retrograde impulse communicated to the blood in the veins at that time.
When we contract the chest and expel the air, there is a retardation of
the blood in the veins of the neck and head; and in the more powerful
acts of expulsion, the blood not only distends the vessels, but is even
regurgitated into the minute branches. Were the eye not properly
compressed at that time, and a resistance given to the shock,
irreparable injury might be inflicted on the delicate textures of the
interior of the eye. He further adds, If we separate the eyelids of a
child to examine the eye, while it cries and struggles with passion, by
taking off the natural support to the vascular system of the eye, and
means of guarding it against the rush of blood then occurring, the
conjunctiva becomes suddenly filled with blood, and the eyelids
everted.
Not only are the muscles round the eyes strongly contracted, as Sir C.
Bell states and as I have often observed, during screaming, loud
laughter, coughing, and sneezing, but during several other analogous
actions. A man contracts these muscles when he violently blows his
nose. I asked one of my boys to shout as loudly as he possibly could,
and as soon as he began, he firmly contracted his orbicular muscles; I
observed this repeatedly, and on asking him why he had every time so
firmly closed his eyes, I found that he was quite unaware of the fact:
he had acted instinctively or unconsciously.
It is not necessary, in order to lead to the contraction of these
muscles, that air should actually be expelled from the chest; it
suffices that the muscles of the chest and abdomen should contract with
great force, whilst by the closure of the glottis no air escapes. In
violent vomiting or retching the diaphragm is made to descend by the
chest being filled with air; it is then held in this position by the
closure of the glottis, as well as by the contraction of its own
fibres. [613] The abdominal muscles now contract strongly upon the
stomach, its proper muscles likewise contracting, and the contents are
thus ejected. During each effort of vomiting the head becomes greatly
congested, so that the features are red and swollen, and the large
veins of the face and temples visibly dilated. At the same time, as I
know from observation, the muscles round the eyes are strongly
contracted. This is likewise the case when the abdominal muscles act
downwards with unusual force in expelling the contents of the
intestinal canal.
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