No. 504] PHYSIOLOGICAL EFFECTS OF RADIUM RAYS 763 



and lower velocity, are less penetrating than the B par- 

 ticles, but are much more effective ionizers. The y rays 

 behave as X rays. 



In addition to the three types of rays above described, 

 radioactive substances are the source of a heavy, inert 

 gas, belonging to the argon family. This gas, named by 

 Rutherford the emanation, 3 is itself radioactive, giving 

 off only a. rays. 



Studies of the physiological effects of radium, there- 

 fore, must take into consideration the three types of rays, 

 described above, and also the radioactive gas, the emana- 

 tion. In the experiments recorded below, the radium, in 

 the form of radium bromide, was contained in sealed 

 glass tubes, or employed as a thin coating on a suitable 

 surface. In the former case only X and y rays were 

 available, as the a rays and the emanation can not pass 

 through the walls of the tubes. In the latter case the a 

 rays together with the emanation were also available. 



The effects of radium upon plants have been investi- 

 gated by Dixon and Wigham 4 in Great Britain, by Koer- 

 nicke 5 in Germany, by Guilleminot in France, and by 

 several others. Without going into the details of their 

 work it may be stated that the general conclusion from 

 their experiments is that the rays exert either a retard- 

 ing or an inhibiting effect on physiological processes. 

 Koernicke, however, found some evidence that accelera- 

 tion of activity might follow exposure to the rays under 

 suitable conditions. 



My own investigations have led to the conviction, al- 

 ready reported, 7 that radium rays act as a stimulus to 



8 The use of the plural 1 1 emanations ' ' to designate all the rays and 

 influences coming from radium, has been somewhat common in biological 

 papers. It has no warrant, is only confusing, and should be abandoned. 



'Nature, 69: 81. 1903. Proc. Boy. Dublin Soc. Sci., N. S., 10^: 178. 

 1904. Notes Bot. School, Trinity Coll., Dublin. 1: 225. 1905. 



s Ber. Deut. Bot. Ges., 22: 148, 155. 1904; 23: 324, 404. 1905. 



6 Compt. Bend. Acad. Sci. Paris, 145: 711. 1907; Compt. Bend. Assoc. 

 Frangaise Adv. Sci,, 36* : 389. 1907; 36*: 1344. 1908; Compt. Bend. Acad. 

 Sci. Paris, 145: 798. 1907. 



'"Effects of the Rays of Eadium on Plants." New York, 1908. 

 {Mem. N. Y. Bot. Garden, Vol. IV.) 



