498 Scientific Proceedings, Royal Dublin Society. 



They may kill such cells. They may also in very feeble doses promote cell 

 division. Graskell has specially studied the efEects of X rays on the embryonic 

 cells of the chick. ^ He found tliat up to a certain amount of exposure the 

 embryo may make complete recovery from the injurious effects of the rays, 

 but that there is a critical dosage be3'ond which recovery does not occur and 

 development stops. Certain ultra-violet rays — the Schumann rays — are said 

 to be always very destructive in their action on living protoplasm, giving 

 rise to cytolysis and death in the cases of spirogyro, amoeba, and other 

 unicellular organisms, in less than one minute. These wave-lengths, which 

 are about half the length of visible rays in the violet, are rapidly absorbed 

 even in air. It has been suggested that destructive organic effects are due to 

 untimely oxidation. 



The physician possesses in radiation a subtle means of attacking tlie 

 mechanism of cell-growth, and one of unlimited power. It is a characteristic 

 feature of true scientific advance that new powers, based on newly discovered 

 forces, are placed at our disposal. The conception of physical interference 

 with the atomic linkages of organic structure and its sustaining metabolic 

 processes, is a new one. The older practice recognized one way only of 

 affecting such interference — by the intervention of chemical actions set up 

 by drugs assimilated through the digestive system. Altliough we are to-day 

 far from a knowledge giving complete control of radiative efEects, I venture 

 to think that these will ultimately be found to be more definable and 

 manageable than medicinal treatment. 



Let us consider, so far as we can, what we are doing when we insert into 

 a tumour a needle filled with emanation. 



Within the tube the radioactive transformations of the atom are attended 

 by three forms of radiations. 



(1) a rays, which are positively electrified helium atoms, and which can- 

 not pass the walls of the tube. With these, therefore, we have nothing to do. 



(2) Also /3 rays, or electrons, are sent out. Some of these are so slow 

 as also to be stopped by the thin glass and steel walls surrounding the 

 radioactive substances. But these walls are thin enough, as used in the 

 technique introduced by the Hadiura Institute of the Royal Dublin Society, 

 to permit a large proportion of them to escape. Their velocity varies over 

 a wide range, some electrons moving at speeds nine-tenths that of light. 

 Their velocities are such as to give, as already stated, both a line and a 

 continuous " spectrum " when sorted out by a magnetic field. 



These electrons are known to be the direct agents in effecting ionisation. 



' Giiskell : rroc. Roy. Soc, Ser. B, vol. Ixxxiii, Feb., 1911, p. 305. 



