The Expression of Emotion in Man and Animals by Charles Darwin (adult books to read TXT) 📕

Yawning commences with a deep inspiration, followed by a long and forcible expiration; and at the same time almost all the muscles of the body are strongly contracted, including those round the eyes.

During this act tears are often secreted, and I have seen them even rolling down the cheeks.

I have frequently observed that when persons scratch some point which itches intolerably, they forcibly close their eyelids; but they do not, as I believe, first draw a deep breath and then expel it with force; and I have never noticed that the eyes then become filled with tears; but I am not prepared to assert that this does not occur.

The forcible closure of the eyelids is, perhaps, merely a part of that general action by which almost all the muscles of the body are at the same time rendered rigid. It is quite different from the gentle closure of the eyes which often accompanies, as Gratiolet remarks,[19]

the smelling a delicious odour, or the tasting a delicious morsel, and which probably originates in the desire to shut out any disturbing impression through the eyes.

[19] `De la Physionomie,’ 1865, p. 217.

Professor Donders writes to me to the following effect: “I have observed some cases of a very curious affection when, after a slight rub (_attouchement_), for example, from the friction of a coat, which caused neither a wound nor a contusion, spasms of the orbicular muscles occurred, with a very profuse flow of tears, lasting about one hour. Subsequently, sometimes after an interval of several weeks, violent spasms of the same muscles re-occurred, accompanied by the secretion of tears, together with primary or secondary redness of the eye.”

Mr. Bowman informs me that be has occasionally observed closely analogous cases, and that, in some of these, there was no redness or inflammation of the eyes.

I was anxious to ascertain whether there existed in any of the lower animals a similar relation between the contraction of the orbicular muscles during violent expiration and the secretion of tears; but there are very few animals which contract these muscles in a prolonged manner, or which shed tears. The Macacus maurus, which formerly wept so copiously in the Zoological Gardens, would have been a fine case for observation; but the two monkeys now there, and which are believed to belong to the same species, do not weep.

Nevertheless they were carefully observed by Mr. Bartlett and myself, whilst screaming loudly, and they seemed to contract these muscles; but they moved about their cages so rapidly, that it was difficult to observe with certainty. No other monkey, as far as I have been able to ascertain, contracts its orbicular muscles whilst screaming.

The Indian elephant is known sometimes to weep. Sir E. Tennent, in describing these which he saw captured and bound in Ceylon, says, some “lay motionless on the ground, with no other indication of suffering than the tears which suffused their eyes and flowed incessantly.”

Speaking of another elephant he says, “When overpowered and made fast, his grief was most affecting; his violence sank to utter prostration, and he lay on the ground, uttering choking cries, with tears trickling down his cheeks.”[20] In the Zoological Gardens the keeper of the Indian elephants positively asserts that he has several times seen tears rolling down the face of the old female, when distressed by the removal of the young one. Hence I was extremely anxious to ascertain, as an extension of the relation between the contraction of the orbicular muscles and the shedding of tears in man, whether elephants when screaming or trumpeting loudly contract these muscles. At Mr. Bartlett’s desire the keeper ordered the old and the young elephant to trumpet; and we repeatedly saw in both animals that, just as the trumpeting began, the orbicular muscles, especially the lower ones, were distinctly contracted.

On a subsequent occasion the keeper made the old elephant trumpet much more loudly, and invariably both the upper and lower orbicular muscles were strongly contracted, and now in an equal degree.

It is a singular fact that the African elephant, which, however, is so different from the Indian species that it is placed by some naturalists in a distinct sub-genus, when made on two occasions to trumpet loudly, exhibited no trace of the contraction of the orbicular muscles.

[20] `Ceylon,’ 3rd edit. 1859, vol. ii. pp. 364, 376.

I applied to Mr. Thwaites, in Ceylon, for further information with respect to the weeping of the elephant; and in consequence received a letter from the Rev. Mr Glenie, who, with others, kindly observed for me a herd of recently captured elephants.

These, when irritated, screamed violently; but it is remarkable that they never when thus screaming contracted the muscles round the eyes.

Nor did they shed tears; and the native hunters asserted that they had never observed elephants weeping. Nevertheless, it appears to me impossible to doubt Sir E. Tennent’s distinct details about their weeping, supported as they are by the positive assertion of the keeper in the Zoological Gardens. It is certain that the two elephants in the Gardens, when they began to trumpet loudly, invariably contracted their orbicular muscles.

I can reconcile these conflicting statements only by supposing that the recently captured elephants in Ceylon, from being enraged or frightened, desired to observe their persecutors, and consequently did not contract their orbicular muscles, so 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 case given by Sir Charles Bell, `Philosophical Transactions,’ 1823, p. 177.

As soon as by this, or by some other means, a reflex action of this nature had been established and rendered easy, other stimulants applied to the surface of the eye—such as a cold wind, slow inflammatory action, or a blow on the eyelids—

would cause a copious secretion of tears, as we know to be the case.

The glands are also excited into action through the irritation of adjoining parts. Thus when the nostrils are irritated by pungent vapours, though the eyelids may be kept firmly closed, tears are copiously secreted; and this likewise follows from a blow on the nose, for instance from a boxing-glove. A stinging switch on the face produces, as I have seen, the same effect.

In these latter cases the secretion of tears is an incidental result, and of no direct service. As all these parts of the face, including the lacrymal glands, are supplied with branches of the same nerve, namely, the fifth, it is in some degree intelligible that the effects of the excitement of any one branch should spread to the nerve-cells or roots of the other branches.

The internal parts of the eye likewise act, under certain conditions, in a reflex manner on the lacrymal glands. The following statements have been kindly communicated to me by Mr. Bowman; but the subject is a very intricate one, as all the parts of the eye are so intimately related together, and are so sensitive to various stimulants.

A strong light acting on the retina, when in a normal condition, has very little tendency to cause lacrymation; but with unhealthy children having small, old-standing ulcers on the cornea, the retina becomes excessively sensitive to light, and exposure even to common daylight causes forcible and sustained closure of the lids, and a profuse flow of tears. When persons who ought to begin the use of convex glasses habitually strain the waning power of accommodation, an undue secretion of tears very often follows, and the retina is liable to become unduly sensitive to light.

In general, morbid affections of the surface of the eye, and of the ciliary structures concerned in the accommodative act, are prone to be accompanied with excessive secretion of tears.

Hardness of the eyeball, not rising to inflammation, but