PREVIOUS INVESTIGATIONS UPON PLANTS 6l 



Experiments on the physiological effect of a rays were made by 

 Baeyer.*" He employed radioactive lead and " induced " silver, pal- 

 ladium, and polonium. The a rays from these preparations killed 

 bacteria, but did not affect the skin. 



Dauphin ^^' ^^ was the first to investigate the effect of radium rays 

 on the lower fungi. He found that growth was retarded in cultures 

 oi Alortierellay Mucor^ Piptocephalis, and Thamnidmm. Spores of 

 Mortierella would not germinate in the neighborhood of the radium 

 tube, but germinated as soon as the tube was removed. The growth 

 of hyphae was arrested, and outgrowths were formed on the filaments. 

 The plasma withdraws from the influence of the rays, and septation 

 of the hyphae takes place, followed by encystment. On the removal 

 of the radium, growth recommences. 



The most extensive paper, up to the date of its publication, was 

 that of Dixon and Wigham,^*^- ^^ which appeared in March, 1904. In 

 all of their experiments these authors used 5 mg. of radium bromide 

 in a sealed glass tube, but the activity (presumably 1,500,000) is not 

 given. They found that the seedlings of Lepidium sativum were 

 not radiotropic, but grew less rapidly, and had fewer and smaller 

 root-hairs when exposed to the rays. Volvox glohator (" positively 

 photoscopic ") gave no reaction to the rays. The failure of Bacillus 

 ^yocyaneus, B.^rodigiosus^ B. typhosus, and B. anthracis to develop 

 under the influence of the rays is attributed, not to the direct effect of 

 the rays on the organisms, but to a probable change in the agar. 

 The effects are thought to be due more to the /9 than to the y rays, for 

 the latter are too penetrating to be absorbed by 30 mm. of air, and 

 beyond this distance the radiations were apparently without effect. 

 It is suggested that the electrons, emitted directly by the radium, or 

 produced indirectly by it, were partly absorbed by the bacterial cul- 

 tures. They possibly attach themselves to the positive ions of the 

 cultures, among which are the hydrogen ions of the water. Thus 

 OH ions would be set free, and the water in the protoplasm would 

 become alkaline. This would check the action of the enzymes on 

 which the metabolism of the cells depends, for most enzymes, except 

 trypsin, are inhibited in an alkaline solution. In support of this 

 hypothesis it was found that colorless phenolphthaline, diffused 

 through an agar culture, acquired a feeble pink color when the 

 preparation was exposed for a day or two to the radium rays. This 

 the authors explain as being due to the liberation of negative OH 



