1903.] Oxidising Action of the Bays from Radium. 203 



Professor Rutherford was good enough roughly to measure the 

 stopping power of the screens actually used. Nos. 2, 3, 4, and 5 

 stopped all the a rays. No. 6 stopped 80 per cent, of the ft rays, and 

 allowed the 7 rays to pass. No. 7 stopped practically all the ft rays, 

 and allowed only 7 rays to pass. 



The obvious conclusion from these figures is that the action is mainly 

 due to the /3 rays that is to say, to the stream of negative electrons. 

 On the other hand, the fact that action is not arrested by as many as 

 four of the lead screens makes it certain that the very penetrating 

 7 rays also are chemically active. 



As the 7 rays are said to be the same as the Rontgen rays that is 

 to say, ethereal pulses the action of the latter was tried by exposing 

 tubes of iodoform dissolved in chloroform, which were enclosed in 

 light-tight cardboard boxes. The Rontgen rays were found to be 

 active, the solutions were purple at the end of 15 minutes. 



An exact comparison of the relative activity of light, radium rays 

 and Rontgen rays cannot be attempted, but the experiments prove 

 that light is the most active. The difference appears to be very great. 

 The profound and often lethal physiological action of radium rays must 

 therefore, for the present, be looked upon as being due to their power 

 of penetration rather than to the fact that they exert any novel or very 

 intense action. They reach parts which are shielded by a cuticle very 

 impervious to light waves. Viewed in this way the pigmentation of 

 the human skin found in tropical races, and in those exposed to 

 sunlight, may be regarded as an increased protection to the internal 

 structures which acts by increasing the opacity of the epidermis. 



One of us has already shown that the a rays profoundly modify the- 

 physical state of colloidal solutions.* If the colloid particles be 

 electrically negative, the a rays act as coagulants ; if the colloid 

 particles be electrically positive they act as solvents, that is to say, the 

 rays decrease the average size of the particles. 



As a provisional basis for investigating the physiological action of 

 radium rays we may therefore regard the a rays as altering the physical 

 state of the living matter, the ft and 7 rays as altering the chemical 

 processes, especially perhaps the oxidation processes of the tissues. 



It may be well to mention briefly the instances of chemical decom- 

 position produced by radium rays which have been described up to 

 the present. 



Berthelotf gives the following cases. lodic acid is decomposed 

 with liberation of iodine by rays from radium and by light. Unlike 

 the liberation of iodine from iodoform the change proceeds very slowly,, 

 free iodine being present only after 14 days' exposure. Nitric acid 



* ' Journal of Physiology,' vol. 29, 1903, p. xxix. 

 f ' Comptes Hendus,' vol. 133, 1901, p. 659. 



