[ 491 ] 



XXXVII. 



RADIO-THERAPY: ITS SCIENTIFIC BASIS AND ITS 

 TEACHING.' 



By J. JOLY, Sc.D., F.KS. 



[Read March 23. Published Apkil 29, 1915.] 



The recent discovery that X rays and y rays can be defracted into spectra 

 by the natural grating contained in the orderly structure of crystals, sets at 

 rest the question as to the nature of these radiations. They are of the same 

 nature as light-waves, but of very much higher frequency — from 10,000 to 

 100,000 times as Jiigli.^ 



Such rapid vibrations do not evoke the sensations of sight. Our tissues 

 are, indeed, to a considerable degree, transparent to them ; the power of 

 penetration increasing with the frequency or as the wave-length diminishes. 

 Whereas light- waves are rapidly absorbed within a few millimetres of the 

 surface of the skin, these rays can penetrate deeply ; some of the highest 

 frequency even passing right through the body. 



The certitude of the identity of these three classes of radiation leads to 

 issues of much importance to medical science. For medicine had for many 

 years been invoking the aid of the mysterious X and j rays without in the 

 least knowing what these agents were. It now turns out that they are 

 physically identical with light. This fact secure, medical science is made 

 heir to the discoveries of photo-electric science. It is for the piiysician now 

 to enter into his inheritance, and to see what it teaches him as to the 

 interpretation of his past results and as to openings for future advance. 

 I shall restate the leading facts of photo-electric science. 



In 1887 Hertz noticed that the passage of an electric spark between the 

 terminals of an induction coil was much facilitated by the discharge of 

 another spark in its neighbourhood. He showed that the light from the 

 spark was the agent which promoted the discharge. Ebert, the ensuing year, 



' Based on a paper read to the members of the Dublin Clinical Club on March 16, 1915. 

 - The wafe-lengtbs of these various rays are of the following orders: — light, 10"= cms.; 

 X rays, 10-' cms. ; 7 rays, 10"' cms. 



SCIENT. PKOC. B.D.S., VOL. XIV., NO. XXXVII. ^ 4 1 



DEC 14 1916 



