582 STUDIES IN ADVANCED PHYSIOLOGY. 



From these figures it will be seen that only one point 

 can be seen single at one time; all other points appear 



C 9, 92" " . T3 



Fig. 181. Fig. 182. 



Figs. 181 and 182. DIAGRAMS TO SHOW THE ORIGIN OF DOUBLE VISION. 



more or less distinctly double. We are not aware of the 

 doubleness of these outside-lying points for the following 

 reasons: 



First. To see an object clearly we turn to it the yellow 

 spots of both eyes, which are corresponding points. Hence 

 all objects seen distinctly, that is, with the yellow spot, 

 appear single. 



Second. The other portions of the retina are not so sen- 

 sitive as the yellow spot, and so the doubleness of the 

 image does not press itself into the field of consciousness. 



Third . Attention is usually riveted to those objects only 

 which fall in or very close to the yellow spot, and we do 

 not take cognizance of objects falling on the periphery of 



