﻿i 9 i6] BOVIE- SCHUMANN RAYS .7 



cells, including those which contain the pigment. The skin, there- 

 fore, becomes more transparent with each successive exposure, and 

 hence there is a continual increase in the penetration of the light. 



Experiments were made with light sources which emit a rela- 

 tively greater amount of light in the extreme ultra-violet than is 

 emitted by the carbon arc; but it was found that there was no in- 

 crease in the therapeutic effects, while there was an undesirable 

 increase in the amount of destruction of the epidermal cells (29). 



The therapeutically effective rays are those which have wave 

 lengths between 4000 and 3220 Angstrom units. These rays, after 

 passing through a layer of skin 4 mm. thick, have a strong destruc- 

 tive action upon bacteria. Light of wave lengths shorter than 

 3220 Angstrom units has no action upon bacteria which lie beneath 

 the surface of the skin (23). 



The light from the carbon arc is passed through a concentration 

 apparatus provided with condensing lenses of quartz, and also with 

 water niters for absorbing the heat rays. The area to be treated 

 is made as nearly bloodless as possible and is exposed to the light 

 for 1 hr. and 15 min. at intervals of 1-3 days. The local anemia is 

 produced by pressing the area during the exposure with a quartz 

 lens. In certain skin diseases, notably Lupus vulgaris, the light 

 treatment is so successful that out of 350 cases treated previous to 

 1899 there were none which did not show improvement, and only 

 5 which were not cured. The result is so certain and so constant 

 that there is every reason to doubt the accuracy of the diagnosis 

 of Lupus vulgaris when the method fails. 



Besides developing " positive phototherapy" to a high degree of 

 perfection, the studies carried on at the Finsen Institute contributed 

 a large amount of information to our general knowledge of the 

 destructive action of light. The experiments of previous investi- 

 gators were carefully repeated and their significance was critically 

 discussed, while extended researches were made into new fields. 



As pointed out by Lobel long ago, the biological effects of expo- 

 sure to light are the result of photochemical action. Hence if we 

 are to obtain a clear understanding of the biological action of ultra- 

 violet light, it will be necessary to consider some of the characteris- 

 tics of photochemical reactions. 



