38 A NEW OPHTHALMOSCOPE. 



the eye of a cat, I found it necessary to put it under the influence 

 of chloroform, but the image of the optic nerve, vessels, &c., upon 

 the ground glass is so very bright and clear that I do not doubt if 

 the most sensitive process be adopted, the impression could be taken 

 [instantaneously, thus rendering anesthesia unnecessary. 



POSITION. 



In either case the eye is brought to the proper position, and the 

 eye-lids held apart by an assistant. If it is the eye of a patient to 

 be photographed the instrument is mounted upon its ease, 8 inches 

 high, which, for most persons, gives it the right height. The patient 

 being seated upon a chair, as close as possible to the table, leans 

 forward towards the camera, and brings his eye as near as possible to 

 the aperture in the diaphragm, the brow rests lightly against the 

 end of the tube, and by bringing the elbow upon the table he, with 

 the palms of his hands, extemporizes a very good rest for his chin. 



The pupil of the eye to be photographed must be previously dila- 

 ted with atropine. 



PEOCESS. 



"When the instrument is in its proper position, and the light from 

 the plate glass enters the dilated pupil, the fundus of the eye is bril- 

 liantly illuminated, and its reflection passes out of the eye and 

 through the plate glass and lenses, and forms an inverted image upon 

 the ground glass at the back of the camera, where the observer in the 

 rear can see the optic nerve entrance, distribution of the arteries and 

 veins, &c., beautifully depicted, but magnified about 4 diameters. 

 If the details of the image are not perfectly defined the camera tube 

 is moved backward and forward until the proper focus is obtained. 

 This image can be seen by the observer again very much magnified 

 by placing to his eye a lens of say 6 inch focal length, and bringing 

 his eye with the lens to within 6 inches of the ground glass, but the 

 image will be seen even better by moving the ground glass to one 

 aide — the observer will then see the aerial image of the reflection 

 from the eye which will occupy the same position as the ground 

 glass previously occupied, (see Definition 8). In photographing, the 

 slide containing the ground glass is removed and a slide substituted 

 containing a plate glass " prepared " by the ordinary collodion pro- 

 cess. An " exposure " of about 5 seconds is sufficient. If the 



