=Pharmacology.= For the following information, I am indebted to the Botanical Department of Parke, Davis & Co., whom I wish to thank for their unfailing courtesy in replying to my inquiries about this little known plant: "Rosin weed is a general name for all species of the genus _silphium_ of which there are more than twenty species; some of these species, however, have special names. Three species are usually mentioned as being used for medicinal purpose. We list them with their synonyms as follows: Silphium perfoliatum, Lin. Indian cup, ragged cup, cup plant, rosin weed. Silphium terebinthinaceum, Lin. rosin weed (true), prairie dock. Silphium laciniatum, Lin. Syn. S. gummiferum, Ell. compass-plant, polar plant, pilot plant, rosin weed. It is more than probable that all the species of the genus are equally effective from a therapeutic point of view." We have always used the fluid extract of the herb. Goss and Hale used the tincture of the fresh leaves and so the homoeopaths have always used it. Since looking into the history of the plant, I recall a remark of that wise old physician, Rademacher, in regard to chelidonium. _Ich bin kein Freund von Extrakten._ He preferred the tincture of the fresh plant. Tinctures of the fresh plant were Hahnemann's preference too, and it may well be that with rosin-weed also, the tincture preserves the medicinal power better than the extract. =Mode of Action.= If the proving of rosin-weed made by Dr. Hall is reliable, we must conclude that rosin-weed cures the symptoms that it produces in the healthy and it must be regarded as acting on the homoeopathic principle. I must own that I am a little suspicious of provings that match so closely the long established popular use of a drug and, in this case, believe that we must wait for confirmation of this proving before accepting it as sound. Rosin-weed has always seemed to me to be a harmless herb, which is shown also by its use among children as chewing gum. I have never noticed the "tonic, diaphoretic or diuretic effects" attributed to it in eclectic medicine and believe that they must be feeble. The only unpleasant effect that I have noted is nausea after large doses, sixty drops or more, and this in very few patients. Vomiting is rare, is never serious and ceases spontaneously when the stomach is empty of the drug.