[13] See Dr. Brinton's account of the act of vomiting, in Todd's Cyclop.
of Anatomy and Physiology, 1859, vol. v. Supplement, p. 318.

The greatest exertion of the muscles of the body, if those of the chest are
not brought into strong action in expelling or compressing the air within
the lungs, does not lead to the contraction of the muscles round the eyes.
I have observed my sons using great force in gymnastic exercises,
as in repeatedly raising their suspended bodies by their arms alone,
and in lifting heavy weights from the ground, but there was hardly any
trace of contraction in the muscles round the eyes.

As the contraction of these muscles for the protection
of the eyes during violent expiration is indirectly,
as we shall hereafter see, a fundamental element in several
of our most important expressions, I was extremely anxious
to ascertain how far Sir C. Bell's view could be substantiated.
Professor Donders, of Utrecht,[14] well known as one of the highest
authorities in Europe on vision and on the structure of the eye,
has most kindly undertaken for me this investigation with
the aid of the many ingenious mechanisms of modern science,
and has published the results.[15] He shows that during
violent expiration the external, the intra-ocular, and the
retro-ocular vessels of the eye are all affected in two ways,
namely by the increased pressure of the blood in the arteries,
and by the return of the blood in the veins being impeded.
It is, therefore, certain that both the arteries and the veins
of the eye are more or less distended during violent expiration.
The evidence in detail may be found in Professor Donders'