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Published online by Cambridge University Press: 15 September 2014
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† 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.
page 835 note * 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 Kühne 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 elaborately 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.
page 835 note † By “radium” is always meant “a salt of radium.”
page 836 note * These I used because I have been accustomed to them for thirty-five years.—J. G. M'K.
page 840 note * Note by J. G. M'K. I have seen hundreds of the original experiments during the last thirty years, but I have never met with an eye so sensitive as this one.
