Biological Effects of Penetrating Radiations 89 



of the radiation shortens. Large doses of highly penetrating 

 radiations can now be given to a deep-seated tumor with 

 comparative safety to the skin. But with this decrease in 

 absorption of radiation on the skin, there is an increase in the 

 energy absorbed in the deeper parts of the body, and this, in 

 turn, indirectly affects the "treated area" by the production of 

 adverse constitutional disturbances. This question of body dose 

 was raised in 1938, when the constitutional effects of teleradium 

 therapy were under consideration at the Radium Beam Therapy 

 Research, London. ^^'^ It has been systematically developed by 

 Mayneord in a series of publications. For measuring this radia- 

 tion he suggests a unit to be called the "gram-rontgen," which 

 may be defined as the energy absorbed in 1 gram of tissue irradi- 

 ated with one rontgen.®'^ 



TABLE I 



Illustrating Biological Response to a Variety of Radiation Dosiis 



No. Dose in r Biological Response 



1 10"^ "Safety" limit of exposure for radiographers, etc., 



per second ^ 



2 0.175 Dose received per day by attendants using a 4- 



gram radium unit ^ 



3 0.25 "Safety" limit of exposure per day (7-hour day)-^ 



4 0.5-1.0 Front of fluorescent screen during examination 



of patient ^2 



5 '1.0 Palpating hand of operator using fluorescent 



screen every 10 min.^^ 

 "Safety" limit of exposure per day (5-day week) 5 

 Threshold for mitotic effect in grasshopper '^ 

 Received by diagnostician making complete radio- 

 graphic study of gastro-intestinal tract (see 

 No. 13)68 

 9 15 To either gamete produces developmental abnor- 



malities in 5% of individuals (frog) (see No. 

 18)57 



10 34 Threshold for mitotic effect in chick fibroblasts 



(cf. No. 7)1^9 



11 40 Alteration in ultraviolet absorption in cell-cyto- 



plasm 



