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 contraction
of the eyelids, by pressing strongly on the eyeball, 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 compression 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 referred to by Professor Donders and
Mr.
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