Hahnemann directed it to be prepared as follows : "Take a piece of recently prepared quicklime weighing about two pounds, immerse it for a minute in a vessel full of distilled water, and then lay it in a dry cup, where it soon becomes pulver- ized, giving out much heat and a peculiar odor called the vapor of lime. Of this fine powder you take two ounces, place it in a mortar which had been previously warmed, and then mix it with a solution of two ounces of the bisulphate of potash in two ounces of boiling-hot water, the potash before being dissolved having been exposed to a red heat, melted, cooled again and then pul- verized. "This thickish preparation is inserted into a retort, to the open end of which the receiver — which ought to be dipped in water to half its height — is hermetically fastened. The liquid is distilled over by gradually approaching a coal fire 3l8 CAUSTICUM. to the retort, and until the preparation is perfectly dry. The liquid in the receiver is about one ounce and a half, as clear as water, and containing the Causticum in a concentrated form. It smells like the lye obtained from potash, and has an astringent and burning taste on the back part of the tongue. Its freezing point is below that of water ; it promotes the putrefaction of animal sub- stances that are placed in it ; with the salts of baryta it gives out no trace of sulphuric acid, nor any trace of lime- earth with the oxalate of ammonium," Dr. Black had several specimens analyzed, and believes Causticum to be a weak solution of potassic hydrate. Others deny any virtue to it, and reject it from the materia medica ; but to this proposition we oppose the physiological and the pathological tests. The symptoms ascribed to Causticum are very many. Instead of giving a resume of all, I will call your attention to certain groups, of which the value has been abundantly established by clinical experience.