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. Bowman, we have seen that some weeks after the eye has been
very slightly injured, spasmodic contractions of the eyelids ensue,
and these are accompanied by a profuse flow of tears.
In the act of yawning, the tears are apparently due solely
to the spasmodic contraction of the muscles round the eyes.
Notwithstanding these latter cases, it seems hardly credible
that the pressure of the eyelids on the surface of the eye,
although effected spasmodically and therefore with much greater
force than can be done voluntarily, should be sufficient to cause
by reflex action the secretion of tears in the many cases
in which this occurs during violent expiratory efforts.


[23] See, on these several points, Prof. Donders `On the Anomalies
of Accommodation and Refraction of the Eye,' 1864, p. 573.