294 Sir James Mackenzie Davidson [Feb. 2, 



X-ray Burns. — The burning effect of a?-rays upon the skin was 

 in a certain sense discovered accidentally. The early tubes used for 

 the production of a;-rays were rather imperfect, and therefore very 

 long exposures had to be given in order to obtain radiographs. In 

 this way many severe burns were produced upon unfortunate patients. 

 The operators themselves also began to suffer ; and in this country 

 we were all shocked by the untimely death of Dr. Blacker, of St. 

 Thomas's Hospital, who was a most enthusiastic pioneer in a;-ray 

 investigation, and whose death was directly due to the destructive 

 effect of x-vsijs upon the tissues. It was a sad instance of a young 

 and promising life being cut short by this new, and, as it has ulti- 

 mately proved, beneficial agent, before we had learned to guard 

 against its dangers. 



It is worthy of note that most, if not all, ;c-ray burns produced 

 in operators began in the uncovered parts of their skin, such as the 

 hands and face. A good deal of doubt still exists as to whether the 

 primary a;-rays alone are responsible for these manifestations. Having 

 suffered from chronic x-raj burn in my hands, especially in my right 

 hand, it seemed to me rather remarkable that the area of trouble at 

 the back of the hand should end sharply at a line corresponding to 

 the usual position of the coat cuff, for cloth is quite transparent to 

 the x-TSkjH ; and the adjacent parts of the skin beneath the sleeve 

 were, in my own case, equally exposed with the uncovered hand itself. 



Secondary Rays. — Many views have been brought forward to 

 explain the causation of some a;-ray burns, without any very definite 

 results, and it appears probable that the secondary or indirect rays 

 given off from the surface of the glass may be, if not in some cases 

 the primary factors, certainly largely contributory to these superficial 

 skin burns. 



The existence of these secondary and less penetrating rays can 

 be very readily demonstrated by exciting a Crookes tube in the 

 ordinary way, and suspending opposite the point from which the 

 primary rays emerge a mass of lead, through which no primary or 

 direct ic-rays could possibly penetrate. Naturally, a shadow of this 

 lead is cast by the a;-rays coming from a fine point in the anode, and 

 which we may at present call the primary rays ; but within this 

 eclipsed area we get shadows caused by other rays, and when these 

 are traced they can be shown to be produced on the glass of the 

 tube, which fluoresces green. These rays are much more richly 

 produced in what is called a high or hard tube. I demonstrated 

 them in my lecture here on April 25, l'J02. 



Mr. Campl)ell Swinton alludes to the existence of these rays in 

 a paper on " The Source of the Rontgen Rays in Focus Tubes," 

 published in 1898. He describes them as secondary rays from the 

 green fluorescing glass of the a;-ray tul)e, and has taken pin-hole 

 photographs of them. 



As a further confirmation of the possibly vital effect of these 



