128 RADIO-ACTIVITY 



Several investigators have reported results to show that the 

 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 de- 

 struction 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 the emanation from radium. That 

 the action is electrical is borne out by the antagonism between 

 a radiation and ft 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. 81). 

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

 by exposure to radium. Especially sensitive are the sexual cells. 

 Spermatozoids of sea urchins are enfeebled and killed, as are also 

 the gametes of the grasshopper by exposure to radium sufficiently 

 weak to have no action on other cellular units of the testicles. The 

 action is similar to exposure to cold. Radium causes an immediate 

 decrease in the total number of white cells in the blood (Chap. XV.). 

 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 | 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 (p. 9), matter 

 exposed to radio-active elements should develop some protective 

 mechanism against the action of the rays. Becquerel noticed 

 that f$ 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. 



