_Similia similibus curantur_, like is cured by like, is a very old idea. According to the doctrine of signatures nature had put an external natural marking or a symbolical appearance or characteristic upon a plant, mineral or other object, to indicate its special usefulness for the treatment of certain diseases or for affections of certain organs. Sir Robert Boyle, sometimes spoken of as the father of chemistry, said, "Chymists observe in the book of nature that those simples that wear the figure or resemblance, by them termed signature, of a distempered part, are medicinal for that part or that infirmity whose signature they bear." On this principle yellow flowered plants were good for jaundice, because they resembled it in color. The blood stone was good for hemorrhage, and plants of certain forms were good for the organs or parts of man which they resembled. Certain plants were named with this idea. Kidneywort, liverwort, are typical examples. Scorpion grass, our familiar forget-me-not of the _genus myosotis_, was so-called because its spike resembled a scorpion's tail and was, therefore, good against the scorpion's sting, or against pains similar to that produced by such a sting. Some of the resemblances were extremely far-fetched, but in spite of the defect of nature's signature on them, they seem to have been effective in therapeutics. The plant, sometimes called Jew's ear, which can by an effort of the imagination be made to bear resemblance to the human ear, was, for instance, supposed to be a successful cure for diseases of that organ. We know now that there is no significance in this doctrine of signatures. It represented one phase of pseudo-science. But the idea of itself was enough to help people to throw off many symptoms, to relieve discouragement, to encourage them with the thought that they ought to get better; accordingly they took new heart, ate better, went out more, and as a result naturally slept better, and then nature did the rest. Signatures are an exquisite example of pure psychotherapy, as the initial agent and natural curative methods accomplishing the cure.