The human being evolved without clothing and the body was bathed with light throughout the day, but civilization has gone to the other extreme of covering the body with clothing which keeps most of it in darkness. Inasmuch as light and the invisible radiant energy which is associated with it are known to be very influential agencies in a multitude of ways, the question arises: Has this shielding of the body had any marked influence upon the human organism? Although there is a vast literature upon the subject of light-therapy, the question remains unanswered, owing to the conflicting results and the absence of standardization of experimental details. In fact, most investigations are subject to the criticism that the data are inadequate. Throughout many centuries light has been credited with various influences upon physiological processes and upon the mind. But most of the early applications had no foundation of scientific facts. Unfortunately, many of the claims pertaining to the physiological and psychological effects of light at the present time are conflicting and they do not rest upon an established scientific foundation. Furthermore some of them are at variance with the possibilities and an unprejudiced observer must conclude that much systematic work must be done before order may arise from the present chaos. This does not mean that many of the effects are not real, for radiant energy is known to cause certain effects, and viewing the subject broadly it appears that light is already serving humanity in this field and that its future is promising.

The present lack of definite data pertaining to the effects of radiation is due to the failure of most investigators to determine accurately the quantities and wave-lengths of the rays involved. For example, it is easy to err by attributing an effect to visible rays when the effect may be caused by accompanying invisible rays. Furthermore, it may be possible that certain rays counteract or aid the effective rays without being effective alone. In other words, the physical measurements have been neglected notwithstanding the fact that they are generally more easily made than the determinations of curative effects or of germicidal action. Radiant energy of all kinds and wave-lengths has played a part in therapeutics, so it is of interest to indicate them according to wave-length or frequency. These groups vary in range of wave-length, but the actual intervals are not particularly of interest here. Beginning with radiant energy of highest frequencies of vibration and shortest wave-lengths, the following groups and subgroups are given in their order of increasing wave-length:

RÖntgen or X-rays, which pass readily through many substances opaque to ordinary light-rays.

Ultra-violet rays, which are divided empirically into three groups, designated as "extreme," "middle," and "near" in accordance with their location in respect to the visible region.

Visible rays producing various sensations of color, such as violet, blue, green, yellow, orange, and red.Infra-red or the invisible rays bordering on the red rays.

An unknown, unmeasured, or unfilled region between the infra-red and the "electric" waves.

Electric waves, which include a class of electromagnetic radiant energy of long wave-length. Of these the Herzian waves are of the shortest wave-length and these are followed by "wireless" waves. Electric waves of still greater wave-length are due to the slower oscillations in certain electric circuits caused by lightning discharges, etc.

The RÖntgen rays were discovered by RÖntgen in 1896 and they have been studied and applied very widely ever since. Their great use has been in X-ray photography, but they are also being used in therapeutics. The extreme ultra-violet rays are not available in sunlight and are available only near a source rich in ultra-violet rays, such as the arc-lamps. They are absorbed by air, so that they are studied in a vacuum. These are the rays which convert oxygen into ozone because the former strongly absorbs them. The middle ultra-violet rays are not found in sunlight, because they are absorbed by the atmosphere. They are also absorbed by ordinary glass but are freely transmitted by quartz. The nearer ultra-violet rays are found in sunlight and in most artificial illuminants and are transmitted by ordinary glass. Next to this region is the visible spectrum with the various colors, from violet to red, induced by radiant energy of increasing wave-length. The infra-red rays are sometimes called heat-rays, but all radiant energy may be converted into heat. Various substances transmit and absorb these rays in general quite differently from the visible rays. Water is opaque to most of the infra-red rays. Next there is a region of wave-lengths or frequencies for which no radiant energy has been found. The so-called electric waves vary in wave-length over a great range and they include those employed in wireless telegraphy. All these radiations are of the same general character, consisting of electromagnetic energy, but differing in wave-length or frequency of vibration and also in their effects. In effect they may overlap in many cases and the whole is a chaos if the physical details of quantity and wave-length are not specified in experimental work.

JUDGING COLOR UNDER ARTIFICIAL DAYLIGHT

It has been conclusively shown that radiant energy kills bacteria. The early experiments were made with sunlight and the destruction of micro-organisms is generally attributed to the so-called chemical rays, namely, the blue, violet, and ultra-violet rays. It appears in general that the middle ultra-violet rays are the most powerful destroyers. It is certainly established that sunlight sterilizes water, for example, and the quartz mercury-lamp is in daily use for this purpose on a practicable scale. However, there still appears to be a difference of opinion as to the destructive effect of radiant energy upon bacteria in living tissue. It has been shown that the middle ultra-violet rays destroy animal tissue and, for example, cause eye-cataracts. It appears possible from some experiments that ultra-violet rays destroy bacteria in water and on culture plates more effectively in the absence of visible rays than when these attend the ultra-violet rays as in the case of sunlight. This is one of the reasons for the use of blue glass in light-therapy, which isolates the blue, violet, and near ultra-violet rays from the other visible rays. If the infra-red rays are not desired they can be readily eliminated by the use of a water-cell.

ARTIFICIAL DAYLIGHT

There is a vast amount of testimony which proves the bactericidal action of light. Bacteria on the surface of the body are destroyed by ultra-violet rays. Typhus and tubercle bacilli are destroyed equally well by the direct rays from the sun and from the electric arcs. Cultures of diphtheria develop in diffused daylight but are destroyed by direct sunlight. Lower organisms in water are readily killed by the radiation from any light-source emitting ultra-violet rays comparable with those in direct sunlight. From the great amount of data available it appears reasonable to conclude that radiant energy is a powerful bactericidal agency but that the action is due chiefly to ultra-violet rays. It appears also that no bacteria can resist these rays if they are intense enough and are permitted to play upon the bacteria long enough. The destruction of these organisms appears to be a phenomenon of oxidation, for the presence of oxygen appears to be necessary.

The foregoing remarks about the bactericidal action of radiant energy apply only to bacteria in water, in cultures, and on the surface of the body. There is much uncertainty as to the ability of radiant energy to destroy bacteria within living tissue. The active rays cannot penetrate appreciably into such tissue and many authorities are convinced that no direct destruction takes place. In fact, it has been stated that the so-called chemical rays are more destructive to the tissue cells than to bacteria. Finsen, a pioneer in the use of radiant energy in the treatment of disease, effected many wonderful cures and believed that the bacteria were directly destroyed by the ultra-violet rays. However, many have since come to the conclusion that the beneficent action of the rays is due to the irritation which causes an outflow of serum, thus bringing more antibodies in contact with the bacilli, and causing the destruction of the latter. Hot applications appear to work in the same manner.

Primitive beings of the tropics are known to treat open wounds by exposing them to the direct rays of the sun without dressings of any kind. These wounds are usually infected and the sun's rays render them aseptic and they heal readily. Many cases of sores and surgical wounds have been quickly healed by exposure to sunlight. Even red light has been effective, so it has been concluded by some that rays of almost any wave-length, if intense enough, will effect a cure of this character by causing an effusion of serum. It has also been stated that the chemical rays have anÆsthetic powers and have been used in this rÔle for many minor operations.

It is said that the Chinese have used red light for centuries in the treatment of smallpox and throughout the Middle Ages this practice was not uncommon. In the oldest book on medicine written in English there is an account of a successful treatment of the son of Edward I for smallpox by means of red light. It is also stated that this treatment was administered throughout the reigns of Elizabeth and of Charles II. Another account states that a few soldiers confined in dark dungeons recovered from smallpox without pitting. Finsen also obtained excellent results in the treatment of this disease by means of red light. However, in this case it appears that the exclusion of the so-called chemical rays favors healing of the postules of smallpox and that the use of red light is therefore a negative application of light-therapy. In other words, the red light plays no part except in furnishing a light which does not inhibit healing.

Although the so-called actinic rays have curative value in certain cases, there are some instances where light-baths are claimed to be harmful. It is said that sun-baths to the naked body are not so popular as they were formerly, except for obesity, gout, rheumatism, and sluggish metabolism, because it is felt that the shorter ultra-violet rays may be harmful. These rays are said to increase the pulse, respiration, temperature, and blood-pressure and may even start hemorrhages and in excessive amounts cause headache, palpitation, insomnia, and anemia. These same authorities condemn sun-baths to the naked body of the tuberculous, claiming that any cures effected are consummated despite the injury done by the energy of short wave-length. There is no doubt that these rays are beneficial in local lesions, but it is believed that the cure is due to the irritation caused by the rays and the consequent bactericidal action of the increased flow of serum, and not to any direct beneficial result on the tissue-cells. Others claim to cure tuberculosis by means of powerful quartz mercury-arcs equipped with a glass which absorbs the ultra-violet rays of shorter wave-lengths. These conclusions by a few authorities are submitted for what they are worth and to show that this phase of light-therapy is also unsettled.Any one who has been in touch with light-therapy in a scientific rÔle is bound to note that much ignorance is displayed in the use of light in this manner. In fact, it appears safe to state that light-therapy often smacks of quackery. Very mysterious effects are sometimes attributed to radiant energy, which occasionally border upon superstition. Nevertheless, this kind of energy has value, and notwithstanding the chaos which still exists, it is of interest to note some of the equipment which has been used. Some practitioners have great confidence in the electric bath, and elaborate light-baths have been devised. In the earlier years of this kind of treatment the electric arc was conspicuous. Electrodes of carbon, carbon and iron, and iron have been used when intense ultra-violet rays were desired. The quartz mercury-arc of later years supplies this need admirably. Dr. Cleaves, after many years of experience with the electric-arc bath, has stated:

From the administration of an electric-arc bath there is obtained an action upon the skin, the patient experiences a pleasant and slightly prickly sensation. There is produced, even from a short exposure, upon the skin of some patients a slight erythema, while with others there is but little such effect even from long exposures. The face assumes a normal rosy coloring and an appearance of refreshment and repose on emerging from the bath is always observed. From the administration of the electric-arc bath there is also noted the establishment of circulatory changes with a uniform regulation of the heart's action, as evidenced by improved volume and slower pulse rate, the augmentation of the temperature, increased activity of the skin, fuller and slower respiration, gradually increased respiratory capacity, and diminished irritability of the mucous membrane in tubercular, bronchitic, or asthmatic patients. There is also lessened discharge in those patients suffering from catarrhal conditions of the nasal passages. In diseases of the respiratory system, a soothing effect upon the mucous membranes is always experienced, while cough and expectoration are diminished.

The cabinet used by Dr. Cleaves was large enough to contain a cot upon which the patient reclined. An arc-lamp was suspended at each of the two ends of the cabinet and a flood of light was obtained directly and by reflection from the white inside surfaces of the cabinet. By means of mirrors the light from the arcs could be concentrated upon any desired part of the patient.

Finsen, who in 1895 published his observations upon the stimulating action of light, is considered the pioneer in the use of so-called chemical rays in the treatment of disease. He had a circular room about thirty-seven feet in diameter, in which two powerful 100-ampere arc-lamps about six feet from the floor were suspended from the ceiling. Low partitions extended radially from the center, so that a number of patients could be treated simultaneously. The temperature of the room was normal, so that the treatment was essentially by radiant energy and not by heat. The chemical action upon the skin was said to be quite as strong as under sunlight. The exposures varied from ten minutes to an hour.

Light-baths containing incandescent filament lamps are also used. In some cases the lamp, sometimes having a blue bulb, is merely contained as a reflector and the light is applied locally as desired. Light-cabinets are also used, but in these there is considerable effect due to heat. The ultra-violet rays emitted by the small electric filament lamps used in these cabinets are of very low intensity and the bactericidal action of the light must be feeble. The glass bulbs do not transmit the extreme ultra-violet rays responsible for the production of ozone, or the middle ultra-violet rays which are effective in destroying animal tissue. The cabinets contain from twenty to one hundred incandescent filament lamps of the ordinary sizes, from 25 to 60 watts. In the days of the carbon filament lamp the 16-candle-power lamp was used. Certainly the heating effect has advantages in some cases over other methods of heating. The light-rays penetrate the tissue and are absorbed and transformed into heat. Other methods involve conduction of heat from the hot air or other hot applications. Of course, it is also contended that the light-rays are directly beneficial.

Light is also concentrated upon the body by means of lenses and mirrors. For this purpose the sun, the arc, the quartz mercury-arc, and the incandescent lamp have been used. Besides these, vacuum-tube discharges and sparks have been utilized as sources for radiant energy and "electrical" treatment. RÖntgen rays and radium have also figured in recent years in the treatment of disease.

The quartz mercury-arc has been extensively used in the past decade for the treatment of skin diseases and there appears to be less uncertainty about the efficacy of radiant energy for the treatment of surface diseases than of others. Herod related that the Egyptians treated patients by exposure to direct sunlight and throughout the centuries and among all types of civilization sunlight has been recognized as having certain valuable healing or purifying properties. Finsen in his early experiments cured a case of lupus, a tuberculous skin disease, by means of the visible and near ultra-violet rays in sunlight. He demonstrated that these were the effective rays by using only the radiant energy which passed through a water-cell made by using a convex lens for each end of the cell and filling the intervening space with water. This was really a lens made of glass and water. The glass absorbed the ultra-violet rays of shorter wave-length and the water absorbed the infra-red rays. Thus he was able to concentrate upon the diseased skin radiant energy consisting of visible and near ultra-violet rays.

The encouraging results which Finsen obtained in the treatment of skin diseases led him to become independent of sunlight by equipping a special arc-lamp with quartz lenses. This gave him a powerful source of so-called chemical rays, which could be concentrated wherever desired. However, when science contributed the mercury-vapor arc, developments were immediately begun which aimed to utilize this artificial source of steady powerful ultra-violet rays in light-therapy. As a consequence, there are now available very compact quartz mercury-arcs designed especially for this purpose. Apparently their use has been very effective in curing many skin diseases. Certainly if radiant energy is effective, it has a great advantage over drugs. An authority has stated in regard to skin diseases that,

treatment with the ultra-violet rays, especially in conjunction with the RÖntgen rays, radium and mesothorium is that treatment which in most instances holds rank as the first, and in many as the only and often enough the most effective mode of handling the disease.

Sterilization by means of the radiation from the quartz mercury-arc has been practised successfully for several years. Compact apparatus is in use for the sterilization of water for drinking, for surgical purposes, and for swimming-pools, and the claims made by the manufacturers of the apparatus apparently are substantiated. One type of apparatus withstands a pressure of one hundred pounds per square inch and may be connected in series with the water-main. The water supplied to the sterilizer should be clear and free of suspended matter, in order that the radiant energy may be effective. Such apparatus is capable of sterilizing any quantity of water up to a thousand gallons an hour, and the lamp is kept burning only when the water is flowing. It is especially useful in hotels, stores, factories, on ships, and in many industries where sterile water is needed.

Water is a vital necessity in every-day life, whether for drinking, cooking, or industrial purposes. It is recognized as a carrier of disease and the purification of water-supply in large cities is an important problem. Chlorination processes are in use which render the treated water disagreeable to the taste and filtration alone is looked upon with suspicion. The use of chemicals requires constant analysis, but it is contended that the bactericidal action of ultra-violet rays is so certain and complete that there is never any doubt as to the sterilization of the water if it is clear, or if it has been properly filtered before treating. The system of sterilization by ultra-violet rays is the natural way, for the sun's rays perform this function in nature. Apparatus for sterilization of water by means of ultra-violet rays is built for public plants in capacities up to ten million gallons per day and these units may be multiplied to meet the needs of the largest cities. Large mechanical filters are used in conjunction with these sterilizers, and thus mankind copies nature's way, for natural supplies of pure water have been filtered through sand and have been exposed to the rays of the sun which free it from germ life.

Some sterilizers of this character are used at the place where a supply of pure water is desired or at a point where water is bottled for use in various parts of a factory, hospital, store, or office building. These were used in some American hospitals during the recent war, where they supplied sterilized water for drinking and for the antiseptic bathing of wounds. In warfare the water supply is exceedingly important. For example, the Japanese in their campaign in Manchuria boiled the water to be used for drinking purposes. The mortality of armies in many previous wars was often much greater from preventable diseases than from bullets, but the Japanese in their war with Russia reversed the mortality statistics. Of a total mortality of 81,000 more than 60,000 died of casualties in battle.

The sterilization of water for swimming-pools is coming into vogue. Heretofore it was the common practice to circulate the water through a filter, in order to remove the impurities imparted to it by the bathers and to return it to the pool. It is insisted by the adherents of sterilization that filtration of this sort is likely to leave harmful bacteria in the water. Sterilizers in which ultra-violet rays are the active rays are now in use for this purpose, being connected beyond the outflow from the filter. The effectiveness of the apparatus has been established by the usual method of counting the bacteria. Near the outlet of the ordinary filter a count revealed many thousand bacteria per cubic inch of water and among these there were bacteria of intestinal origin. Then a sterilizer was installed in which the effective elements were two quartz mercury-lamps which consumed 2.2 amperes each at 220 volts. A count of bacteria in the water leaving the sterilizer showed that these organisms had been reduced to 5 per cent. and finally to a smaller percentage of their original value, and that all those of intestinal origin had been destroyed. In fact, the water which was returned to the pool was better than that which most persons drink. Radiant energy possesses advantages which are unequaled by other bactericidal agents, in that it does not contaminate or change the properties of the water in any way. It does its work of destroying bacteria and leaves the water otherwise unchanged.

These glimpses of the use of the radiant energy as a means of regaining and retaining good health suggest greater possibilities when the facts become thoroughly established and correlated. The sun is of primary importance to mankind, but it serves in so many ways that it is naturally a compromise. It cannot supply just the desired radiant energy for one purpose and at the same time serve for another purpose in the best manner. It is obscured on cloudy days and disappears nightly. These absences are beneficial to some processes, but man in the highly organized activity of present civilization desires radiant energy of various qualities available at any time. In this respect artificial light is superior to the sun and is being improved continually.