1912] on Vital Effects of Radium and other Rays. 297 



this method is that it can be used at the very time that the x-Ya,y& 

 are being appUed to the patient, so that whatever variations may take 

 place in the output of the tube all of them are recorded, so to speak, 

 by the tint produced in the pastille. With these safeguards the 

 ;r-rays, applied for medical purposes, may now be said to be entirely 

 free from all risk to the patient. 



Fenetrahiliiy. — Unlike the violet and ultra-violet rays, the a'-rays 

 penetrate deeply — can, in fact, pass right through the body easily — 

 but they vary in penetrability according to the condition of the 

 Crookes tube. The tube may be in a condition which is called 

 " soft " or " low," so that the rays produced will cast a shadow of 

 the hand without showing the bones at all, or it may be " hard " or 

 " high," so that the rays, passing easily through, make the bones 

 look quite pale on the fluorescent screen ; and there are all inter- 

 mediate stages. 



I have already said that the opacity of a substance to the a;-rays 

 is in proportion to the atomic weight of that particular substance. 

 Recently Dr. Lindemann has made a glass of light atomic weight 

 which, when put in the tube as a window, allows many rays of very low 

 penetration, which in ordinary tubes are prevented from escaping 

 beyond the glass, to pass through. Already very valuable therapeutic 

 results have been obtained by the use of these tubes. 



[Show Lindemann tube.] 



X-ray Effects on Cells.— T]iq most striking and general vital 

 effect of the «-rays is to be witnessed upon young and growing cells. 

 Guinea-pigs a day or two old are killed with great rapidity, and 

 before any visible effects of radiation in the shape of burning make 

 their appearance. The adult animal, on the other hand, shows a 

 greater capacity for resistance. In a recent communication to the 

 Royal Society, J. F. Gaskell, who has studied the action of the ;<-rays 

 on the developing chick, stated that he had found this action to be 

 confined to a lowering of the mitotic (or cell-multiplying power) of 

 the growing tissues. If this diminution were not too great complete 

 recovery occurred, and the chicks were hatched out at the usual time, 

 but if it fell below a certain degree, all further development was 

 arrested. On the same principle of attacking young and growing 

 cells, the a;-rays injure the hair follicles and bring about the fall of 

 the hair — -a convenient method of epilation now employed with 

 signal success in the treatment of ringworm in children. Prolonged 

 exposure to the rays will produce total baldness. The sweat glands 

 can also be destroyed in the same manner. The action of x-rays 

 upon the blood is limited chiefly to the white blood corpuscles, the 

 red Ijlood corpuscles being very resistant. The central nervous 

 system also, fortunately, has great resisting capacity. 



Latent Period. — When the skin is exposed to the x"-rays, no 



