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.
Calomel being not only insoluble, like metallic mercury, in ordinary liquids, but being also non-volatile, there has been still more speculation as to how it could reach the current of the circulation.
According to the classic theory of Mialhe, it becomes, like other mer-curial compounds, changed more or less into the soluble perchloride by the action of the gastric fluids, and is absorbed only to the extent of such change. Mialhe argued from the results obtained by heating together calomel and ammonium chloride in a test tube, but Buchheim and others failed to verify any formation of perchloride in such a mixture at the temperature of the body. Rutherford, experimenting more recently, digested 5 gr. of pure calomel in distilled water, with .02 per cent. of free hydrochloric acid - (the same proportion as in gastric juice) - at 100° F. for seventeen hours, and obtained 1/35 gr. of perchloride, but it is unlikely that even so much as this would be formed in the stomach; and the action of calomel so far differs from that of corrosive sublimate as to render it, clinically speaking, improbable that it only depends upon some formation of the latter. Rabuteau, however, maintains that calomel does become changed into perchloride and metallic mercury; also that this perchloride combining with soda salts forms chloride of sodium, and sets free more of the metal - that under the influence of such changes the compounds are absorbed - acids and alkalies being afterward eliminated, and the metallic mercury in part deposited. In this view, though complex, there seems some analogy with what is known of the behavior of salts of gold, silver, and some other metals, and calomel certainly resembles in action preparations of metallic mercury - otherwise we have no proofs of such direct absorption of it, but rather the reverse.
Various observers have directed attention to the possibility of calomel being rendered soluble in other combinations, e.g., with albumen (Buchheim), or as a double salt formed with chlorides of the blood (Graham). Headland pointed out that bile exerts some solvent power on calomel (Lancet, i., 1858), and Gubler asserts that an excess of various organic materials - albumen, mucous, epithelium - acts similarly; some limit, however, must be placed to this observation, for the excess of mucin in the stomach of a dog entirely prevented the absorption of calomel that had been injected into the stomach (Rutherford, Exper. 38). An experiment of Tuson's is more to the point: he placed in one vessel calomel with dilute hydrochloric acid, and in another the same mixture with a proportion of pepsine: after digestion for an equal number of hours sulphuretted hydrogen was passed into the solutions and produced a black precipitate in that with pepsine, but none in the other, proving clearly the effect of the organic subtance in promoting the solution of the calomel (Medical Times, i., 1872, p. 518). Jeannel pointed out the importance of fatty matters for the solution of calomel: in the presence of an alkaline carbonate, it is readily decomposed with precipitation of gray oxide; of this latter a small proportion is retained in solution by the water, but if a fatty oil be mixed with the alkaline solution, this proportion is very much increased: the same might readily occur in the intestine (Abstract: Schmidt's Jahrb., 1869, Bd. cxliii., s. 9).
It is quite possible, as H. Wood remarks, that in consequence of the varying composition of the intestinal fluids and the complex chemical relations of calomel, its solution and ultimate absorption may be accomplished in several ways: when more chlorides are present some per-chloride may be formed, and when sulphuretted hydrogen is in excess it may produce some amount of soluble sulphide.
Dr. Law, of Dublin, was the first to notice how much the absorption of calomel could be promoted, especially in severe illness, by minute subdivision of the dose, giving, e.g., 1/2 gr. every hour (Dublin Quarterly Journal, xiv., p. 393). Trousseau amply corroborated this observation, and it is, a priori, reasonable, for the smaller quantities more readily come in contact with the intestinal fluids to form the double salts or soluble compounds described.
Bellini indicated a difference in the mode of absorption of calomel according to the condition of the stomach: thus, when taken fasting, only a small amount was at first dissolved, with formation of double chloride of mercury and sodium, and lactate of mercury; more was dissolved in the intestine, under the influence of alkaline carbonate, an oxide of mercury being at first formed, and then a double salt; in the large intestine a sulphide was formed (except in the case of infants). Introduced into the stomach during digestion, it was wholly, or almost wholly, decomposed under the action of proteinous substances, metallic mercury being formed and a soluble albuminate.
From the cellular tissue some calomel may be absorbed, since constitutional effects have been produced by its hypodermic injection when simply suspended in liquid, but the major part remains unabsorbed, and frequently causes abscess.