166 APPENDIX. 
APPENDIX. 
18th February 1874. 
While this paper was passing through the press, we have been fortunate 
enough to have obtained information from a Swedish lady that a paper relating 
to the same kind of work had appeared in a Swedish Journal. We, accordingly, 
endeavoured to obtain this paper, which we find to be one by Professor 
HoimeGren, a distinguished physiologist, published in the “Upsala Lakere- 
forenings Forhand lingar,” vol. vi. 1870-71, No. 5, p. 419. It is with pleasure 
we at once acknowledge that he has the claim of priority in observing an electrical 
fluctuation by the action of light, and that his memoir is a valuable contribution 
to science. It is, however, almost needless to state that our work was done in 
entire ignorance of any previous observations on the subject, and that our methods 
of experiment, the delicacy of our instrument, and the distinct numerical data 
obtained, have enabled us to prosecute the matter in various new directions. 
EXPLANATION OF THE PLATES. 
Puaty X. 
This Plate shows the arrangement of the apparatus. 
A. Galvanometer. 
B. Scale. 
C. Key. 
D. Du Bois-Reymonn’s non-polarizable electrodes having the eye placed between the clay points. 
E. Moist chamber, consisting of an annular glass vessel of at least two inches section, filled with 
water, and placed over the electrodes to keep the temperature uniform, and absorb radiant heat. Over 
this is placed a blackened box, the outlines of which are marked in dotted lines, having a moveable 
shutter in front, F. 
G. Lamp. 
Puate XI. 
This plate shows curves representing variations in the electro-motive force of the eye produced by 
the action of light; or they represent the path pursued at different times by the image reflected from 
the galvanometer mirror if the plate were supposed to move vertically upwards. The dotted lines repre- 
sent the normal position of the galvanometer-image in the dark; and the complete dark lines represent 
the position of the image during and subsequent to the action of light. 
I. and If. Actual curves taken from the living eye of the cat on a cylinder moving horizontally. 
IIL, IV., and VI. Graphical curves representing the general action taken by time observations. 
III. and VI. Frog. IV. Toad. V., VIL, VIII., and IX. Actual curves taken on a cylinder from the 
eye of a frog. 
X. and XI. Curves obtained from eye of cat removed as quickly as possible from dead body. 
The four dotted horizontal lines divide the time of the experiment into four equal intervals, 
namely, Ist, in darkness; 2d, during action of light; 3d, during continued light; and, finally, on 
removal of light. A movement to the right of the dotted line indicates an increase, and to the left a 
diminution, in the electro-motive force. 

