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worship now took place within and not without the sacred building; there is also an artistic reason for the neglect of external form in the basilica.

So long as Hellenism was dominant, architects had no feeling for internal spaces. The building was a mass to be regarded externally; and its claim to beauty rested on the harmony of its stereometric proportions. Roman builders were the first, as Riegl has acutely remarked, to treat space as a material, with what consummate effect the interior of the Pantheon would suffice to show. But in the later Imperial period it was no longer simple space problems which called for solution. The love of effects attained by chiaroscuro and colour led to the articulation of the internal space by windows, and to the invasion of the remaining background by figure-subjects usually executed in mosaic. Such problems were certainly attacked in the third century; and an example of their solution remains in the building known as the Temple of Minerva Medica, really a thermal construction belonging to the Gardens of Gallienus. But it was in the Christian architecture of the fourth century, whether of the central' type, as in S. Costanza, or of the basilican form, that the latest triumphs of Roman art were won. Dr Richter's splendid publication has enabled us to form some idea, not merely of the wealth of imagery with which Christian artists enriched the buildings enshrining the highest acts of Christian worship, but also of the subtle colour-sense which had not yet been dazzled by the jewellery of the East. The gamut of tints in which sky and landscape were composed throughout the historical scenes in the mosaics of S. Maria Maggiore reveal a marvellous delicacy of perception in the artist, and form, as it were, a radiant after-glow of classical art. It is significant that, as Dr Richter shows, no gilding was used in the original decoration. Pure Orientalism, with its love of precious materials for their sheer intrinsic splendour, has not yet finally prevailed, as it was soon to do at Byzantium; and as the sun sets on ancient art, beauty is once more conceived as the harmonising union of matter and spirit.

H. STUART JONES.

Art. VII.-THE LIGHT-TREATMENT OF DISEASE.

1. Meddelelser fra Finsens Medicinske Lysinstitut. By Niels R. Finsen. Parts I-IX. Copenhagen: Gyldendalske Boghandel-Forlag, 1899-1904.

2. Om Bekaempelse af Lupus vulgaris. By Niels R. Finsen. Copenhagen: Gyldendalske Boghandel-Forlag, 1903. 3. Photothérapie, Photobiologie. By L. E. Leredde et L. M. Pautrier. Paris: C. Naud, 1903.

And other works.

NIELS RYBERG FINSEN, famous throughout the world for his treatment of Lupus and other diseases by means of light, was born on December 15, 1860, at Thorshavn in the Faroe Islands. His family were of Icelandic origin. He studied at Reykjavik, the capital of Iceland, and in 1890 took his medical degree in Copenhagen. For three years after this he held the post of prosector of anatomy in that university, but gave it up in order to devote himself to the work that he had mapped out for himself, and continued to pursue till his death on Sept. 24, 1904.

His first contribution to the subject of the effects of light on the skin appeared in 1893. He made many experiments in this direction, and in 1896 published a short paper on the medical application of the light-rays. During the eleven years which intervened between his first publication on light and his death, Finsen held steadily on his way, notwithstanding severe chronic illness. Thanks to his energy, and at first mainly through the private munificence of MM. Hagemann and Jørgensen, a Light Institute was built in Copenhagen. Subsequently the State lent its assistance; and Finsen himself generously handed over to the Light Institute and the Sanatorium for diseases of the heart and liver the greater part of the proceeds of the Nobel prize awarded to him for his work. Our own Queen Alexandra has taken the greatest interest in Finsen's discoveries, and has shown her usual practical sympathy by the gift of the Finsen apparatus to the London Hospital. The Copenhagen Institute comprises, in addition to the installations and rooms for the treatment of patients, an experimental laboratory, where the subject of light is thoroughly investigated.

In order to comprehend the principles and methods

of light-treatment, a brief preliminary discussion of the laws and composition of light is desirable. When a beam of white light is passed through a slit and caught upon a glass prism, the rays are refracted in an unequal manner, giving rise, if received on a screen, to a rainbowlike band varying in colour from red to violet. This is called the spectrum, which is made up of seven principal regions-red, orange, yellow, green, blue, indigo, and violet. These rays vary in refrangibility, becoming increasingly refrangible from red to violet; and also in wave-length, which increases from violet to red. The solar spectrum exhibits a number of transverse dark lines, due to absorption by gases either in the sun's atmosphere or in that of the earth. It is by a study of these lines that the presence of various terrestrial elements in the sun's atmosphere has been discovered, including helium, which appears to be an emanation from radium.

But the radiation from the sun does not consist only of rays perceived by the eye. There are rays of greater wave-length than the red and others of less wave-length than the violet rays; they form the invisible spectrum, the regions beyond the luminous band being called the infra-red and the ultra-violet respectively; the latter can be brought out by photography. This has led to a division of the solar spectrum into three kinds of rays, the invisible heat rays (red and infra-red), the luminous rays (red to violet, that is, the whole of the visible spectrum), and the chemical or actinic rays (violet and ultraviolet). This division is not strictly correct, as it has been shown that the nature of the surface on which the rays fall is also a factor in the effects observed; but, for present purposes, the threefold division will serve.

Before considering light in its biological aspect, its influence on chemical compounds must be briefly described. Scheele long ago called attention to the changes brought about in chloride of silver when exposed to light. The decomposition of silver nitrate is a well-known phenomenon, which is used, for instance, in photography. Other salts, such as iodide of lead, chloride of gold, and some iron salts, are also decomposed by light. Chemical combinations are likewise influenced, as in the case of hydrogen and chlorine. Among other photo-chemical changes, the oxidation of guaiacum resin, which turns

blue under the influence of light, may be mentioned. Some bodies again are not influenced by light when isolated, but only when mixed; as is the case with nitrate of uranium in alcohol (but not in water), bichromate of potash, and gelatine. Phosphorus is modified by light, as are also some kinds of glass. Berthelot has pointed out that the chemical phenomena brought about by light are complex in origin, but he is of opinion that most of them, if not all, are exothermic-that is, that light plays the part of a mere inciter, without losing any of its energy. On the other hand, in so-called endothermic photo-chemical phenomena, light energy is transformed into chemical energy.

This much being stated by way of preliminary, the influence of light on living organisms can now be considered, although it is not possible in this place to describe in detail the numerous experiments that have been made in this direction. The stimulating action of the sun's rays on plant-life is well known. Priestley, the great English natural philosopher and pioneer of modern chemistry (1733-1804), showed that oxygen (or 'dephlogisticated air,' as he called it) was given off by green leaves under the influence of sunlight. Moleschott, the physiologist, also found that frogs give off more carbonic acid under the influence of light than in the dark.

Light, by influencing the green colouring matter of plants (chlorophyll), splits up the carbonic acid of the air into carbon and oxygen. By the combination of the carbon with water, starch is built up by the plant. The oxygen given off serves, inter alia, for the respiratory purposes of animals. In this way is the cycle of life carried on. 'Rien ne se perd, rien ne se crée,' as Lavoisier put it. Engelmann long ago showed that when the amoeba-like rhizopod, Pelomyxa palustris, is suddenly illuminated, the creeping elongated protoplasmic body at once assumes a spherical shape and becomes motionless; and he subsequently discovered a bacterium which is extremely sensitive to the effects of light-rays. This mobile organism, which he named Bacterium photometricum, is furnished with a flagellum or whip-like appendage by means of which it is propelled. When exposed to light, this bacterium moves about actively in the field of the microscope; but, if it is brought into darkness, the motion gradually

ceases, to return when the animal is again exposed to light. Further, this investigator was able to show that it was the orange and the ultra-red rays of the spectrum which especially exert this influence. In the foregoing experiments, the effects of light-stimulation are negative (as in Pelomyxa) or positive (as in B. photometricum). The phenomenon has received the name of 'phototaxis.'

In connexion with the present subject, the experiments of Verworn with a ciliated infusorium, Pleuronema chrysalis, should not be omitted. These small organisms exhibit curious jumping movements when exposed to light. It was shown that these movements are not a thermal effect of ordinary daylight, but are due chiefly to the action of the blue and violet rays of the spectrum, that is, the rays which exert the least thermal effect. The same result could be obtained by heat-rays; but ordinary daylight is not sufficient, a considerable intensity of sunlight being requisite. Engelmann again found that the motion of those remarkable microscopical organisms, diatoms (Diatomaceæ, an order of unicellular algæ), can be influenced by light. The movements of these organisms are arrested when they are placed in a dark chamber and oxygen excluded, to return again when light acted upon them. Absence of oxygen leads to cessation of movement; but the diatoms exposed to light again split up the carbonic acid into oxygen and carbon by means of their yellow colouring matter, which is allied to chlorophyll. If space allowed, we might mention a number of other experiments which have brought out the importance of the blue, violet, and ultra-violet rays in the production of excito-motor phenomena.

We may now deal with the effects of light on bacteria. In this country, Downes and Blunt were the first to carry out experiments with solar light in this direction (1877); and, although these experiments were somewhat crude and open to objections, they called attention to the bactericidal power of light. As a result of their experiments, these investigators considered that the action of light on bacteria was mainly due to the chemical or actinic portion of the spectrum. Duclaux insisted on the influence of temperature and of the nutrient medium employed for growing the bacteria. Arloing and Roux, and also Nocard and Strauss, took up the subject in

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