Page:Radio-activity.djvu/239

 with the radium emanation. The effect of an exposure under such conditions for several days or weeks has been found generally harmful and in many cases fatal. The literature in this new department of study is already large and is increasing rapidly.

Another interesting action of the radium rays has been observed by Giesel. On bringing up a radium preparation to the closed eye, in a dark room, a sensation of diffuse light is observed. This effect has been examined by Himstedt and Nagel who have shown that it is due to a fluorescence produced by the rays in the eye itself. The blind are able to perceive this luminosity if the retina is intact, but not if the retina is diseased. Hardy and Anderson have examined this effect in some detail. The sensation of light is produced both by the β and γ rays. The eyelid practically absorbs all the β rays, so that the luminosity observed with a closed eye is due to the γ rays alone. The lens and retina of the eye are strongly phosphorescent under the action of the β and γ rays. Hardy and Anderson consider that the luminosity observed in a dark room with the open eye (the phosphorescent light of the radium itself being stopped by black paper) is to a large extent due to the phosphorescence set up in the eyeball. The γ rays, for the most part, produce the sensation of light when they strike the retina.

Tommasina stated that the air exhaled by man contained a larger proportion of ions than ordinary air, and, in consequence, caused an increased rate of discharge of an electroscope. The experiment was repeated by Elster and Geitel but with negative results. On the other hand, they found that the breath of Dr Giesel, of Braunschweig, who had been engaged continuously in the chemical separation of the radio-active bodies, caused a rapid loss of charge of an electroscope. This increased rate of discharge was probably mainly due to the radium emanation, with which his system had become impregnated by inhaling the emanation-laden air of the laboratory.