The Expression of the Emotions in Man and Animals

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.[622] 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. 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 implying a want of balance between the fluids poured out and again taken up by the intra-ocular vessels, is not usually attended with any lacrymation. When the balance is on the other side, and the eye becomes too soft, there is a greater tendency to lacrymation. Finally, there are numerous morbid states and structural alterations of the eyes, and even terrible inflammations, which may be attended with little or no secretion of tears. It also deserves notice, as indirectly bearing on our subject, that the eye and adjoining parts are subject to an extraordinary number of reflex and associated movements, sensations, and actions, besides those relating to the lacrymal glands. When a bright light strikes the retina of one eye alone, the iris contracts, but the iris of the other eye moves after a measurable interval of time. The iris likewise moves in accommodation to near or distant vision, and when the two eyes are made to converge.[623] Every one knows how irresistibly the eyebrows are drawn down under an intensely bright light. The eyelids also involuntarily wink when an object is moved near the eyes, or a sound is suddenly heard. The well-known case of a bright light causing some persons to sneeze is even more curious; for nerve-force here radiates from certain nerve-cells in connection with the retina, to the sensory nerve-cells of the nose, causing it to tickle; and from these, to the cells which command the various respiratory muscles (the orbiculars included) which expel the air in so peculiar a manner that it rushes through the nostrils alone. To return to our point: why are tears secreted during a screaming-fit or other violent expiratory efforts? As a slight blow on the eyelids causes a copious secretion of tears, it is at least possible that the spasmodic contraction of the eyelids, by pressing strongly on the eyeball, should in 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. Another cause may come conjointly into play. We have seen that the internal parts of the eye, under certain conditions act in a reflex manner on the lacrymal glands. We know that during violent expiratory efforts the pressure of the arterial blood within the vessels of the eye is increased, and that the return of the venous blood is impeded. It seems, therefore, not improbable that the distension of the ocular vessels, thus induced, might act by reflection on the lacrymal glands—the effects due to the spasmodic pressure of the eyelids on the surface of the eye being thus increased. In considering how far this view is probable, we should bear in mind that the eyes of infants have been acted on in this double manner during numberless generations, whenever they have screamed; and on the principle of nerve-force readily passing along accustomed channels, even a moderate compression of the eyeballs and a moderate distension of the ocular vessels would ultimately come, through habit, to act on the glands. We have an analogous case in the orbicular muscles being almost always contracted in some slight degree, even during a gentle crying-fit, when there can be no distension of the vessels and no uncomfortable sensation excited within the eyes. Moreover, when complex actions or movements have long been performed in strict association together, and these are from any cause at first voluntarily and afterwards habitually checked, then if the proper exciting conditions occur, any part of the action or movement which is least under the control of the will, will often still be involuntarily performed. The secretion by a gland is remarkably free from the influence of the will; therefore, when with the advancing age of the individual, or with the advancing culture of the race, the habit of crying out or screaming is restrained, and there is consequently no distension of the blood-vessels of the eye, it may nevertheless well happen that tears should still be secreted. We may see, as lately remarked, the muscles round the eyes of a person who reads a pathetic story, twitching or trembling in so slight a degree as hardly to be detected. In this case there has been no screaming and no distension of the blood-vessels, yet through habit certain nerve-cells send a small amount of nerve-force to the cells commanding the muscles round the eyes; and they likewise send some to the cells commanding the lacrymal glands, for the eyes often become at the same time just moistened with tears. If the twitching of the muscles round the eyes and the secretion of tears had been completely prevented, nevertheless it is almost certain that there would have been some tendency to transmit nerve-force in these same directions; and as the lacrymal glands are remarkably free from the control of the will, they would be eminently liable still to act, thus betraying, though there were no other outward signs, the pathetic thoughts which were passing through the person’s mind. As a further illustration of the view here advanced, I may remark that if, during an early period of life, when habits of all kinds are readily established, our infants, when pleased, had been accustomed to utter loud peals of laughter (during which the vessels of their eyes are distended) as often and as continuously as they have yielded when distressed to screaming-fits, then it is probable that in after life tears would have been as copiously and as regularly secreted under the one state of mind as under the other. Gentle laughter, or a smile, or even a pleasing thought, would have sufficed to cause a moderate secretion of tears. There does indeed exist an evident tendency in this direction, as will be seen in a future chapter, when we treat of the tender feelings. With the Sandwich Islanders, according to Freycinet,[624] tears are actually recognized as a sign of happiness; but we should require better evidence on this head than that of a passing voyager. So again if our infants, during many generations, and each of them during several years, had almost daily suffered from prolonged choking-fits, during which the vessels of the eye are distended and tears copiously secreted, then it is probable, such is the force of associated habit, that during after life the mere thought of a choke, without any distress of mind, would have sufficed to bring tears into our eyes. To sum up this chapter, weeping is probably the result of some such chain of events as follows. Children, when wanting food or suffering