1904-5.] Action of Radium Bromide on Byeball of Frog. 841 
J3 rays by means of glass. A little frame was made into which 
was fitted by superposition thirteen microscopic cover -glasses, 
giving a total thickness of 4 mm. This frame could be interposed 
between the radium and the eye by the same method as that 
followed with the lead plate. 
Expt. 9. Eye placed on pads. Resting current, 60 divs. Radium on, rise 
of 1 div., slight fall, rise of 5 divs. ; radium off (by interposition of glass), 
just a perceptible rise, then a fall to original position. After three minutes, 
experiment was repeated. Radium on, rise of 2 divs., fall of 5 divs., then a 
rise of 5 divs. Radium off (glass interposed), barely perceptible rise, then fall 
to original position. 
This was not a conclusive experiment. Several other experi- 
ments were performed, which generally showed that the effect of 
radium was less when the glass slips were interposed, but we are 
not quite confident on this point. 
Our general conclusions are : — 
(1) That the light emanating from radium bromide affects the 
electromotive phenomena of the living retina of the frog in a 
manner similar to that of ordinary light, although to a considerably 
less degree. 
(2) That this action is not due to fluorescence of any of the 
structures of the eyeball, but to direct action on the retina. 
(3) That the retina of the frog’s eye will still respond to 
emanations of radium passing through cardboard, blackened 
paper, thin glass, and aluminium foil, emanations which, when 
allowed to fall on the human eye in a perfectly dark chamber, do 
not give rise to a luminous sensation. 
(4) That the frog’s retina is susceptible to the feeble light 
emitted from the surfaces of fluorescible minerals and fluids 
rendered fluorescent by radium. 
(5) That the /3 rays are responsible for most of the effects 
observed, but that after those have been largely excluded, a slight 
effect still persists which, presumably, must be due to the y rays. 
(6) That monochromatic light which is employed in a photo- 
graphic chamber may still alter the electromotive phenomena of 
the living retina of the frog. 
Note . — We note that Kiihne and Steiner, and also Gotch, found 
the advantage of using the eyes of frogs that had. been kept for 
