366 



PRACTICAL PHYSIOLOGY. 



[LXXV. 



scope. Kemove the eye-piece long one from an ordinary micro- 

 scope. Screw out the lower lens of the eye-piece, fix in the painted 

 disc, and block up the lower aperture with a piece of cork. Fix 

 the eye-piece in a suitable holder, and use it instead of an eye to be 

 examined. 



6. Demonstrating Ophthalmoscope (Priestley Smith}. 



The general arrangement of this instrument is shown in fig. 286. At one 

 end of the horizontal bar is a chin support for the patient ; at the other a 

 perforated glass mirror, capable of steady adjustment to any position. The 

 transverse arm near to the mirror carries a candle, provided with a light metal 

 screen on either side of it ; one of these hides the candle from the patient, the 

 other hides it from the observer, and enables him at any moment to cut off 

 the light from the mirror, and thus to protect the patient's eye from unneces- 



Fia. 286. Demonstrating Ophthalmoscope. Made by Pickard and Curry. Cost, 3, 10s. 



sary illumination without disturbing the adjustment of the instrument. A 

 wire placed in the pillar of the mirror, and movable to either side, carries a 

 piece of white paper, which serves as a fixation point for the patient's eye. 

 At the middle point of the horizontal bar is a jointed support carrying a light 

 rod, one end of which is held in the hand of the observer, while the other holds 

 the lens. By means of this rod the observer can place the lens in any desired 

 position in relation to the patient's eye. 



(l.) Arrange the instrument as in fig. 286. 



(2.) Adjust the patient's seat so as to bring his chin comfortably on the 

 support ; let him rest his arms upon the table. 



(3.) Place the rod quite horizontal, and then raise or lower the central 

 support until the centre of the lens is on a level with the patient's pupil. 



(4.) Push the lens to one side and adjust the mirror so as to throw the light 



