244 
POPULAR SCIENCE REVIEW. 
humour ; and thence the image is conducted by the optic nerve to the 
brain. The retina, too, is that portion of the eye in whose examination 
the power of the ophthalmoscope is most successfully employed. 
The instrument is a very simple one, and its action is easily understood ; 
it is in fact nothing more than a little concave metallic mirror which 
reflects a bright light into the pupil of the eye, and it has a small hole 
pierced in the centre, through which the oculist may look into the eye 
of his patient. A magnifying lens placed between the mirror and the 
patient’s eye, so as to enable the oculist to examine any symptoms of 
disease that may present themselves completes the simpler forms of the 
instrument. 
A reference to the following woodcut will assist the reader to form an 
idea of the mode in which it is 
applied. The illuminating agent is 
a jet of gas conducted from the 
wall by means of a flexible tube, 
and surrounded by a chimney of 
blue glass to moderate the light. 
The rays falling upon the polished 
mirror are reflected into the eye, 
into which the observer looks 
through the small hole in the 
mirror and also through the mag- 
nifyinglens that intervenes between 
the observer and the eye of his 
patient, and which he can adjust 
according to his wishes. 
Should the reader desire to know 
more on this interesting subject ; 
to study the optical principles 
concerned in the operation of the 
instrument, or the various forms 
which it has assumed in the hands 
of skilful opticians and oculists ; should he wish to see the “ ophthal- 
moscopic ” appearance of the interior of the ocular chamber in health or 
disease, — we must refer him to the able work before us, and he will find it 
to be one of tire first order. It is not intended (as are many such volumes) 
as a professional advertisement for the author ; but is an essay, for which a 
prize was awarded to Mr. Ilulke by the Royal College of Surgeons in 1859. 
The various forms of the instrument of which it treats are exhibited in 
well-executed woodcuts, and the exquisite chromo-lithographs by Messrs. 
Day and Son, illustrative of the appearance of the retina in health and 
disease, require no such apology as the author considers it needful to offer 
for them in his preface. 
Although an eminently practical treatise, it is, however, not exactly a 
popular one ; but we have no hesitation in cordially recommending it for 
the perusal of all medical practitioners and students, as well as to reading 
societies, public libraries, and to such readers as are in some degree 
acquainted with anatomical science. 
