On the physiological action of light : abstract of three communications read before the Royal Society of Edinburgh / by James Dewar and John G. M'Kendrick.

  • Dewar, James, Sir, 1842-1923.
Date:
[1873?]
Catalogue details

Licence: Public Domain Mark

Credit: On the physiological action of light : abstract of three communications read before the Royal Society of Edinburgh / by James Dewar and John G. M'Kendrick. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    ] 2 tance of about twenty-six inches. Light produced a variation in this deflection of about 60 degrees,—that is, about ten percent., the largest amount of variation we have yet observed in any eye. It was also demonstrated that the effect of light, dimin- ished in intensity by distance, was exactly what was observed in the case of the simple eye. For example, at the distance of one foot, a variation to the extent of about 100 degrees was observed. At a distance of ten feet, with l-100th part of the amount of light, the effect was not 1 degree, but 20 degrees, or one-fifth of the total amount observed at one foot. 2. The action of light on the electro-motive force of the living eye in cats and birds (pigeon and owl) has been observed. In our earlier experiments, we found great difficulty in observ- ing sensitiveness to light in the eyes of mammals and birds, when these were removed with the utmost despatch from the orbit of the animal immediately after death. This was evi- dently owing to the fact, that the sensibility of the nervous system in these animals disappears quickly after the withdrawal of healthy blood. It, therefore, became necessary to perform the experiment on the living animal. This was done by first putting the cat or bird under the influence of chloroform, then fixing it by a proper apparatus so that the head was perfectly immoveable, and lastly removing the outer wall of the orbit with as little disturbance to the ciliary vessels as possible. The optic nerve was now cut, the transverse section directed upwards, and the clay points of the electrodes were now adjusted, one to the transverse section of the nerve, and the other to the cornea. With these arrangements, we at once found a strong current extremely sensitive to light. 4. The effect was traced into the optic lobes of a living pigeon under chloroform. The following were the results of this observation:—a. When one pole was applied to the left optic lobe, and the other to the cornea of the right eye, a deflection was obtained which was sensitive to light; b. When the pole was removed from the right eye and applied to the cornea of the left, a smaller deflection was obtained, also