Effects of X-Rays and Atomic Radiations on Living Cells 63 



by natural sources. In addition, we may receive radiations from (3) 

 artificial sources of radiations such as X-rays used for medical exami- 

 nations and radioactive paints used on watch dials; (4) radioactivity 

 derived from the 'fallout' from the explosion of atomic bombs and of 

 thermonuclear weapons. A very careful study of these effects has 

 been made by government committees in both the United Kingdom 

 and in the United States of America. 



It is estimated that from natural sources of radiation including 

 cosmic rays and naturally occurring radioactive substances, an indi- 

 vidual in the United Kingdom will receive a total dose in the repro- 

 ductive organs of about three roentgens during a period of thirty 

 years, which is taken as the average reproductive period. This appears 

 to be less than the amount of exposure which would be required to 

 double the natural spontaneous rate at which some mutations occur. 

 The average dose received by the reproductive organs from the diag- 

 nostic use of X-rays is estimated to be about 20 per cent of the dose 

 from natural sources. The dose of radiation which individuals are 

 likely to receive from the radioactive 'fallout' from atomic or thermo- 

 nuclear explosions is comparatively small and even if continued in- 

 definitely at the same rate as during the last few years, would only 

 amount to one per cent of the radiation from natural sources. 



To find the actual chemical changes which are responsible for the 

 biological effects of radiation much work has been done on the effects 

 of the radiations on nucleic acids. It is only necessary to say here that 

 the radiations do bring about numerous different kinds of chemical 

 changes. They not only destroy the bases on which, as we have seen, 

 the genetic properties ultimately depend; but they are also capable of 

 breaking a dna particle into two or more parts. There is little doubt 

 that these chemical changes are sufficient to give rise to the observed 

 effects of the radiations on the chromosome and consequently to the 

 genetic effects which they produce. 



If the genes can be damaged by chemical reactions which pene- 

 trating radiations bring about within the cell, should we not expect 

 that chemical substances could be introduced, which would bring 

 about similar effects? It used to be thought that anything which hap- 

 pened to the body could not affect the germinal cells, so well 

 were they protected. However, following Muller's experiments with 

 X-rays it was found by Dr C. Auerbach and Drs Robson and Carr in 

 Edinburgh that mutations could be produced in the fruit fly by the 

 application of certain chemicals. The chemical substances which 

 they used as known as 'mustards', a reactive type of substance which 

 was developed for use in chemical warfare. It was noticed that the 

 wounds produced by 'mustard gas' were in some respects similar to 



