PHYSIOLOGICAL PARADOXES. 



especially at its centre, where there is a small 

 central hollow (the fovea centralist, is the part 

 of the retina which is most sensitive to light, 

 and so we turn it directly opposite the incident 

 rays from the object at which we desire to 

 look directly. 



But other parts of the retina also are sen- 



M.L 



O.N 



L.E. 



F R.E 



FlG. 46.-EXPLANATION OF BLIND-SPOT EXPERIMENT. 



sitive, though less keenly so. Consequently the 

 light from objects at the side, as D and L, pro- 

 duces images, though less distinct ones, at the 

 points marked by the ends of the lines from 

 F and N ; and this is how we are enabled to see 

 things which are out of the line of direct vision. 

 Now, it can be seen from the dotted lines 

 that the light from the three L's strikes the 

 retina in three different places if the retina be 

 kept unmoved by keeping the macula lutea 



218 



