500 Scientific Proceedings^ Royal Dublin Society. 



the volume of an average cell as 125 x 10"' cubic centimetres, which is the 

 volume of a cube 1/500 of an inch on the edge. 



I shall assume the surgeon inserts the radioactive needles containing the 

 emanation one centimetre apart, and that he has only one millicurie in each 

 needle, the radioactive length of the needle being one centimetre. I shall 

 also assume, as a first approximation, that the radiations are completely 

 absorbed within the boundaries of the tumour being treated. 



The number of pairs of ions generated per second by one millicurie will 

 be 2-18 X 10'". And as the needles are one centimetre apart, we have this 

 number generated per cubic centimetre. In a single cell the number is 

 272 X 10^ pairs of ions. 



In actual practice there may be about five millicuries in eacli needle. We 

 have then, theoretically, over 1'3 million pairs of ions generated per cell per 

 second. The assumption that all the rays are absorbed in the tumour is not 

 accurate, and ngain tlie numbers given apply to quite unscreened radiation 

 only. The softer /3 and -y rays suffer absorption in the glass and steel 

 envelopes. This loss applies chiefly to the rays from Ra B. In order to 

 make a safe allowance for these sources of error, as well as for the loss of 

 the most penetrating of the 7 rays of Ra C which escape from the tumour, 

 I take 50 per cent, of the calculated number of ions, that is 136,000 pairs 

 of ions per cell per millicurie per second; or, iu tlie working conditions, 

 680,000 per cell per second. In exposures measured by hours the numbers 

 rise to thousands of millions. In ten hours to twenty-four thousand millions 

 of pairs of ions per cell. 



These figures are instructive, whether they represent entirely effective 

 and useful ionisation or not. Even if only a small fraction is usefully 

 expended, they reveal the power of radio-therapeutic methods in controlling 

 or initiating chemical changes within the cell. 



The effects of this powerful ionisation on the cells of the body have been 

 demonstrated repeatedly by microscopic examination. I would refer more 

 especially to the fine series of photographs obtained by A. Clifford Morson 

 on carcinoma and sarcoma before and after exposure to radiation.' After 

 treatment for twenty-four hours with 90 mgrms. of radium the obliteration of 

 structure is far advanced or even, to all appearance, complete. In the case of 

 healthy cells of the rat, Lazarus-Barlow has shown that considerable exposures 

 may produce no more than temporary disturbanceof growth, and that even while 

 treatment is proceeding the cells may become again apparently normal.- The 



1 Morson: " Archives of the Middlesex Hospital," xxxiii, p. 110. 

 - Lazarus-Barloy, loc. cit., p. 34, 



