LETHAL EFFECT OF RAYS 163 



kind. In general, the lower the velocity of the ray, the greater its 

 physiological action, provided always that its xclocity is sullliciently 

 great to produce any physiological effect. (A high velocity bullet 

 cuts a clean hole in a piece of glass, while a spent bullet shatters 

 the glass.) The effect seems to depend more on the xelocity of the 

 ray than on its nature, e.g. a rays have mass while the others have 

 not, yet similar actions may be produced under proper conditions. 

 The physiological effect of any ray is proportional to its power to 

 ionise air. ^ rays have 00 times the ionising power of y rays, and 

 experiment has shown that y rays require to operate for 60 mins. 

 on li\'ing matter to ha\'e the same effect as one minute's exposure 

 to /3 rays. That is, by varying the length of exposure, similar 

 results may be obtained from radiations having different ionising 

 powers. If rays are classed according to their power to ionise 

 air, then those having the greatest ionising effect have an inhibitory 

 rather than a beneficial effect on living organisms, while, con- 

 versely, the weaker rays promote the function of the organism. 

 The power of ionisation being equal, then generally a long exposure 

 produces inhibitory effects and a brief exposure beneficial. For 

 example, exposure of the fertilised eggs of arbacia to rays of radium, 

 if short, causes stimulation of the cell function. If the radium is 

 applied during the approach of the germ nuclei, then cell division 

 is accelerated. If the exposure is long, cell division is retarded. 

 The effect of radium is more marked during the metaphase than 

 during either the prophase or the telophase. Eggs are not so easily 

 influenced by radium emanations after the dividing stage is passed. 

 In order to produce any effect on the rate of growth of ascaris eggs 

 about ten times the intensity of radium has to be applied as was 

 effective during the dividing stage, or the length of exposure has to 

 be increased tenfold. The /3 and y rays seem to act on different 

 parts of the egg. The nucleus, especially if it is undergoing 

 mitosis, is influenced by the y rays, while the j8 radiation has most 

 effect on cytoplasm. The fertilisation membrane of nereis is 

 thickened as a result of exposure to radium, the length of 

 exposure being, in this case at least, more efficacious than the 

 intensity. 



The rays emitted by radio-active elements, especially radium, 

 have been employed extensively in the treatment of morbid cell 

 growths. The cells are not killed outright, but division of the 

 nuclei is inhibited, eventually leading to death of the cell. The 

 rays are capable of causing definite regressive changes even in deep 

 seated tumours such as mediastinal lympho-sarcoma, carcinoma of 

 the lungs, and abtloniinal metastases of carcinoma of the testis. 



Several investigators have reported results to show that the 



