192 



ADVANCED LESSONS IN PRACTICAL PHYSIOLOGY 



metal arch. While the subject gazes fixedly at the mark in the center 

 of the arch, move these colors interchangingly from without inward 

 along the different meridians of the eye. As soon as the subject per- 

 ceives the color clearly, indicate this point in degrees upon the smaller 

 chart. Eventually, connect all the points of the same color with one 

 another. 



FIG. 112. PERIMETER CHART TO SHOW THE FIELD OF VISION FOR A RIGHT EYE WHEN 

 KEPT IN A FIXED POSITION. 



While the results differ materially with the saturation of the dif- 

 ferent colors, most generally the red field is the largest, then follows the 

 blue, and lastly the green. 



7. Entoptic Phenomena Produced by the Tears. Evoke a mild 

 hypersecretion of lacrimse by holding a cut onion at some distance be- 

 low the eye or imitate this condition by moistening the eyelids with 

 fresh water. Close the eyelids somewhat, so as to deepen the layer of 

 lacrimae upon the central area of the cornea. What effect has this 

 upon refraction and the formation of the retinal image? Draw a dia- 

 gram to show how refraction is affected under water. 



