1904-5.] Action of Radium Bromide on Eyeball of Frog. 835 
On the Action of Radium Bromide on the Electromotive 
Phenomena of the Eyeball of the Frog. By John G. 
M‘Kendrick, M.D., F.R.S., and Walter Colquhoun, 
M.A., M.B. 
(MS. received June 3, 1905. Read July 3, 1905.) 
It has been known for the last thirty-four years that when the 
fresh excised eyeball of a frog is connected by non-polarizable 
electrodes with a sensitive galvanometer, an electrical current 
(travelling through the eye from the retina to the cornea) may be 
detected, and that variations occur in this current, due solely to 
the action of light on the retina.* 
It is also well known that salts of radium are luminous in the 
dark, and that if a tube containing radium f is pressed against the 
closed lid of the eyeball, or even pressed against the temple, one has 
the consciousness of luminosity. This being so, it was of interest 
to ascertain whether this luminosity was due to the radium causing 
fluorescence of any of the structures of the eyeball, or whether it 
was due to the direct action of one or other of the emanations of 
radium on the retina itself. 
Dr Hardy of Cambridge kindly lent us a specimen of radium 
bromide enclosed in a small leaden capsule and covered on one 
side with mica. This was used in the experiments to be described. 
The mica cover prevents the escape from the radium of the 
a particles, so that any effect observed was due to the action of 
the /3 or y rays, or of both conjointly. 
* This phenomenon was first observed by Holmgren, of Upsala, in 1871 : 
it was investigated independently by Dewar and M ‘Kendrick in 1872-3 ; and 
since then it has been examined by Kiihne and Steiner in 1880-1, by 
Engelmann and Grijns in 1891, by Fuchs in 1894, by Beck in 1899, and by 
A. D. Waller in 1900. The bibliography is fully given by Waller at the end 
of his paper, “ On the Retinal Currents of the Frog’s Eye, excited by light 
and excited electrically,” in the Phil. Trans. Roy. Society, vol. cxciii., B. 
1900, p. 163. The time relations of the phenomenon have also been elabo- 
rately investigated by Gotch, Jl. of Physiology, vol. xxix. p. 388, 1903, and 
vol. xxxi. p. 1, 1904. In the last paper he specially studies the effects of 
monochromatic light. 
t By “ radium ” is always meant “a salt of radium.” 
