Saleeby says: "That a properly aired and lighted skin becomes a velvety, supple, copper coloured tissue, absolutely immune from anything of the nature of pimples or acne, incapable of being vaccinated, (meaning its resistance to infection is greatly increased--Author), and its little hairs usually show considerable development. When the visitor touches such a skin in the cool air, he is surprised to find it quite warm. The sun was not shining when I did so first, and the patient was, of course, perfectly nude except for a loin cloth. Evidently plenty of heat was somehow being produced in that little body, with so large a surface to cool, relatively to its mass."

The increased resistance to infection and to "disease" influences seen in the skin extends also to the internal organs. Dr. TraLl declared that "nearly all forms of disease are more severe and unmanageable in low, dark apartments." With an insufficiency of light, the blood fibrin and the red corpuscles become diminished in quantity. The serum or watery portion of the blood is increased, inducing leukemia, a condition characterized by a great increase in the number of white blood corpuscles. A total exclusion of sun-light induces the more severe forms of anemia, a fact emphasized by Trall, originating from the impoverished and disordered state of the blood.

Cancer is less prevalent in the sunny regions of the earth. Inhabitants of southern mountain slopes are stronger and healthier than those living on the northern sides. Tenement house districts, in the large cities, to which sunlight has no access, have the greatest infant mortality and are the chief breeding places for rickets and tuberculosis. Pneumonia is most prevalent during dark, cloudy weather. Trall declared that "diseases of all kinds, from the most trifling toothache, quincy, or rheumatism, to the severest attack of fever, scrofula, or consumption, are much less manageable in low, dark apartments. And it is notorious that during the prevalence of epidemics, as the cholera, the shaded side of a narrow street invariably exhibits the greatest ratio of fatal cases."

Dr. Carl Sonne experimented with the light bath on guinea pigs to determine its action on diphtheria toxin in the body. He, of course, employed experimental "diphtheria," that is, cultures of the supposed diphtheria bacillus. His findings, however, are of value for the introduction of this material into the body means the introduction of powerful toxins. He found that the bath tends to the rapid destruction of the toxin. Saleeby describes the results thus: "The destruction in the course of a single light bath lasting two hours, without the production of any fever (rise in the general body temperature) is as great as that caused by a fever of 40 degrees C., lasting several days and nights. The possible significance of this remarkable result for the treatment of such disease as diphtheria will be evident to the reader.

The germicidal power of sunlight is well known. It is the greatest of all disinfectants and antiseptics. Drs. Trall and Taylor both emphasized its powers in these directions. However, even in allopathic circles, where the germ theory is strongest, the idea is growing that light is less valuable in killing the germ than in raising the body's resistance to it.

In 1876 Downes and Blunt discovered the bactericidal power of violet light, although sunshine had long been used to disinfect "contagious" garments. There is now much effort to show that sunlight works by killing pathogenic bacteria and Finsen has attempted the treatment of lupus with artificial light.

However, sunlight has proved most valuable in rickets, anemia and a few other conditions in which bacteria are not assumed to act as etiological factors, while investigations have shown that the rays of short wave-lengths employed by Finsen have such feeble penetrating power that one bacterium shields another and that it is practically impossible that many of the well-entrenched "bugs" can be reached and destroyed by the rays.

Drs. Hill and Eidinow attempted to show that the ultra-violet rays cause the production of bactericidal substances. Dr. Eidinow found that sufficient ultra-violet insolation to cause erythema will increase the bactericidal power of the blood and it is now claimed that the Finsen lamp is more effective in the treatment of lupus if supplemented by general ultra-violet radiation.