Valentin on the functions of the nerves of the orbit / translated from the Latin by John F. France.
- Gabriel Valentin
- Date:
- [1846]
Licence: Public Domain Mark
Credit: Valentin on the functions of the nerves of the orbit / translated from the Latin by John F. France. Source: Wellcome Collection.
10/40 (page 6)
![is such that, taking their size into consi¬ deration, they could hardly be recog¬ nised distinctly with our microscopes : possibly they may be external portions of the hyaloid membrane. I see the blood-vessels in front of the retina subjectively in two ways ; as the figure of a vein, in the manner described by Purkinje ; or, by the motion of the blood. The venous figure* arises imme¬ diately in my left myopic eye ; and its rarnilications extending to the smallest offsets, are so clear and perfect, that no one, who has ever seen an injection of the central vein, could have the least doubt of their identity. The point of entrance of the optic nerve and the foramen centrale appear round and grey; and on continuing the experi¬ ment longer, I see the elevated fold in which the limbus luteus foramen centrale are situated; it appears raised, and of a milky grey, but 1 have never perceived any trace of the limbus luteus itself. In the subjective phenomenon of the circulation, circular molecules, like the corpuscles of the blood, appear; and their motion resembles to a certain extent that of the blood as seen be¬ neath the microscope ; yet I have never distinguished a nucleus, and they can scarcely he regarded as blood-corpus¬ cles, since they are not pale, or black, like other parts lying upon the retina, seen in subjective vision, but lumi- nousf. I know no means of exciting this appearance voluntarily, in my own person; but it takes place, at certain times, if I throw the flame of a candle suddenly on the eyes; or, if after hav¬ ing been some time in a room lighted by a single candle only, I purposely and fixedly regard the flame. Then, on the grey ground surrounding the flame, these molecules appear, floating and moving rapidly from place to place, shining grey in colour, circular and flat in form ; so that they resemble * In the “Repertorium,” vol. i. I have com¬ municated the fact that the tortuous course of the vena centralis retina can be observed in this way in the living sidyect. If this venous tigure ap¬ pears luminous sometimes, as on immersing' the head suddenly in cold water, according to the observations of Purkinje and Muller, it is because the over-distended blood vessels compress the retina, each in form of its own outline. t It is difficult, and, imbed, impossible, to suppose that each molecide of the blood can, by pressure, stimidate the retina to luminous sub¬ jective action, as the over-distended vessels do. to a certain extent the molecules of the blood; but their motion is neither al¬ tered nor disturbed by movement of the eye itself. I have never noticed the caudate sparks said to be seen on bend¬ ing the head downwards too long; but separate, straight, or curved lines, have made their appearance, which might not inaptly be compared to portions of the papillary stratum of the retina. Not uncommonly, after sudden compression of the eye with the fingers or lids, or on keeping the latter too long closed, I see a luminous stellate figure : this is no doubt the expansion of the fibres of the optic nerve into the retina ; for there is a dark round centre —corresponding with the point of en¬ trance of the nerve-encompassed by a circular rim, from which the rays proceed, and which answers to its mar¬ gin. The light, however, of the circle and rays varies in intensity. On closing the eyelids forcibly, I often see a most delicate capillary network, at first black, and placed on a feebly illumi¬ nated ground; then itself illuminated feebly; and this phenomenon is often succeeded by a palely luminous ve¬ nous figure : but, on such occasions, at the moment of re-opening the eye, there appears a network of capillaries of the utmost splendour and delicacy. High stimulation of the retina causes the perception of brilliant light; and a stimulus less in degree*, that of colour; the reaction of the retina, however, is so constituted, that the subjective image, following the development of the latter, exhibits the complementary colourf. For, being prepared to per¬ form its full function, and act with the force ] of complete light, the retina makes up, so to speak, with its comple¬ mentary subjective image, what in objective vision was deficient, in con¬ sequence of the impression being co¬ loured, and consequently in a certain * This is not the proper place for discussing the causes and phenomena of colour; yet it is manifest from the experiments of Smith (Fror. Not. vol. XV.) and others, that its diversities arise from variety of light in respect of quantity, not of quality. t The fact that white bodies, under certain circumstances, are followed by wh’te secondary images, and black ones by black, does not in¬ validate this law ; the circumstance arises from the retina, previously too active or too passive, prolonging its action after perfect closure of the eyes, and so producing continued, rather than secondary, complementary images.](https://iiif.wellcomecollection.org/image/b30798115_0010.jp2/full/800%2C/0/default.jpg)
