164 RADIO-ACTIVITY 



growth-promoting substance in yeast may be partially inactivated 

 by exposure to radium emanation. It is probable that the 

 therapeutic effect of radium treatment may be due to this destruc- 

 tion of the growth-promoting substance. It has been known 

 for long that radium rays have a destructive effect on colloidal 

 solutions, due probably to a disturbance of their electrical state. 

 Globulin and vitellin are coagulated and lecithin suspensions are 

 decomposed on exposure to radium emanation. That the action 

 is electrical is borne out by the antagonism between a radiation 

 and ^ radiation. Either of them prevent bacterial growth in 

 agar cultures, but the simultaneous application of both kinds of 

 rays is ineffective (cf. antagonism of colloids, etc., p. 96). Of 

 course, normal as well as pathological tissue may be damaged by 

 exposure to radium. The action is similar to exposure to cold. 

 Radium causes an immediate decrease in the total number of white 

 cells in the blood (Chap. XVI.). This result is probably due to 

 inhibition of the formation of the leucocytes rather than to the 

 destruction of already formed cells. The greatest decrease occurs 

 from I to 6 hours after application of the radium. Within 24 hours 

 a normal concentration of white cells may be observed. 



By the operation of Le Chatelier's principle (q.v.), matter 

 exposed to radio-active elements should develop some protective 

 mechanism against the action of the rays. Becquerel noticed 

 that /3 rays changed yellow phosphorus into its red form, which is 

 not acted on by the rays. We have already mentioned that the 

 fertilisation membrane of nereis is thickened where exposed to 

 radium. Some observers find that the presence of chlorophyll 

 is protective. Others deny this. 



Ultra-Violet Rays. 



The physician is interested in radiant energy of this type because 

 of its lethal influence on pathological growths and on bacteria. 

 Ultra-violet rays, or lights like the Simpson Light, which emit a 

 large proportion of ultra-violet rays, have been employed as 

 germicides in surface wounds. The penetrating power of these 

 rays is slight, and, therefore, they can have little effect on deep- 

 lying structures. 



The tissues may, however, be made sensitive to rays of some- 

 what longer wave-length by administering coloured substances 

 which act as sensitisers. For example, haematoporphyrin, an 

 iron-free disintegration product of haemoglobin, so sensitises the 

 tissues that ordinary daylight produces similar effects to idtra- 

 violet light. These effects are mainly psychological and photo- 

 chemical. The latter action has been carefully investigated, the 



