or vomiting, gastric pain, flatulence amounting to tympanitis, and diarrhoea. Vaudrey found copious pultaceous stools follow the medicinal use of arsenic without toxic symptoms. One of the early symptoms of the physiological action of the drug is a slimy silvery aspect of tongue, "as if nitrate of silver had been lightly applied" (Beg-bie), an appearance produced by a thin coating of mucus secreted under the influence of irritation. After continued doses, the tongue becomes red or brown, cracked and tremulous, the gums bleed, and the buccal membrane becomes covered with aphthous or even membranous patches like a true diphtheritic condition (British Medical Journal, i., 1862). Vomiting becomes so frequent that all food is rejected, and emaciation sets in rapidly, an effect which has been termed "tabes arsenicalis."
After poisonous doses, which may be stated at 2 gr. and upward, the symptoms already described become intensified; pain especially of most severe burning, cramping, spasmodic character comes on within half to one hour, in the region of the stomach and navel, spreading thence over the whole abdomen, which becomes contracted and hard: the ejecta are offensive, and yellowish or greenish in color, not unlike bile (unless, as often occurs in cases of poisoning, soot or indigo has been mixed with the arsenic); hiccough attends the vomiting and purging; the latter becomes involuntary, and is accompanied with severe tenesmus, and the general symptoms may closely simulate those of cholera (Lancet, ii., 1870).
On the other hand, in some exceptional cases, the vomiting has been only moderate, and there has been complaint of coldness rather than heat; in others, there has been almost entire absence of pain, the patient remaining in a dull and semi-narcotized condition, and in several even severe cases, a remission of symptoms has occurred for some days before death (cf. Taylor: Guy's Reports, 1850).
In experimenting with frogs, Dr. A. Lesser found that intestinal peristalsis was increased by arsenic, and local tetanic contractions occurred from immediate irritation of ganglia in the intestinal coat (not indirectly from influence of the central nervous system): gastro-enteritis was also produced by the drug, but he did not, as Bohm did, find it more poisonous when given by the mouth than by a vein. It was eliminated by the intestinal mucous membrane (Virchow's Archiv, 1878; Lancet, ii.), and we may add here that by whatever channel toxic doses of the drug are given to men or animals, gastric inflammation is commonly determined.