Photogenic Conditions.—Light also has a perceptible influence upon growth: it is a great physiological stimulant. At the present day, physical therapy employs light baths for certain forms of neurasthenia and partial enfeeblement of certain organs; and some biological manifestations, such as the pigments—and similarly the chlorophyl in plants and the variegated colouring of birds—receive a creative stimulus from light.
Light contains in its spectrum many different colours, which act quite differently upon living tissues; the ultra-violet rays, for instance, kill the bacilli of tuberculosis and sometimes effect cures in cases of cancer. Psychiatrists and neuropaths have demonstrated that many colours of light have an exciting effect, while others, on the contrary, are sedative.
Hence there has arisen in medicine a vast and most interesting chapter of phototherapy.
In regard to the phenomena of growth, it has been noted that certain coloured lights are favourable to it, while certain others, on the contrary, diminish or arrest it, as the red and the green.
Phototherapy ought to concern us as educators, especially in regard to schools for the benefit of nervous children: a periodic sojourn in a room lit by calming colours might have a beneficent effect upon epileptic, irritable, nervous children, in place of the debilitating hot bath, or, worse yet, the administration of bromides; while light-baths would be efficacious for weak and torpid children.
But for normal children we must consider the light of the sun as the best stimulant for their growth. A sojourn at the sea-shore, so favourable to the development of children, is now believed to owe its beneficial effects to the fact that the child, playing half naked on the sea-shore, bathes more in the sunlight than he does in the salt water. Gymnastics in the sun, while the body is still only half dry, is what the younger generations should practise on a large scale, if they would bring about the triumph of physiological life.
We must not forget this great principle when, by planning home work for the pupils, we practically keep them housed during the entire day, keeping them for the most part employed in writing or reading; in other words, using their sense of sight, which, if it is to be preserved unharmed, demands a moderate light. The eye ought to rest its muscles of accommodation, and the whole body be exposed to the full light of the sun during the greater part of the day. Let us remember that often the children of the poor live in a home so dark that even in full mid-day they are obliged to light a lamp! Let us at least leave them the light of the street, as a recompense for wretchedness that is a disgrace to civilisation!
According to certain experiments conducted in Rome by Professor Gosio, the light of the sun has an intensive effect upon life. Living creatures reared in the solar light grow and mature earlier, but at the same time their life is shortened; that is, the cycle of life is more intense and more precocious; conversely, in the shade the cycle of life is slower, but of longer duration. A plant matures more quickly in the sun, but its stature is lower than that of a plant in the dark, which has grown far more slowly, but has become very tall and slender and lacking in chlorophyl. Similarly, as is well known, the women in tropical countries attain a precocious puberty, while conversely those of the North attain it tardily; and this fact must be considered in relation to the influence of the sun. A life passed wholly in the sunlight would be too intense; an organism that is exposed a few hours each day to the rays of the sun is invigorated; the interchange of matter (metabolism) is augmented; all the tissues are beneficially stimulated. For this reason sun baths are employed for paralytic and idiot children, and consist in exposing the body of the child, reclining upon its bed and with its head well protected, to the direct rays of the sun for several hours a day; this treatment is found to be most efficacious in giving tone to the tissues and improving the general condition of the system.
Variations in the Growth of Stature According to the Seasons.—One proof of the beneficent influence of heat and sunlight upon the growth of the organism, is afforded by the variations in the rate of growth according to the seasons. Every individual grows more in summer than in winter. Daffner gives the following figures relative to the increase in stature according to the seasons: