. Radiotherapy and phototherapy : including radium and high-frequency currents, their medical and surgical applications in diagnosis and treatment ; for students and practitioners . gle of total reflec-tion has its vertex. It will be seen that there is reflectionof light at every point, and that the amount of this increasesas we get farther from the centre until the point is reachedwhere the amount of light that enters the lens is smallerthan that reflected, and so on until there comes a time whenno light enters the lens at all. This limits the availableangular aperture of lenses to something
. Radiotherapy and phototherapy : including radium and high-frequency currents, their medical and surgical applications in diagnosis and treatment ; for students and practitioners . gle of total reflec-tion has its vertex. It will be seen that there is reflectionof light at every point, and that the amount of this increasesas we get farther from the centre until the point is reachedwhere the amount of light that enters the lens is smallerthan that reflected, and so on until there comes a time whenno light enters the lens at all. This limits the availableangular aperture of lenses to something under 73 degreesfor ordinary glass. PHOTOTHERAPEUTIC APPARATUS 473 Lamps. Because of the great expense, size, difficulties inmaintaining, and in the United States for the further reasonthat there is comparatively little lupus to treat, there hasarisen a demand for inexpensive appliances. Many of thenewer lamps have limited actinic possibilities, and somehave been used from which little or no actinic rays couldbe expected. The original arc lamp represented 50 to 60amperes, and from the light there radiated a number oftelescopic tubes cooled by their containing water. Fig. Illustrating critical angle of lenses. Illustrations of the smaller varieties of lamp and methodsof easy or self application are shown in Figs. 93 and 94. The modified Gorl, of flat model, might be bound on, asshown, or the regular oblong form can be held with orwithout a handle by the patient. The limited success attending the use of various apparatusis largely due to attempts to shorten the sittings. Finsen finds that to obtain the best results lamps requirea current of 60 to 80 amperes. With such lamps the sameeftects will be accomplished in twenty to twenty-five seconds,which with a 40-ampere lamp require four to five minutes. 474 ACTING THERA P Y Fig. 93.
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