The very dead Creation, from thy touch,
Assumes a mimic life. But this
And all the much-transported Muse can sing,
Are, to thy splendour, dignity, and use,
Unequal far! Great delegated Source
Of Light and Life, and Grace and Joy below.”
With reference to the vegetable kingdom, we see that the most delicate of the discous plants or flowers turn constantly towards the sun; it is also well known that the change of position of the leaves of plants, at different periods of the day, is entirely owing to the agency of light; plants growing in the shade, or in darkness, are pale, and without their natural and healthy colour—they become ‘etiolated’ or blanched. Gardeners avail themselves of a knowledge of this fact, and, by excluding the light, they obtain celery, lettuce, &c., in a white state. If a potato be placed in a dark cell, with but one small aperture for the admission of light, on germinating, the sprout will turn and grow towards the light, and will continue pale and light until it reaches the light, and becomes fairly exposed to its stimulus, when its natural and healthy colour will be assumed.
Light contributes to the maturity of seeds, fruit, and flowers. Professor Davy found by experiment that red rose-trees, carefully excluded from light, produced roses almost of a white colour. Vegetables are not only indebted to the light for their colour,[3] but their taste and odour are likewise derived from, or at all events greatly influenced by, the same source. Light is also an essential element in the topographical arrangement of plants. The southern slopes of our hills and mountain ranges are always clothed with a more fully developed race of plants than the northern; this depends wholly upon the greater degree of light and heat which the former enjoy. The more free the exposure, the more readily will most plants blossom, and yield a rich fruit; so well is this understood in the grape countries on the Rhine, that the right bank of that river, which faces the sun, is reckoned to be much more valuable than the left, and commands a higher price for its wines.
Turning to the animal kingdom, which is more immediately our province, we find in that portion of nature an equal dependence on light for its proper development and vitality. Animals droop when they are deprived of light; there are instances on record where persons having been long confined in dark places or dungeons (even though well ventilated), their whole complexion has become sallow, their general health deteriorated, pustules, with aqueous humours, have opened out upon their skin, and they have become languid, and frequently dropsical. In the absence of light, there is a predominance of the white fluids of the body; the action of the lymphatic system is exalted, and it imparts to the organization of animals that remarkable blanched appearance called ‘etiolement.’ Hence the well-founded supposition, that the absence of the solar rays of light contributes greatly to the development of scrofula.
“Let in the sun, and you shut out the doctor,” says an old Italian proverb. The effects of the free admission of light, as a point of great importance to the well-being of every individual, has been proved by the experiments of Dr. Edwards, who has shown that if tadpoles be nourished with proper food, and exposed to the renewed action of water (so that their bronchial respiration may be maintained), but are entirely deprived of light, the growth continues, but their metamorphosis into the condition of air-breathing animals is arrested, and they remain in the form of large tadpoles. Dr. Edwards also observes, that persons who live in caves and cellars, or in very dark, narrow streets, are apt to produce deformed children. Rabbits, which were kept in a dark cellar, were affected with mollities ossium, their limbs being useless.