CHAPTER XIV 



X RAYS AND X IRRADIATION 



John \V . (JoweN, luwa Slate Culleye 



A . Sources of X-Ray Radiation 453 



B . Dosimetry 456 



1 . Units of Measurement 456 



2. The Depth-Dose Problem 458 



3. Monochromatic X Radiation 461 



C. Theories of X-Ray Actions 462 



1 . The "Point-Heat" Concept 462 



2. The Sensitive Volume Concept 464 



3 . Current Ionization Concepts 465 



D. Materials for Study of Irradiation Effects 468 



E. Types of Data Accruing from X Irradiation of Biological Ma- 



terials 470 



F. Methods of Measuring Biological Effects of X Rays 473 



1 . Virus Materials 473 



2 . Drosophila Genetics 476 



3. Cytological Methods 479 



4. Bacterial Mutations 480 



5. Embryological Studies 482 



G . Statistical Treatment of Radiation Data 484 



H . Interpretation of Radiation Effects 486 



References 488 



Three broad categories of investigators are interested in the bio- 

 logical effects of X rays. First are those who wish to photograph oi- 

 register on fluorescent screens abnormal structures deep within the 

 tissues. In this manner abnormalities are brought to view and suit- 

 able action taken. The second group is interested in the effect of 

 radiant energy on abnormal growths within the organisms. It 

 seemed possible that, through differential absorption of radiant 

 energy, abnormal growths could be immobilized, and eventually 

 regress and be replaced by normal tissue. Some success in this direc- 

 tion has led to a broad study of X-ray effects. The third group is 



451 



