244 LABORATORY GUIDE JN PHYSIOLOGY. ' 



meter-angles of convergence which the individual can 

 call into play. It is the difference between the punctum 

 proximum of convergence [p c ] and the punctum re- 

 motum of convergence [r c ] expressed in meter angles; 

 which are really the reciprocals of the distances. This 

 may be thus expressed: 



CO r c = Fc ifc in distance s, or; 

 (2) a c =;p c r c in meter angles. 



Experiments and Observations. Let each member of the 

 class be in turn the subject of examination. 



(1) Determine the pupillary distance, i. e., the distance 

 from the center of one pupil to the center of the other 

 when the eyes are fixed on a distant object. One-half 

 of this is approximately equal to b, and in the experi- 

 ments which follow may be used as such. 



(2) Take a board 1 m. in length and 10 cm. in width. 

 Along the middle of one side draw a line which may 

 represent the median line; graduate the line in 

 decimeters; the proximal ^ m. may be graduated in 

 centimeters. At each centimeter or decimeter bore a 

 small hole into which a post may be set. Make two 

 posts about 5 cm. or 10 cm, in height; into the top of 

 one set a needle, split the top of the other so that it 

 will hold a card printed with fine type (not to exceed 

 1 mm. in height, finer if possible). Support the 

 board so that it shall be in a horizontal plane and 

 5 cm. or 10 cm. below the eyes. 



(3) To determine the punctum proximum of convergence-. 

 (#) Let the subject sit so that the line on the board 

 shall be in the median plane and parallel to the 

 median line; let him look at the needle when the post 

 is set at 1 m. Supposing that his punctum remotum 

 is at infinity, what is the ang. c.? 



