816 



PHYSIOLOGY. 



perimeter, the field of indirect vision. The instrument devised for 

 this purpose is called the perimeter. 



With the perimeter the eye is made to view a fixed point from. 



which a quadrant proceeds so that the eye lies in the center of it. 



Around the fixed point the quadrant rotates, and this circumscribes 



1 the surface of a hemisphere in the center of which the eye is located. 



From this fixed point objects are slid on semicircular arms and are 



Blue 



Yellow ** 



Red 



Green 



Fig. 369. Diagram of the Normal Visual Field for White and Colors. 



(JENNINGS.) 



The outer continuous line indicates the limit of the field for white, and 

 the broken lines indicate the limits of the color fields. 



gradually placed more toward the periphery of the field of vision 

 until the object is no longer noticed. Then by moving the semi- 

 circular arm in different meridians of the field of vision we obtain 

 what is called the field of vision. The field of vision is more 

 extended below and to the outer side. It is narrowed above by the 

 brow; below by the cheek and the nose. 





