158 MR JAMES DEWAR AND DR M‘KENDRICK ON THE 
05. Introducing these values in equation (4), we can find what is the ratio of 
the sensational intensities for any assigned values of the luminous intensity. 
In this way, if the amount of light varies as 100: 1, then the corresponding sen- 
sational values may differ as 3:1, or 5:1. Contrasting the above values with 
the electrical variations previously given for the same difference of luminous in- 
tensity, we observe a close agreement that can scarcely be regarded as accidental. 
It would thus appear that the psychophysical law of FecHNER is not dependent 
alone on perception in the brain, but in part on the structure of the eye itself. 
The effects which occur on, during, and after the action of light on the retina 
also take place after the eye has been removed from all connection with the 
brain. Thus the law of FECHNER is not a function of the brain alone, but is 
really a conjoined function of the brain and the terminal organ, the retina. 
VII.—EXPERIMENT ON THE EFFECT OF MOONLIGHT. 
Although in previous experiments we endeavoured to eliminate the effects 
of heat from those of light, we thought it advisable to note the effect of moon- 
light, which is well known to contain heat rays so few in number as to require 
the most sensitive arrangement for their detection. The experiment was 
accordingly made on a clear moonlight night. The troughs, with the eye 
placed on the cushions, were carried into the open air, and were connected by 
long wires with the galvanometer. It is sufficient to state that in these circum- 
stances we found the eye as sensitive to moonlight as to the light of a candle 
placed at a distance of five or six feet. 
VIII.~Errects oF CERTAIN ACTIVE SUBSTANCES ON THE SENSIBILITY OF THE RETINA. 
The subcutaneous injection into the frog of lethal doses of woorara, santonin, 
belladonna, morphia, and Calabar bean, does not destroy the sensibility of the 
retina to light. The change in the electro-motive force was not altered quanti- 
tatively to such an extent as to be appreciable. This is most remarkable in the 
case of santonin, which is well known to produce in man sensations of yellow 
light. 
TX.— EXAMINATION OF OTHER TEXTURES OF THE HYE. 
It is manifest that in an investigation such as this, it is of great importance 
to examine the action of light on the various textures or tissues composing the 
globe of the eye and the adjacent skin, so as to determine whether or not these 
are affected by light. 
1. The Skin.—As has already been shown by Du Bois-REymonp and many 
others, there is no difficulty in obtaining a strong deflection when the clay points 
are applied to the skin of the frog, one to the inner and the other to the outer 
surface. From the well-known experiments of LisTER on the pigment cells in — 
the skin of the frog, in which he showed that the pigment molecules changed 

