February 29, 191 2] 



NATURE 



601 



■spectrum was well brought out in the course of an experi- 

 ment in which, tiie spectrum having been produced upon 

 *he screen, a strip of bromide paper was stretched across 

 it so as to receive the length of the spectrum, and this on 

 being developed and fixed was shown to have darkened 

 very considerably at the blue and violent portion, while the 

 red end of the spectrum was practically white paper. The 

 more ready absorption of these blue and violet rays, known 

 to everyone who has looked at the reddened disc of the 

 sun through a somewhat dense fog, was further illustrated 

 by placing a glass cell in front of the lantern and filling 

 it with hypo solution to which some hydrochloric acid was 

 added. Ultimately, only the red waves were able to pene- 

 trate. The lecturer further pointed out that the blue 

 colour was the last to be seen at the close of day ; 

 that when a person had his sight temporarily impaired 

 by over-indulgence in tobacco he lost the perception of red 

 and green in the centre of his field of vision, but very 

 rarely lost the perception of blue ; and that in cases of 

 blindness coming on gradually from wasting of the optic 

 nerve, blue was the last colour to go. 



After reviewing the Finsen light treatment, which was 

 based upon the fact that the most effective rays, physio- 

 logically speaking, were those of the violet and ultra-violet, 

 and the superseding of the arc by a quartz mercury vapour 

 lamp for the production of active violet light in large 

 quantities, the lecturer turned to the X-rays, and spoke of 

 the early X-ray burns sustained by operators, paying a 

 tribute to Dr. Blacker, of St. Thomas's Hospital, one of 

 the first martyrs in radiology. Sir James proceeded : — 



"It is worthy of note that most, if not a'l. X-ray burns 

 produces in operators began in the uncovered parts of 

 their skin, such as the hands and face. A good deal of 

 loubt still exists as to whether the primary X-rays alone 

 are responsible for these manifestations. Having suffered 

 from chronic X-ray burns in my hands, especially 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, of course, is quite transparent to the X-rays, 

 and the adjacent parts of the skin beneath the sleeve were 

 in mv own case equally exposed with the uncovered hand 

 itself. 



" Many views have been put forward to explain the 

 causation of certain of the X-ray burns, but it appears 

 probable that the secondary or indirect rays given ofif from 

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

 primary factors, certainly largely contributory to these 

 superficial skin burns. As a further confirmation of the 

 possibly vital efi'ect of these rays upon the skin, I may 

 mention that Freund, of Vienna, found that a tube so 

 high as to give no fluorescence on the screen caused the 

 hair to fall out, and also that, with a tube having the 

 electric current passed in the reverse direction so as to 

 produce only very weak primary X-rays, similar results 

 were obtained. It would be interesting to construct a 

 tube so as to employ for therapeutic purposes these 

 secondary rays alone." 



The lecturer demonstrated the existence of these 

 secondary and less penetrating rays 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 X-rays could possibly 

 penetrate. Naturally, a shadow of the lead was cast by 

 the X-rays coming from a fine point in the anode — the 

 X-rays which may, for the present, be called the primary 

 rays — but within this eclipsed area he obtained shadows 

 caused by other rays, and when these were traced they 

 were shown to be produced on the glass of the tube, which 

 fluoresced green. These rays, he found, were more richly 

 jjroduced in what was called a " high " or " hard " tube. 

 On making comparative measurements of the rays by 

 means of the electroscope, he found that with a high tube 

 ^'iving very penetrative rays, if the action of the primary 

 rays were taken as i, the action of the secondary rays 

 would be \, and that with a low tube giving X-rays of 

 a low order of penetrability, if the primary ravs were 

 again taken as i, the secondary rays would be one- 

 seventh. 



NO. 2209, VOL. 88] 



The work done upon these secondary rays from the 

 physical side is comparatively slight. Mr. Campbell 

 Swinton alludes to their existence in a paper published in 

 1898, when he describes them as secondary rays from the 

 green fluorescing glass of the X-ray tube ; and at a some- 

 what earlier date Prof. Silvanus Thompson showed that 

 the kathode stream, after impinging upon the target and 

 thus giving rise to the main beam of X-rays, was reflected 

 and impinged upon the glass walls of the tube, thus 

 causing a green fluorescence. He called these reflected 

 kathode rays " para-kathodic. " "Whether they produce 

 X-rays upon this second impact or not does not appear to 

 have been proved," said Sir James Davidson in concluding 

 this portion of his lecture, " but as Barkla and Sadler 

 and others have demonstrated that X-rays outside the tube, 

 impinging upon solid matter, give rise to secondary rays, 

 it seems certain that the X-rays, in passing through the 

 walls of the tube in which they are generated, must give 

 rise to secondary X-rays, and it may well be the case that 

 the green fluorescence of the glass of an X-ray tube gives 

 us two sets of X-rays — one produced by the primary 

 X-rays in their impact on passing through it, and the 

 other produced possibly by reflected kathodal rays. Be 

 that as it may — and it is a matter for the physicist — I feel 

 sure that their physiological action upon the skin must be 

 considerable, especially as they are much more readily 

 absorbed than the primary X-rays." 



Discussing the methods of protection against X-ray 

 burns, the lecturer said that many years ago he made an 

 experiment in which a Crookes tube was completely 

 buried in a large quantity of red lead contained in a box, 

 and when this was excited in a dark-room the fluorescent 

 screen showed that no X-rays at all were able to penetrate. 

 Then a small opening was made by scooping away the 

 red lead until the primary rays got through, together with 

 only a very few of the secondary rays from the small area 

 of glass opposite the orifice. This was the most effective 

 means of screening everybody from the rays except the 

 individual under observation, but it was highly incon- 

 venient, the apparatus being diflficult to handle, especially 

 when a fresh tube had to be embedded. Therefore a box 

 was constructed, lined with a mixture of red and white 

 lead, and a small hole was cut in it for the emission of 

 the rays. Some such method, he added, was now gener- 

 ally adopted, and was most important for the protection 

 of the workers. The lining of the fluorescent screen with 

 thick lead-glass, and the Sabouraud pastille method of 

 dosage, with other safeguards, rendered the X-rays, as 

 applied for medical purposes, practically free from risk to 

 operator and patient alike. 



The lecturer then proceeded to describe the effects of 

 X-rays upon cell-life, pointing out their radical influence 

 upon the young and growing tissues. On the principle of 

 attacking the young and growing cells, the X-rays injured 

 the hair follicles and brought about the fall of the hair. 

 The sweat glands could be destroyed in the same manner. 

 The action of the X-rays upon the blood was limited chiefly 

 to the white blood corpuscles, the red blood corpuscles 

 being very resistant. The central nervous system also, 

 fortunately, had great resisting capacity. The most 

 sensitive of all the tissues were the lymphoid tissues gener- 

 ally, especially the spleen, which shrank and became 

 strongly pigmented under the attack of the radiation. 

 Indeed, in certain diseased conditions of the spleen the 

 X-rays had been used with marked success. In malignant 

 tumours, while the X-ray method might be of service in 

 checking the rapidity of the growth, it could not be looked 

 upon as a method of cure, although after the removal of 

 such growths by operation the application of the rays 

 to the involved area might assist in destroying any of the 

 malignant cells which the surgeon's knife had missed, and 

 thus preventing redevelopment. As the technique of the 

 X-rays improved, the field of their utility in therapeutics 

 would be gradually extended. 



Next in order to the X-rays, historically, came radium.. 

 The events which led up to the discovery of this substance 

 were summarised, and the physical properties of radium 

 were described. The process of the disintegration of the 

 radium atom, through which was evolved the radiant 

 encrg\ of such service in medicine, was admirably illus 



