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.

Signature Details.—Some of the details of the doctrine of signatures are amusing. For a considerable period nuts were supposed to be a good brain food, and some traces of this idea are still extant, although there does not seem to be any better reason for it than the fact that many nuts have an arrangement of their lobes which resembles the conformation of the brain. On the same principle the Chinese use ginseng-root as a general tonic. The extract is not {36} of any special significance in medicine, though it has come to be much advertised in recent years, and the Chinese continue to pay high prices for it. The reason is that the root of the ginseng plant often resembles the human body. The more nearly this resemblance can be traced, the more virtue there is for the Chinese in the particular specimen of ginseng. The signature is on the roots. It is good for man because it looks like man, just as the nuts are good for the brain because they look like the brain. In modern times we are likely to think that we are far away from any such self-deception. But our deceptions have a more appealing pseudo scientific element in them. Fish was for some time considered a good brain food because fish has phosphorus in it and so has the brain. The two reasons have as much connection as that between nuts and the brain; or ginseng and man.

Astrological ideas came in to help out ignorance and foster supposed knowledge. The sun and the stars were favorable planets and the moon unfavorable. If anything about a plant reminded the gatherer of the sun or the stars, then that plant was sure to be beneficial, especially in chronic diseases. If anything reminded him of the moon, however, then it could be expected to be maleficent in influence. Though childish, this had yet its power to help.

The use of nitrate of silver, which in the old days was called lunar caustic, because it had, in a fresh state, a silvery, moon-like sheen, was largely a matter of signatures. The signature went both by similitude and by contrary. Since the lunar caustic supposedly had a moon quantity, therefore it would be good for moon-struck people—the lunatics of the old time and of our own time. As a consequence nitrate of silver was used in many obscure nervous and mental diseases. In epilepsy it was commonly employed. Even in our own times, entirely on empiric grounds, it was used for such severe organic nervous diseases as locomotor ataxia and sometimes to such an extent as to produce argyria. Undoubtedly, its use, with confidence on the part of the physician and suggestion and persuasion on the part of the patient, did much to relieve sufferers from discouragement and from such psychic disturbance of their general health as would have made their condition seem worse.

Wines as Remedies.—How much suggestibility means in the choice of remedies that of themselves are more or less indifferent, may be well judged from the recommendations with regard to various wines that have been made by physicians. At one time and place it is red wine, at another it is white wine that is particularly effective. For certain nations the stronger wines, as Port or some of the Hungarian wines, have appeared to exercise specific effects. Except for the tastiness of these various brands or for other trivial accessories, it is probable that the therapeutic efficacy of the wine depends entirely on the alcohol and the effect of this upon the patient. In his "Memories of My Life," Francis Galton relates that Robert Frere, one of his fellow pupils with Prof. Partridge, who became through marriage in later years a managing partner in a very old and eminent firm of wine merchants, told him that the books of the firm for one hundred and fifty years showed that every class of wine had in its turn been favored by the doctors.

In prescribing wine the doctrine of signatures probably had more to do with the special choice than anything else. Red wines were recommended for anemic people, because somehow the coloring was supposed to affect the {37} patient in such a way as to make up for the lack of coloring in the blood. On the other hand, the light, and especially the straw-colored wines, were recommended for liver troubles, because of their relation in color to the yellow of bile. Light wines were best for people who had more color than normal. Some wines are much stronger than others, and the alcohol, as in so many of our patent medicines, had a stimulating tonic effect, but in olden times this was supposed to constitute only the smallest portion of the efficiency of the wine, while the ingredients that made its color and taste were extremely important. The taking of red wine by anemic patients often proved suggestively valuable, and the alcoholic stimulation led them to eat more freely and look at things more hopefully and, consequently, to improve in health more rapidly than would have been the case had they not had the feeling that somehow they were actually consuming elements that would make their blood red.

Precious Stones.—The doctrine of signatures applied particularly to precious stones, and many of the popular medical superstitions with regard to precious stones were founded on it. The blood stone was said to be efficient as a tonic: it stimulated people: it made the anemic stronger and ruddier if it were worn on the fingers. The torquise turned pale when its owner was in poor health. It was the stone that was an index of what has been called "the blues" or what one modern writer has dignified by the title "splanchnic neurasthenia." Dr. Donne wrote of:

A compassionate turquoise that doth tell
By looking pale, the owner is not well.

It is probable that the pallor of the patient's hands as the background to the stone made the difference in its appearance thus noted. It became deeper in hue, as it were, when people were in ruddy health. The suggestive influence of such beliefs is easy to understand. It is even possible that the wearing of an amethyst did help to keep people from indulging in liquor to excess, for that is the traditional effect of the wearing of this stone, though its virtue seems to be founded on nothing better than the supposed derivation of the name from the Greek a privative and methuo, "I get drunk," suggesting strongly to the wearer that he should not get drunk.

The jacinth superinduced sleep and doubtless the strong suggestion of this supposed influence helped many sufferers from so-called insomnia to get sleep. The single fixed idea that now they must get to sleep would greatly help them. Pillows in the olden time were occasionally set with bits of jacinth, and there is even the record of bed-linen embroidered with it. This would probably be quite as effective as are hop-pillows in the modern time, for their main influence, as is also true of pine pillows, seems to be through suggestion. Some other traditions with regard to precious stones are harder to understand, yet may be explained. The owner of a diamond was supposed to be invincible. Diamonds represented money and money meant power. It is harder to explain the tradition that the possession of an agate made a man able and eloquent.

The wide acceptance of the doctrine of signatures, and of allied ideas, as to the effect of precious stones and metal and jewelry upon disease, makes {38} it clear that the acceptance of a mental persuasion with the changes in habits that follow, may serve as the basis of a successful system of therapeutics. The materials associated with the idea had absolutely no more physical influence than does the carrying of a horse chestnut or a potato in the pocket serve to keep off rheumatism.