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EXPERIMENTAL PHYSIOLOGY. 



LESSON LXII. 



PERIMETRY IRRADIATION IMPERFECT 

 VISUAL JUDGMENTS. 



1. To Map out the Field of Vision, or Perimetry. 



(a.) A rough method is to place the person with his back 

 to a window, ask him to close one eye, stand in front of him 

 about two feet distant, hold up the forefingers of both hands 

 in front of and in the plane of your own face. Ask the 

 person to look steadily at your nose, and as he does so, 



Fig. 129. Priestley Smith's Perimeter. 



observe to what extent the fingers can be separated hori- 

 zontally, vertically, and in oblique directions before they 

 disappear from his field of vision. 



