6o PREVIOUS INVESTIGATIONS UPON PLANTS 



In November, 1903, Dixon ^^ reported that the growth of cress 

 seedlings was retarded by the rays from 5 mg. of '*pure" radium 

 bromide in a sealed glass tube supported at a distance of i cm. over 

 seeds sown uniformly on moist sand in the dark. The retardation 

 was apparent only in those plants situated within a radius of about 

 2 cm. from the tube, and on these seedlings the root-hairs were fewer 

 and shorter than on the others. No curvatures were evoked by the 

 rays, and when the tube was placed in a vessel of water containing 

 Volvox globator in the dark, the Volvox showed no signs of attrac- 

 tion or repulsion, or other response. Later in the same year Dixon 

 and Wigham ^^ announced that ,5 rays from radium bromide exercise 

 an inhibitory action upon the growth of Bacillus pyocyaneus^ B. 

 typhosus, B. prodigiosus, and B. anthracis in agar cultures. An 

 exposure for four days at a distance of 4.5 mm. to rays from 5 mg. 

 of radium bromide did not kill all of the bacilli, for a tube of broth, 

 inoculated from a patch thus exposed, developed organisms. 



Hoffmann'^'' found Staphylococcus pyogenes aureus, and milk 

 bacteria more resistant than B. prodigiosus. The latter on an agar 

 plate was killed by an exposure of three hours to rays from 5 mg. 

 of the bromide, passing through a mica plate at a distance of 3.5 

 mm. Pfeiffer and Friedberger^' also found the spores more resistant 

 than the bacteria of typhus and cholera, the latter being killed by an 

 exposure of 48 hours to rays from radium bromide. 



On the contrary. Van Beuren and Zinsser"^ obtained negative 

 results in every experiment with B. typhosus, B. pyocyancus, and 

 Staphylococcus pyogenes aureus. They employed 12 mg. of radium 

 of 300,000 activity, with exposures varying from 8-14 hours, and at 

 distances of from i cm. to 0.5 cm. Negative results also followed 

 the exposure of the fore arm for one and a half hours with one thick- 

 ness of a linen handkerchief intervening. 



Abbe*^ stated that the germination and growth of rape were 

 retarded in proportion to the duration of the exposure to rays from 

 *' a grain or two of radium salt," of activity not given. The seeds 

 were exposed before planting in soil, and exposure of the same kind 

 of seeds to X rays was followed by similar results. Later in the 

 same year (1904) Abbe ^ reported that the power of seed-germination 

 was weakened and finally inhibited by exposure of from two to ten 

 days, but he does not mention the kind of seed nor the amount nor 

 . tivity of the radium salt used. 



