164 
PROCEEDINaS OF SOCIETIES. 
cabinet, and stated tliat a fragment of the same, placed in tlie hands 
of a London microscopist by Captain Mortimer, corresponding 
member, had proved exceedingly interesting, and to contain some rare 
minnte forms of fossil DiatomaccEe. 
The feature of the evening was a lecture by Dr. Adolp Barkan 
" On the Construction and Uses of the Ophthalmoscope." The Doctor 
used the black-board with facility, giving a technical description of the 
various parts of the human eye, aided by frequent diagrams, and 
illustrated by reference to the eyes of a rabbit and a hog, from which 
the light of other days had departed. 
Commenting on the need of an instrument to enable one to see the 
interior of a living human eye, he stated that up to 1845 no such had 
been obtained ; but acting on the fact then discovered, that light 
entering the eye was not absorbed but reflected, and that the interior 
of the body could be made luminous. Professor Helmholtz, in 1851, 
invented an instrument which had the desired effect of illuminating 
the eye; and catching the rays in tbe rebound, so to speak, the 
observer found a new field for his scientific powers. 
The practical uses of the ophthalmoscope are of enormous value, 
as the diagnosis of a disease in and on the rear portion of the eye can 
be made without guesswork, the various substances and coats of the 
optic being shown with astonishing clearness. 
After exhibiting patterns of the instrument, and stating that 
although some forty odd varieties had been invented, none were of 
any practical improvement on the one first produced by Helmholtz, 
who had seemed to hit on the right thing at once, Dr. Barkan brought 
out his menagerie of living animals and proceeded to demonstrate 
what could be seen. 
An immense frog, strapped to a piece of board, stared and blinked 
at the interested scientists, and proved himself a tractable and worthy 
aid to the evening's study. A subcutaneous injection of a solution of 
cinnabar filled his blood-vessels with minute crystals, and pouring 
down the interior of the eye could be seen the coursing blood, with 
now and then a flashing sparkle of the ciimabar. 
A rabbit claimed its share of attention, and the instrument 
brought out the peculiar construction of its eye, the absence of 
pigment and insertion of the optic nerve being noticeable. 
A cat, swathed and enclosed in a heavy sack for obvious reasons, 
attracted her quota of observers, and richly repaid them all. The 
peculiar manner in which the light was reflected in colours of red, 
green, and yellow, made a picture not before deemed possible to the 
casual observer. 
A pleasantly disposed dog was interviewed with the instrument, 
and quietly permitted an intelligent gleam to sparkle forth, showing 
much the same beauties as were by his feline friend and co-labourer 
in the good cause. 
After voting the Doctor a hearty vote of thanks for his delightful 
and interesting lecture, the meeting adjourned. — Cincinnati Medical 
News. 
