II. OPHTHALMOLOGICAL. 787 



A more detailed description will be found in Zchender's Klinischen Monat- 

 schriften fur Augenheilkunde, 1869, p. 411. 



3681. Cohn's Refracting Ophthalmoscope. 



Prof. Dr. H. Cohn, Breslau. 



In the year 1871 the exhibitor constructed this apparatus for examining as 

 quickly as possible a number of scholar's eyes. In 1872 the instrument was 

 described in the Klinischen Monatsbl. of Augenheilkunde, in the October 

 number. Twenty-four glasses can be quickly pushed past behind one and 

 the same mirror. As the disc which bears these glasses is centred above 

 the mirror, the nose of the observer cannot come into contact with it. 

 There is no necessity to shift three discs with glasses, as in Loring's Ophthal- 

 moscope. If the mirror be placed in front of the eye to be examined, and the 

 patient looks through the central hole at some letters in the distance placed 

 on an inclined table desk (as Snellen's alphabet), the instrument can be used 

 instead of a test lens, and thus the wearisome selection of the glasses is 

 avoided ; in the same way, by quickly turning the disc with the correction 

 glasses, its refrangibility for an object can be removed. 



3682. Cohn's Exophthalmometer, three specimens. 



Prof. Dr. H. Cohn, Breslau. 



These instruments possess a certain amount of interest, as they are almost 

 the first instruments which were made for measuring the prominence of the 

 eye from the orbit. Dr, Cohn exhibited the first of the accompanying instru- 

 ments, on Nov. 17th, 1865, before the Medical Society of Breslau, and at the 

 same time gave it the name of Ophthalmoprostatometer ; but later, in the 

 year 1867, he changed the name to Exophthalmometer. The second in- 

 strument which accompanies the first Dr. Cohn has not publicly demonstra- 

 ted, as he altered the principle of measurement ; nevertheless he determined 

 to send the instrument, so that one can judge of the reasons which induced 

 him to regard the external wall of the orbit which he had taken as his fixed 

 point (and is still so taken by some) as not suitable for the purpose. The 

 third exophthalmometer with which the exhibitor finally carried out his 

 measurements, was laid before the Ophthalmic Congress, at Paris, on the 12th 

 of August 1867. Its peculiarities and applicabilities are described in the 

 accompanying pamphlet. 



3683. Several Fairs of Cohn's Mica Spectacles, manu- 

 factured by M. Raphael in Breslau. 



Prof, Dr. H. Cohn, Breslau. 



In February 1868 the exhibitor examined the eyes of 1,283 metal workers 

 and, in consequence of the enormous frequency of injuries to them, caused the 

 first pair of mica spectacles to be made. They cannot splinter, and are 

 extremely cheap. They are recommended for workmen who manipulate 

 explosive materials. In the accompanying pamphlets is shown the gradual 

 perfection to which these glasses have been brought by the manufacturers, 

 Messrs. Max Raphael, in Breslau, under Dr. Cohn's directions. 



3684. Apparatus for giving Instruction in the use of 

 the Ophthalmoscope; also 18 water-colour drawings in a box, 

 giving the typical aspects of the retina in health and disease, 

 from nature. Dr. Magnus, Breslau. 



This apparatus presents, in a very instructive way, the various laws of refrac- 

 tion of the eye, by shifting the lens which is contained in it ; the apparatus 



3D 2 



