As illustrative of the power of the imagination, the so-called blue-glass mania, which prevailed extensively in this country, affords a striking example. About the year 1868, General Augustus J. Pleasanton, of Philadelphia, made some experiments to determine whether or not rays of sunlight passing through colored glass had any therapeutic effect on animals and plants. His selection of blue glass as a medium was probably based upon the theory that the blue ray of the solar spectrum possesses superior actinic or chemical properties.

Experimenting first on plants, he adopted the method of inserting panes of blue and violet glass in the roof of his grapery, and noticed as a result an apparent extraordinary rapidity and luxuriance of growth of the vines, and later a correspondingly large harvest of grapes. Encouraged by this success, he built a piggery, having a glass roof, of which one portion was fitted with panes of blue glass, and the other with ordinary transparent glass. It was claimed that the pigs kept under the former developed more rapidly than those under the latter. An Alderney bull-calf, which was very small and feeble at birth, was placed in a pen under violet glass. In twenty-four hours it was able to walk and became quite animated. By the same method a mule was reported to have been cured of obstinate rheumatism and deafness. Again, a canary-bird, which had been an exceptionally fine warbler, declined to eat or sing, and appeared to be in a feeble state of health. The bird in its cage was placed in the bath-room of its owner's dwelling, the windows of which contained colored-glass panes. It was alleged that the little creature speedily improved; its voice became sweeter and more melodious than ever, while its appetite was simply voracious.

Notable cures of human beings were also reported. Cases of neuralgia and rheumatism were said to have been benefited, the development of young infants vastly promoted, while as a tonic for producing hair on bald heads, blue glass was a veritable specific. During the year 1877 popular interest in the craze reached its culmination. In this country the furore assumed national proportions. Peddlers went from door to door in the cities, selling blue glass, and did a thriving business; while many instances of remarkable cures effected by the new panacea were recorded in the newspapers. Then after a time came the reaction; the whole theory became a subject for ridicule and satire, and the public mind was ready to turn its attention to some other fad.

But in spite of the fickleness of the popular mind, this well-known fact remains, that a good sun-bath, with or without the medium of colored glass, is often of great hygienic value. There is truth in the Italian proverb: Dove non va il sole, va il medico: where the sunlight enters not, there goes the physician.

I have thus attempted briefly to describe the blue-glass mania, because it seems aptly to illustrate the healing force of the imagination. So long as people have confidence in blue glass and sunlight combined, to cure fleshly ills, these agents undoubtedly act in many cases "like a charm," and may be classed as mental curatives.

In recent years, however, efforts have been made to determine whether certain colored rays of the spectrum were more potent than others therapeutically. Under the caption "Light-Cures, Old and New," in "Everybody's Magazine," October, 1902, Arthur E. Bostwick, Ph.D., remarks that there was a germ of truth in the blue-glass craze, for it has recently been shown that the red rays are injuriously stimulative in eruptive diseases, and of course the blue glass strained these rays out. It goes without saying that if there were simply health-giving qualities in the blue rays and no injurious ones in the red and yellow, ordinary light would be as effective as that which had passed through blue glass; for the glass introduces no new quality or color into the light; it only absorbs certain rays of the spectrum, allowing others to pass. If blue light, therefore, is more healthful than white, it must be because the remainder of the spectrum has an injurious effect.

An Austrian physician, Dr. Kaiser, has recently asserted, in a paper read before the Vienna Medical Society, that blue light is effective in reducing inflammation, allaying pain, and curing skin-disease, especially by promoting absorption of morbid humors. He asserts that a beam from a powerful lantern, after passing through blue glass, will kill cultures of various bacilli, when directed upon them at a distance of fifteen feet for half an hour daily during six days.