Chap. VI. WEEPIXG. 171 



converge. 23 Every one knows how irresistibly the eye- 

 brows are drawn down under an intensely bright light. 

 The eyelids also involuntarily wink when an object is 

 moved near the eyes, or a sound is suddenly heard. The 

 well-known case of a bright light causing some persons 

 to sneeze is even more curious; for nerve-force here radi- 

 ates from certain nerve-cells in connection with the 

 retina, to the sensory nerve-cells of the nose, causing 

 it to tickle; and from these, to the cells which command 

 the various respiratory muscles (the orbiculars included) 

 which expel the air in so peculiar a manner that it rushes 

 through the nostrils alone. 



To return to our point: why are tears secreted during 

 a screaming-fit or other violent expiratory efforts? As 

 a slight blow on the eyelids causes a copious secretion 

 of tears, it is at least possible that the spasmodic con- 

 traction of the eyelids, by pressing strongly on the eye- 

 ball, should in a similar manner cause some secretion. 

 This seems possible, although the voluntary contraction 

 of the same muscles does not produce any such effect. 

 "We know that a man cannot voluntarily sneeze or cough 

 with nearly the same force as he does automatically: and 

 so it is with the contraction of the orbicular muscles: 

 Sir C. Bell experimented on them, and found that by 

 suddenly and forcibly closing the eyelids in the dark, 

 sparks of light are seen, like those caused by tapping 

 the eyelids with the fingers; " but in sneezing the com- 

 pression is both more rapid and more forcible, and the 

 sparks are more brilliant." That these sparks are due 

 to the contraction of the eyelids is clear, because if they 

 " are held open during the act of sneezing, no sensation 

 of light will be experienced." In the peculiar cases re- 



23 See, on these several points, Prof. Donders ' On the 

 Anomalies of Accommodation and Pcefraction of the Eye,' 

 1864, p. 573. 



