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.
During certain stages of this malady, preparations of aconite, iron, iodine, bromine, etc., are indicated, as described under those medicines; but at the time when pus is commencing to form, and the false membrane is becoming somewhat loosened from the mucous surface, the sulphide of calcium is often useful, for it exerts the action already referred to, of assisting to healthy completion and at the same time limiting the extent of the suppurative process. We know that this formation of pus-cells occurs as part of the diphtheritic inflammation before the return of healthy conditions, and, as remarked by Mackenzie (who does not, however, mention this remedy), "when it is found impossible to check the formation of lymph, it is rational treatment to convert, as far as we can, the inflammatory into a suppurative process" ("On Diphtheria," 1879). If commenced early in this stage, in doses of 1/10 to 1/4 gr. every one or two hours, it produces the best effects; but it is useful also even if begun after pus-formation is fully developed, and I believe it has some influence in lessening blood-poisoning. The value of steam-inhalation in helping on the natural changes of diphtheria and the formation of muco-pus and loosening of the membranes has been often proved (P. James, Oertel), and is now well known. I find it still more efficacious if the sulphide of calcium be added to the boiling water in the proportion of about 4 gr. to the pint, so that a certain amount of sulphurous vapor is locally applied.
The local insufflation of finely powdered sulphur has been credited with arresting the development of diphtheritic exudation (Practitioner, November, 1868, vi.), but has disappointed expectation. Oertel concludes, after much experience, that it acts only as a "scouring powder," wearing off the membranes by friction; it has no influence at the onset of the malady, but has seemed to answer only when purulent infiltration and fibrinous exudation have already ceased. It has an antizymotic, but no other specific power, and is liable to cause irritation (British Medical Journal, January 11, 1879).
Mr. Erskine Stuart has, however, written still more recently in favor of local applications of precipitated sulphur. According to his latest experience, "it is best applied, after being rubbed up with a little water, on a swab to the affected part; it is free from grittiness, it sticks better, and hence exerts its action for a longer time, and is applied more safely in this manner than by insufflation." He states "that every case treated with sulphur made a rapid recovery" (Practitioner, October, 1879), but the number apparently is not more than six, and he unduly depreciates other remedies.
In Laryngo-tracheal Diphtheria (Croup), when we cannot always see the false membrane, I find the sulphide of calcium treatment indicated if wheezing, rattling sounds accompany the breathing, i.e., when the membrane begins to be loosened, rather than in the first stage, when the breath-sounds are of dry and sawing character.