Many curious customs and superstitions may be traced to this belief. In old medical works one may still read that to eat of a lion's heart is a specific to ensure courage, while other organs and certain bulbous plants are a remedy for sterility. The virtue of all the ancient aphrodisiacs resided in their shape. This notion, which largely affected the early history of medicine, is known as the doctrine of signatures. Certain plants and other natural objects were believed to be so marked or stamped that they presented visibly the indications of the diseases, or diseased organs, for which they were specifics; these were their signatures. Hence a large portion of the ancient art of medicine consisted in ascertaining what plants were analogous to the symptoms of disease, or to the organ diseased. To this doctrine we owe some popular names of plants, such as eye-bright, liver-wort, spleen-wort, etc. The mandrake, from its supposed resemblance to the human form, was credited with marvellous powers, and anyone who will take the trouble to inquire into the folk-lore concerning plants and disease will find that much depends upon the appearance of the remedy. One of the most curious peculiarities of Christianity is its doctrine of a God crucified for sinners. So strange, so repugnant to reason as such a doctrine is, it was quite consonant to the thoughts of those who held the belief in salvation by similars. If Paul said, since by man came death by man came also the resurrection of the dead, the development of the doctrine necessitated that if it is God who damns it is also God who saves. Any casual reader of Paul must have been struck by the antithesis which he constantly draws between the law and the Gospel, works and faith, the fall of man, and the redemption through "the second Adam." The very phrase "second Adam" implies this doctrine, which is summed up in the statement that "Christ hath redeemed us from the curse of the law, being made a curse for us" (Gal. iii. 13).