It is a matter of everyday observation that when we leave plants in a room, where no sunshine can penetrate, they lose their color and soon show quantities of parasites. Similar changes occur in persons who live in dark rooms and seldom come into the sunlight. They become pale, and are liable to all kinds of bacillary infections, especially tuberculosis. An Italian proverb says, very justly, “Dove no viene il sole viene il medico”—“Where comes no sun, the physician is coming,” and a German proverb again says, “Auf die schattige seite der strasse kommt der Leichenwagen doppelt so oft, als auf die sonnige,” which means in English, “The funeral coach turns twice as often on the shady side of the street as on the sunny side,” which saying, like most proverbs, contains much truth.
We often notice that on days when there is no sunshine especially when at the same time it is cold and damp, we feel depressed in mind. In such an atmosphere there is a diminution of the respiratory and transpiratory functions of the skin, and, in consequence, a retention of toxic products. On the other hand, on sunny and dry days these functions are facilitated, and there is less work to be thrown upon the kidneys. Such a rest does good to an organ that is almost constantly at work, and is a wise economy for the days of old age. It is astonishing how sunshine can influence our mental condition. We feel better able to work, and also to take outdoor exercise, on sunny days. Particularly in old age is sunshine precious, and we see our old house dog and our cat lying in the sunshine and taking a sun bath. In the same way, instinct tells old people that the sun is good for them, and thus they eagerly watch for it to shine, and like to sit in it, especially on cold days.
It has been shown by exact researches that the sun’s rays can kill bacteria, and statistics have shown that in sunny weather there are fewer infectious diseases, like influenza, than in dull weather. In sunshine there are two elements which possess antitoxic and healing properties: light and warmth. Its light is made use of in the treatment of certain infectious diseases, like lupus (Finsen treatment). Both these properties can be used to great advantage in the sunbath treatment. Lying in the sun for a certain length of time causes a dilatation of the blood-vessels and, later on, abundant perspiration.
The ancient Romans made use of the therapeutic action of sunshine, and many of them took sun baths on the roofs of their houses. There were also public sun-baths, much visited by the population. The ancient physicians recognized the value of sunshine in the treatment of various ailments. According to Hippocrates, the sun-bath augments transpiration and makes us more resistant against disease, giving us more strength. Celsus also advised its use in nervous diseases.
Certain people have undertaken scientific experiments on animals to prove the great effects of light. Moleschott, the great physiologist, found that the embryos of frogs gave off far more carbonic acid under the influence of light than when they were in the dark. The stronger the light the more carbonic acid was given off. Edwards found that such embryos could not develop at all in the dark.
Very important was the discovery of Arloing,[241] and also of Duclaux,[242] that the growth of bacteria when exposed to the sun is checked, and that later on they will even be killed. This is mainly due to the action of blue and ultra-violet rays.
The chemical action of sunlight is exercised by the blue and ultra-violet rays (Finsen), and the heat comes mainly from the red rays. From our point of view, however, the chemical rays play the more important part.
When we sit in the sun for a long time and get an inflamed skin, this is due mainly to the chemical rays. This fact was established by Charcot on the basis of clinical observations. Charcot’s work has been confirmed by the researches of Widmark, and especially by the exact experiments of the famous Danish physician, Niels Finsen,[243] in 1906. The latter showed that when strong light killed bacteria, this was due to the action of the chemical rays alone, and, specifically, to the ultra-violet rays. He also showed that these are the rays which produce dilatation of the blood-vessels and an inflammatory condition of the skin.
To the red cheeks of those people who pass much time in the open air and sun, we can compare, as a contrast, the pale faces with a greenish hue of those who live in the dark, like polar explorers. If strong light dilates the blood-vessels, and sends much blood to the periphery of the body, thus promoting the insensible perspiration and metabolism, on the other hand, in the long night of the arctic regions there is contraction of the blood-vessels, and the blood is kept back in the interior of the body, with the retention of excretory products. It has been shown by Oerum,[244] through experiments on animals, that the quantity of their blood and its percentage of hæmoglobin is dependent upon the light. They are reduced in the darkness and increased in the light. Through a light bath the quantity of blood was increased 25 per cent. within four hours. Finsen[245] has also found, through examination of twenty-nine persons, that there is less hæmoglobin in the blood in winter than in summer, due to the lack of sunlight in winter. Grawitz and Graffenberger have seen a diminution of the hæmoglobin, as also of the quantity of the whole blood, in animals which were kept in the dark. Marti found that the red blood corpuscles are diminished in such animals, but become augmented when they are again exposed for a time to the sunshine.
We should aim to get our share of direct sunlight in the open air, for, as Finsen has shown, the valuable chemical rays of the sun are excluded by glass; and, after all, it is not warmth alone we seek, but also the chemical and anti-bacterial action of the sunlight, together with its effects upon the blood-vessels and nervous system.
To absorb as much of the active rays as possible, it is best to wear light or light blue or light gray clothing, which allows the sun’s rays to pass, whereas dark cloth does not, as found by Boubnoff and Lenkey. The rays of the sun are always valuable, but their action varies with the altitude. Thus, the higher the altitude and the rarer the atmosphere, the more efficacious will be the action of the sun’s rays. In lower altitudes the rays have to pass through dense strata of air filled with vapors of carbonic acid and dust, and thus much of their strength is lost. As Prof. Mohn[246] says in his book on “Meteorology”: “The rays of the sun in transit meet always denser and denser air, which contains large quantities of vapor, carbonic acid, and dust. A part of their strength is absorbed by the substances contained in the air, and these, as well as the air, are heated. Hereby some of the power of the sunshine gets lost, as the rays of the sun are reflected off these substances. Furthermore, they pass through clouds. Hence the rays of the sun lose more and more of their strength before they reach the earth.”
It is also an important fact that the higher the altitude, the more numerous are the chemical rays of the sun which have the greatest heating properties. In high localities sunshine contains much more of the blue and ultra-violet rays, whose wonderful action upon the red blood-corpuscles has been shown by the experiments of Niels Finsen.[247] Not only on the blood, but also on the nerves, they exercise a tonic action. As Niels Finsen has shown, it is due to these blue and violet rays that insects regain their vitality as soon as the sun shines. As Dr. Holm says, it is probably due to these rays that the quantity of red blood-corpuscles and of hæmoglobin is increased at altitudes of 500 or 600 meters above the sea level, as found by Viault[248] and Mintz.[249]
As a logical consequence of the above, we must try to enjoy sunshine on mountains, or on the terraces of high buildings, as there can be no doubt but that sunshine is more beneficial in such places. In high altitudes sunshine is far more warming than lower down, probably due to the fact that the sun’s rays pass fewer strata with vapor and foreign substances, and thus less of their warmth is absorbed. Thus we can explain the observations that, by exposure for a certain time to the rays of the sun on the top of high mountains in mid-winter, erythematous or eczematous eruptions were produced. At such great heights the air is usually very dry, and so there is less loss of heat from the body. Therefore we can sit comfortably in the sun at such heights without an overcoat, even in winter, whereas several hundred meters lower down we should feel cold even with an overcoat on, especially in a coast climate.
Let us be grateful for every ray of sunshine and take advantage of it. Some ladies avoid the sun, but it would be wiser to seek it and, if possible, to expose our whole bodies to its rays. Let us remove all the curtains from the rooms in which we sleep or sit, especially from our work room. In the train let us sit on the sunny side, and not draw the curtain unless we are reading; in short, let us seek the sun wherever it shines. We shall soon observe how much better we feel after a long sojourn in the sun. We have often been surprised at the appearance of patients whom we have sent for a holiday to the Riviera in Egypt or to other sunny places. Thus we have often seen pale patients come back rosy-cheeked and flourishing, and in our own case we have observed the same thing after staying in California, Arizona, Mexico, and Florida for several weeks. There is no denying that, as a rule, those who spend much time in the sun look better and healthier than those who live in dark rooms or offices. It must be understood that we are talking about sunshine at a moderate temperature. But even a somewhat higher temperature, with sunshine, can do no harm, especially to persons suffering from chronic kidney trouble. In old age, as in other conditions of athyroidia, we often find chronic interstitial nephritis and sluggish kidney functions. Therefore we should relieve the kidneys of any overwork and make the skin do more, which can be accomplished by warm sunshine. Old people, if their means allow it, should never be left to pass a winter in cold climates, but should be sent to warm sunny climates like the Riviera, Egypt, or California or Florida in America. They require as much sunshine as possible. Americans may use with great profit the climatological charts of Dr. Charles Denison, of Denver, Colo., which show with great exactness those parts of America where the greatest number of sunny days occur.
Against old age sunlight should be regarded as an excellent protection. It safeguards our kidney functions by promoting skin activity, and it aids the processes of metabolism. It is best used in combination with exercise, like riding or some form of sport, and a daily sun bath. It is our belief that, by such means, both youth and life may be prolonged.
The wonderful effects of sunshine are illustrated by an interesting experiment of Benjamin Franklin. According to Hufeland[250] this savant had received wine from Madeira which he was putting into bottles on his Pennsylvania estate. In this wine he found a few flies, which were apparently dead. The sharp-minded savant put these flies in the July sun of the hot Pennsylvania climate, and before long the life that had been so long interrupted appeared again. The flies became lively and soon flew away. They thus showed the same reaction to the beneficent effects of sunshine as the insects in the above-mentioned experiment of Niels Finsen. The fly is a most objectionable animal, but it possesses one good trait that reconciles me to its existence; and that is that it is so fond of the sunlight that it may thereby serve as an example to those foolish people who do their best to avoid it.