1904-5.] Action of Radium Bromide on Eyeball of Frog. 837 
lead was used as a screen, which could be placed between the radium 
and the eye at pleasure. We have found this little dark chamber 
of great service in these experiments. 
Recognising the fact that the luminosity of radium, or of bodies 
rendered fluorescent by radium, is most apparent after the eye 
has been kept for some time in the dark, we made use of the 
eyeballs of frogs that had been kept for at least forty-eight hours 
in absolute darkness, and the animal was killed and the eyeball 
was usually dissected out in monochromatic red light, such as is 
used in a photographic chamber. We found that this procedure 
greatly increased the sensitiveness of the eye to light, when the 
experiments were made in the usual way with a lighted match or 
taper, or when the shutter in the upper surface of the box was 
opened so as to allow the light from a few incandescent lamps to 
fall on the eyeball from an electrolier hung about 12 feet above 
the apparatus. 
In the dark box a small brass forceps was arranged so as to hold 
the leaden capsule containing the radium in such a position that 
the radium was directed to the cornea of the eyeball placed on 
the clay pads of the electrodes. As already described, the movable 
lead screen could be pushed out and in. When “ in,” the T-shaped 
piece screened off the radium from the eyeball : when “ out,” 
the radium acted on the eyeball. “ Radium on ” was obtained by 
pulling the lead out ; “radium off,” by pushing it in. 
Expt. 1. Eye placed on the mica cover of the capsule and the clay points 
brought into contact with fundus and centre of cornea. Resting current, 60 
divisions on scale. Current steadily fell in five minutes from 60 to 28. 
Steady for five minutes at 24 divs. ; then “light on,” rise to 27, fall to 
26, rise to 29 divs. ; “light off,” rise to 30, then fall to 21 divs. 
Expt. 2. (a) Eye readjusted on electrodes with radium capsule screened off 
by lead plate. Resting current, 25 divs., fall in two minutes to 22 divs. 
Radium on, rise to 24 divs., remained steady for one minute; radium off, 
rise to 26 divs., fall to 21 divs. 
(&) Resting current, 18 divs. Radium on, rise to 19 '5 divs., fall to 19, 
rise to 20 divs. ; radium off, rise to 21 divs., fall to 17 divs. 
These experiments are typical of others. It would appear that 
radium rapidly diminished the initial resting current, but the per- 
centage of increase produced both by radium “on” and radium “off” 
was sometimes greater than with ordinary light “on” and “off.” 
