264 



PRACTICAL PHYSIOLOGY 



his position covers one eye and fixes the eye that is to be examined on 

 the mark at /. The quadrant is then placed, say in the vertical 

 meridian, and at the back of the wheel which revolves with the 

 quadrant is inserted in the frame a special chart adapted for recording 



FIG. 219. The perimeter. 



perimetric observations. Starting at the extreme distance the mark Ob 

 is gradually moved along the quadrant and at a certain angle the white 

 spot will be just visible. The angle indicates the limit of vision in 

 this meridian and can be recorded on the chart. Similar observations 



