62 PREVIOUS INVESTIGATIONS UPON PLANTS 



ions through neutralization of the H ions by the electrons from the 

 radium. It is recognized that the coloration may be due to direct 

 ionization of the phenolphthaline as well as of the water. Further 

 experimentation, however, showed that the detection of electrons by 

 means of this indicator is very uncertain. The same agar prepara- 

 tion became pink when supported over a solution of caustic potash * in 

 a closed chamber. 



In a note on the action of radium on microorganisms, A. B. 

 Green ^* states that the specific germ of vaccine is killed after 22 hrs. 

 exposure to radium rays from i eg. of <' practically pure radium 

 bromide," contained in a vulcanite and brass capsule, fronted with 

 thin talc. Only the [-i and y rays were thus available. Staphylo- 

 coccus pyogenes aureus, S. pyogenes albus, S. cereus jlavus, and S. 

 cereus albus were less resistant than the specific vaccine organism, 

 and spore-forming bacteria were most resistant, requiring 72 hrs. to 

 kill. It is further stated that, after an exposure of from 24-120 hrs., 

 the microorganisms themselves ma}'^ exhibit radioactivity. It is con- 

 sidered uncertain as to whether or not living organisms can acquire 

 this power, but those killed by the rays can do so. It is impossible 

 to conceive how the organisms, dead or alive, could become radio- 

 active as a result of their exposure to a radium salt in a sealed con- 

 tainer. If the container was not perfectly sealed, however, then 

 traces of the emanation might diffuse out and thus cause induced 

 activity of the organisms. 



Willcock ''^ stated that an attempt by Mr. Hardy to secure photo- 

 synthesis in liverworts by the energy of radium rays was unsuccess- 

 ful, and that Dr. Anderson had shown that the tissues of leaves may 

 be killed by the rays. 



Koernicke's ^^ paper on the influence of radium rays on germina- 

 tion and growth appeared twelve days after that of Dixon and Wig- 

 ham. He found that the growth of the roots of Vicia Faha in 

 sawdust was inhibited when a sealed glass tube of radium bromide 

 was placed close by the elongating tip. The radium was removed 

 at the end of four days, but growth was not resumed, though the 

 roots remained alive for over a month after they had ceased to grow. 

 When dry seeds of Vicia Faha were exposed for 24 hrs. the subse- 

 quent growth of the root was retarded, but the shoot did not appear 



\' * The radioactivity of potassium, discovered by Campbell (p.'sz), was not known 

 at the time of publication of Dixon and Wigham's experiments. 



