Vol.. 8, 1922 
ZOOLOGY: A. S. GILSON, JR. 
131 
concentration of pigment between 70 and 80. In dark animals, the 
average extension of the retinal pigment is 59, the pigment being massed 
at the outer region of the retina. 
Retinas were examined of normal light fish, of normal dark fish, and of 
light and dark fish some of which had received intramuscular, some intra- 
abdominal injections of physiological salt solution, of adrenalin 1: 1,000, 
or of adrenalin 1 : 10,000. The adrenalin used was that prepared by Parke 
Davis and Company and sold as "Adrenalin 1:1,000." The adrenalin 
was allowed to act for varying times before the retinas were fixed, with 
the results that the greatest effect was found to occur in those dark ani- 
mals which had been injected with 0.2 cc. of adrenalin 1: 1,000, and be- 
tween thirty minutes and one hour after injection. 
Of the animals to be experimented upon, those to be used as dark animals 
were kept in a photographic darkroom for at least sixteen hours before be- 
ing treated; those to be used as light animals were placed in a white dish 
which was kept for at least a day by a north or west window and the fish 
were treated and killed between one and three o'clock in the afternoon. 
The animals were killed by quick decapitation with a pair of scissors, the 
head was opened longitudinally, and immersed in Bouin's picro-formol 
mixture. Fixation was allowed to proceed for about fifteen hours. The 
eyes were then dissected free from the head, washed thoroughly in 70% 
alcohol and dehydrated in 90% and absolute alcohol. While in absolute 
alcohol, the cornea of each eye was sliced off with a razor and the lens re- 
moved with a pair of fine forceps. The eyes were then cleared in xylol, 
infiltrated and imbedded in paraflin and serial sections were cut, in most 
cases 7 micra in thickness, and in a plane perpendicular to the face of the 
eye and through the optic nerve. Measurements could thus be made on 
radial sections at a point about half way from the entrance of the nerve to 
the outer rim of the retina. For measuring, a high dry objective and cam- 
era lucida were used, projection being made upon a line ruled along a sheet 
of paper and upon which the actual measurement was made. All ex- 
periments were performed at room temperature. 
The results obtained are summarized in Table A. The values given in 
the table are the averages of all experiments for each class, plus or minus 
the probable error (P. E.) as obtained by the use of Bessel's formula. 
This probable error indicates the relative value of the results by taking 
into account not only the standard variation of each series but also the 
number of experiments performed. 
It will be seen that when light animals are injected with 0.2 cc. of ad- 
renalin 1 : 1,000, there is no significant change in the width of the pig- 
mented region of the retina. In dark animals which had been injected 
into the body cavity with 0.2 cc. of adrenalin at the strength of 1: 1,000, 
there was shown a marked change of the pigment position, the pigment 
