XLVIII. Accommodation and convergence. 



In the above experiment with the excised rabbit's eye 

 one notices a marked blurring of the image when the eye 

 is brought near the object. Though the definition of the 

 image is sharp at 5-6 meters or beyond, at 2 or 3 meters 

 the outlines are, hazy. The normal living eye is, however, 

 able to give one the sensation of a clear image at any distance 

 from several inches to several miles. That there is actually 

 a sharply defined image upon the retina when the normal 

 mind has the sensation of such an image there is no doubt. 

 One knows from his experience with optical instruments 

 that they must be readjusted for each distance if they are 

 to yield a sharp image for each distance. 



The same thing is true in the case of the organic optical 

 instruments with which one perceives the form, color and 

 space relations of the objects of his environment. The 

 functional adaptation of the visual organs to distance is called 

 accommodation . 

 a. Accommodation. 

 Experiments and Observations. 



(1) Take a sharp pointed pencil or similar object in each 

 hand; hold the upturned points in the line of direct 

 vision before the eye, one point being about 25 centi- 

 meters distant from the eye and the other at arm's 

 length; make the observations with one eye, the other 

 being closed or screened, 

 (0) Focus upon the near point. Is the image of the 



distant point clear? 



() Focus upon the distant point. Is the image of 

 the near point clear? 



216 



