[14] I am greatly indebted to Mr. Bowman for having introduced me to Prof. Donders, and for his aid in persuading this great physiologist to undertake the investigation of the present subject. I am likewise much indebted to Mr. Bowman for having given me, with the utmost kindness, information on many points.
[15] This memoir first appeared in the `Nederlandsch Archief voor Genees en Natuurkiinde,' Deel 5, 1870. It has been translated by Dr. W. D. Moore, under the title of "On the Action of the Eyelids in determination of Blood from expiratory effort," in `Archives of Medicine,' edited by Dr. L. S. Beale, 1870, vol. v. p. 20.
With respect to the protection of the eye during violent expiratory efforts by the pressure of the eyelids, Professor Donders concludes from his various observations that this action certainly limits or entirely removes the dilatation of the vessels.[16] At such times, he adds, we not unfrequently see the hand involuntarily laid upon the eyelids, as if the better to support and defend the eyeball.
[16] Prof. Donders remarks (ibid. p. 28), that, "After injury to the eye, after operations, and in some forms of internal inflammation, we attach great value to the uniform support of the closed eyelids, and we increase this in many instances by the application of a bandage. In both cases we carefully endeavour to avoid great expiratory pressure, the disadvantage of which is well known." Mr. Bowman informs me that in the excessive photophobia, accompanying what is called scrofulous ophthalmia in children, when the light is so very painful that during weeks or months it is constantly excluded by the most forcible closure of the lids, he has often been struck on opening the lids by the paleness of the eye,-- not an unnatural paleness, but an absence of the redness that might have been expected when the surface is somewhat inflamed, as is then usually the case; and this paleness he is inclined to attribute to the forcible closure of the eyelids.
Nevertheless much evidence cannot at present be advanced to prove that the eye actually suffers injury from the want of support during violent expiration; but there is some. It is "a fact that forcible expiratory efforts in violent coughing or vomiting, and especially in sneezing, sometimes give rise to ruptures of the little (external) vessels" of the eye.[17] With respect to the internal vessels, Dr. Gunning has lately recorded a case of exophthalmos in consequence of whooping-cough, which in his opinion depended on the rupture of the deeper vessels; and another analogous case has been recorded. But a mere sense of discomfort would probably suffice to lead to the associated habit of protecting the eyeball by the contraction of the surrounding muscles. Even the expectation or chance of injury would probably be sufficient, in the same manner as an object moving too near the eye induces involuntary winking of the eyelids. We may, therefore, safely conclude from Sir C. Bell's observations, and more especially from the more careful investigations by Professor Donders, that the firm closure of the eyelids during the screaming of children is an action full of meaning and of real service.
We have already seen that the contraction of the orbicular muscles leads to the drawing up of the upper lip, and consequently, if the mouth is kept widely open, to the drawing down of the corners by the contraction of the depressor muscles. The formation of the naso-labial fold on the cheeks likewise follows from the drawing up of the upper lip. Thus all the chief expressive movements of the face during crying apparently result from the contraction of the muscles round the eyes. We shall also find that the shedding of tears depends on, or at least stands in some connection with, the contraction of these same muscles.
[17] Donders, ibid. p. 36.
In some of the foregoing cases, especially in those of sneezing and coughing, it is possible that the contraction of the orbicular muscles may serve in addition to protect the eyes from too severe a jar or vibration. I think so, because dogs and cats, in crunching hard bones, always close their eyelids, and at least sometimes in sneezing; though dogs do not do so whilst barking loudly.