_Poultices and the Doctrine of Signatures_.--There was a general impression in the past that the indication of the ailment for which substances are medically useful has been set on them by nature, either through the color, or the form of the plant, or other qualities. In general, the law of similars is supposed to hold in the doctrine of signatures--like cures like. Hence the cornmeal poultice for light jaundice, the flax-seed meal poultice for darker jaundiced conditions and for tendencies to gangrene. The charcoal poultice was employed for this same purpose with no better reason, though some of its efficacy may have been due to oxygen present in the pores of the charcoal. I have already spoken of the appeal to the patient's mind in the use of the cranberry for erysipelas, and various other berries were used in like manner on the doctrine of signatures. _Deterrent Materials and Suggestion_.--Another basic principle in the making of poultices was the use of deterrent, repulsive materials, because these were more effective on the patient's mind. All the ordures were so employed. Goose and chicken excrement was supposed to be particularly efficacious for many of the purposes for which we now use iodine. It was applied over sprains and bruises on the unbroken skin. Cow-dung was employed as a poultice for sprains of the larger joints, especially on the feet and legs, but to be efficacious it had to be applied fresh. I have known, within twenty years, of physicians in two so supposedly cultured parts of the country as Pennsylvania and Maryland, to employ such ordure poultices for the cure of sprains and dislocations, and these physicians had a great reputation among the people of their countryside. They were known especially as good bone doctors, and their use of such deterrent materials instead of decreasing their practices rather added to them.