308 BIOLOGICAL EFFECTS OF RADIATION 



of heavy ions such as would result from the breaking up of molecules 

 rather than from the emission of electrons. 



EFFECT OF RADIATION ON SUSPENSOIDS 



Before taking up the effect of radiation on proteins it is well to sum- 

 marize briefly the effect on lyophobe suspensoids, and metallic hydroxides. 

 Crowther and Fairbrother (12) radiated Bredig solutions of iron and 

 copper which are positively charged suspensoids and a Bredig solution 

 of silver and colloidal gold, which are negatively charged, with X-rays 

 from a molybdenum tube. The colloidal copper precipitated on radiation 

 and the iron was more easily precipitated after radiation by potassium 

 chloride. The negatively charged colloidal silver and gold, however, 

 became more dispersed and more stable after radiation. After exposure 

 to X-rays, colloidal gold did not precipitate on boiling. Crowther found 

 that the effect of beta rays on a Bredig solution of copper was exactly 

 the same as that of X-rays. They concluded from these experiments 

 that X-rays and radium rays coagulate positively charged suspensoids, or 

 make them less stable, whereas they disperse negatively charged sus- 

 pensoids and make them more stable. 



Nordenson (41), on the other hand, found that two types of colloidal 

 gold, prepared by different methods, one giving positively charged 

 particles and the other negatively charged particles, showed aggregation 

 under ultra-violet radiation and that there was a similar though less 

 marked effect with beta rays. He concluded that radiation has a slow 

 coagulating effect on metallic colloids like that of weak electrolytes, 

 and that the effect is independent of the charge on the particle. The 

 aggregation was accompanied by a decrease in the charge, whether posi- 

 tive or negative, which he attributed to the absorption of H+ or 0H~ ions 

 formed in the solvent by the radiation. 



Fairbrother (16) and Crowther (11) studied the effect of X-rays 

 and the beta rays of radium on eerie hydroxide. This solution shows 

 changes in viscosity on radiation. When exposed in low concentrations 

 the viscosity decreases to a minimum and then increases with final 

 setting to a gel. In sols of higher concentration there is such a rapid 

 gel formation that the initial decrease in viscosity is masked. If the sol 

 is radiated to the point of minimum viscosity, it will then set without 

 further radiation, although very slowly, whereas it sets rapidly with con- 

 tinued radiation. The initial decrease in viscosity is supposed to be due 

 to discharge of the positively charged colloid, and the subsequent rise in 

 viscosity to aggregation of the discharged colloidal particles. In compar- 

 ing the effect of beta rays and X-rays there was numerical equivalence 

 between the effect of the two types of radiation as far as the discharge of 

 the particles and decrease in viscosity were concerned, but the aggregation 

 and rise in viscosity were more rapid under beta radiation. He found, 



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