The Expression of Emotion in Man and Animals [70]
that their vision might not be impeded. Those seen weeping by Sir E. Tennent were prostrate, and had given up the contest in despair. The elephants which trumpeted in the Zoological Gardens at the word of command, were, of course, neither alarmed nor enraged.
From the several foregoing cases with respect to Man, there can, I think, be no doubt that the contraction of the muscles round the eyes, during violent expiration or when the expanded chest is forcibly compressed, is, in some manner, intimately connected with the secretion of tears. This holds good under widely different emotions, and independently of any emotion. It is not, of course, meant that tears cannot be secreted without the contraction of these muscles; for it is notorious that they are often freely shed with the eyelids not closed, and with the brows unwrinkled. The contraction must be both involuntary and prolonged, as during a choking fit, or energetic, as during a sneeze. The mere involuntary winking of the eyelids, though often repeated, does not bring tears into the eyes. Nor does the voluntary and prolonged contraction of the several surrounding muscles suffice. As the lacrymal glands of children are easily excited, I persuaded my own and several other children of different ages to contract these muscles repeatedly with their utmost force, and to continue doing so as long as they possibly could; but this produced hardly any effect. There was sometimes a little moisture in the eyes, but not more than apparently could be accounted for by the squeezing out of the already secreted tears within the glands.
The nature of the relation between the involuntary and energetic contraction of the muscles round the eyes, and the secretion of tears, cannot be positively ascertained, but a probable view may be suggested. The primary function of the secretion of tears, together with some mucus, is to lubricate the surface of the eye; and a secondary one, as some believe, is to keep the nostrils damp, so that the inhaled air may be moist,[21] and likewise to favour the power of smelling. But another, and at least equally important function of tears, is to wash out particles of dust or other minute objects which may get into the eyes. That this is of great importance is clear from the cases in which the cornea has been rendered opaque through inflammation, caused by particles of dust not being removed, in consequence of the eye and eyelid becoming immovable.[22] The secretion of tears from the irritation of any foreign body in the eye is a reflex action;--that is, the body irritates a peripheral nerve which sends an impression to certain sensory nerve-cells; these transmit an influence to other cells, and these again to the lacrymal glands. The influence transmitted to these glands causes, as there is good reason to believe, the relaxation of the muscular coats of the smaller arteries; this allows more blood to permeate the glandular tissue, and this induces a free secretion of tears. When the small arteries of the face, including those of the retina, are relaxed under very different circumstances, namely, during an intense blush, the lacrymal glands are sometimes affected in a like manner, for the eyes become suffused with tears.
It is difficult to conjecture how many reflex actions have originated, but, in relation to the present case of the affection of the lacrymal glands through irritation of the surface of the eye, it may be worth remarking that, as soon as some primordial form became semi-terrestrial in its habits, and was liable to get particles of dust into its eyes, if these were not washed out they would cause much irritation; and on the principle of the radiation of nerve-force to adjoining nerve-cells, the lacrymal glands would be stimulated to secretion. As this would often recur, and as nerve-force readily passes along accustomed channels, a slight irritation would ultimately suffice to cause a free secretion of tears.
[21] Bergeon, as quoted in the `Journal of Anatomy and Physiology,' Nov. 1871, p. 235.
[22] See, for instance, a
From the several foregoing cases with respect to Man, there can, I think, be no doubt that the contraction of the muscles round the eyes, during violent expiration or when the expanded chest is forcibly compressed, is, in some manner, intimately connected with the secretion of tears. This holds good under widely different emotions, and independently of any emotion. It is not, of course, meant that tears cannot be secreted without the contraction of these muscles; for it is notorious that they are often freely shed with the eyelids not closed, and with the brows unwrinkled. The contraction must be both involuntary and prolonged, as during a choking fit, or energetic, as during a sneeze. The mere involuntary winking of the eyelids, though often repeated, does not bring tears into the eyes. Nor does the voluntary and prolonged contraction of the several surrounding muscles suffice. As the lacrymal glands of children are easily excited, I persuaded my own and several other children of different ages to contract these muscles repeatedly with their utmost force, and to continue doing so as long as they possibly could; but this produced hardly any effect. There was sometimes a little moisture in the eyes, but not more than apparently could be accounted for by the squeezing out of the already secreted tears within the glands.
The nature of the relation between the involuntary and energetic contraction of the muscles round the eyes, and the secretion of tears, cannot be positively ascertained, but a probable view may be suggested. The primary function of the secretion of tears, together with some mucus, is to lubricate the surface of the eye; and a secondary one, as some believe, is to keep the nostrils damp, so that the inhaled air may be moist,[21] and likewise to favour the power of smelling. But another, and at least equally important function of tears, is to wash out particles of dust or other minute objects which may get into the eyes. That this is of great importance is clear from the cases in which the cornea has been rendered opaque through inflammation, caused by particles of dust not being removed, in consequence of the eye and eyelid becoming immovable.[22] The secretion of tears from the irritation of any foreign body in the eye is a reflex action;--that is, the body irritates a peripheral nerve which sends an impression to certain sensory nerve-cells; these transmit an influence to other cells, and these again to the lacrymal glands. The influence transmitted to these glands causes, as there is good reason to believe, the relaxation of the muscular coats of the smaller arteries; this allows more blood to permeate the glandular tissue, and this induces a free secretion of tears. When the small arteries of the face, including those of the retina, are relaxed under very different circumstances, namely, during an intense blush, the lacrymal glands are sometimes affected in a like manner, for the eyes become suffused with tears.
It is difficult to conjecture how many reflex actions have originated, but, in relation to the present case of the affection of the lacrymal glands through irritation of the surface of the eye, it may be worth remarking that, as soon as some primordial form became semi-terrestrial in its habits, and was liable to get particles of dust into its eyes, if these were not washed out they would cause much irritation; and on the principle of the radiation of nerve-force to adjoining nerve-cells, the lacrymal glands would be stimulated to secretion. As this would often recur, and as nerve-force readily passes along accustomed channels, a slight irritation would ultimately suffice to cause a free secretion of tears.
[21] Bergeon, as quoted in the `Journal of Anatomy and Physiology,' Nov. 1871, p. 235.
[22] See, for instance, a