380 BIOLOGICAL EFFECTS OF RADIATION 



the "bodies" concerned may just as well be utterly different, for all that 

 we really know. 



c. Experiments with other than ultra-violet radiation are for the most 

 part so scattering that intercomparison of different substances (under 

 h above) or different types of radiation is difficult. This is especially 

 true because of the meagerness of description of the physical nature 

 of the radiation, the absorbing properties of the irradiated system, and, 

 in the region of X-rays and radioactive rays, the multiplicity of inde- 

 pendently variable units, none of which is very satisfactory in practice. 

 One can say with a good deal of confidence, however, that the properties 

 under consideration are little if at all affected by visible light, except when 



o 



photodynamic sensitizers are used; that from about X 3000 to 2800 A on, 

 lability increases with decreasing wave-length until excessive absorption 

 makes experiment impracticable, while X-rays and gamma rays are 

 relatively ineffective, and alpha rays effective. Much of this appears to 

 be a question of how effectively the radiation is absorbed: there is good 

 reason to believe that if absorbed the energy of any quantum greater 



o 



than that corresponding to X ~ 3000 A is utilized, and that the change 

 induced is very closely proportional to the energy absorbed by the sub- 

 stances whose chemical change leads to inactivation. 



d. If this be true, the mechanisms involved may well be quite similar 

 except for electromagnetic radiation of X > 3000 A, approximately. 

 Since at longer wave-lengths oxygen is required, while with larger 

 quantum energy it may perhaps be made available by irradiation in the 

 absence of free oxygen, it seems not improbable that inactivation of toxins 

 and immune bodies by radiation may be due to oxidation following 

 primary activation of oxygen. One must nevertheless keep in mind the 

 process of protein denaturation and the ensuing colloidal changes, which, 

 however, seem to be rather slower than the changes in toxins and immune 

 bodies. Electrical discharge of colloidal particles by alpha and beta rays 

 has also been suggested as a possible mechanism. Reduction processes 

 have also been suggested. The last two hypotheses now seem relatively 

 improbable, and oxidation the most probable. No one type of reaction 

 may account for all or even any one of the changes described. 



e. Irradiation tells us little about the chemical and physical nature 

 of toxins and immune bodies. It is easy to conclude from analogy that 

 they are single molecular species, that they possess such and such chemical 

 nature or groupings; but analogy is not proof. The irradiation of alexin 

 has led to suggestive hypotheses as to its dual nature: lytic substance 

 with special dependence on the physicochemical state of serum proteins 

 (globulins in particular) (see page 363). This amplifies the more 

 generally accepted view that alexin is the latter only. Future work 

 along physicochemical lines, including the better planned use of irradia- 

 tion as a tool, should show whether or not this suggestion has worth. 



