EXPERIMENT III.
As my pupils took much interest in this research, some of them suspected that the light of the apartment might perhaps
have effaced that excited by the electricity. I therefore made the apartment entirely dark; and one of them taking a Leyden flask applied it to the point of the nose of another person with whom he was in communication, by laying hold of him with the other hand. By these means a very strong shock was given, but no flash of light was observed. This experiment was repeated, making the person who received the shock of the Leyden flask to remain some time before in the dark, that his eyes might be better enabled to perceive any faint light that might be excited: but the result was still the same. To those who refer Galvanism to the common laws of electricity, it will be difficult to comprehend the cause of the different action exercised by the latter on the organ of sight. But as it is not my intention at present to enter into any discussion on this subject, I shall leave it to philosophers to assign a reason for this phænomenon, and only observe, that the properties above indicated will be sufficient to authorize medical practitioners to prefer, in certain cases, the administration of Galvanism by the pile to that of common electricity.
Before I proceed directly to the medical administration of Galvanism to the organ of sight, I think it necessary to distinguish four classes of blind persons whose cases ought to be considered separately.
The first belongs to those who from their birth have been deprived of the valuable blessing of sight.
The second comprehends those become blind in consequence of some great læsion, or some derangement in the solids or in the fluids which constitute the mechanism of the eye.
The third, those who have become blind by some morbid action, though the mechanism of the eye has been little affected, and though no impediment has occurred but in regard to the action of the optic nerve.
The fourth class comprehends those who, though not actually deprived of sight, have it much weakened in consequence of disease, or of some other cause.
The administration of Galvanism does not hold forth much hope of a cure to persons belonging to the first two classes. I however resolved to attempt some experiments on this subject at Bologna; but though there were a great many blind in that city, I found that they had become so by the malignant influence of the small pox. This observation will, I hope, be of service to the pursuits of the celebrated Dr. Jenner, and of all those who exert themselves to promote the beneficial practice of vaccine inoculation.
Being deprived, at Bologna, of any opportunity of trying the effects of Galvanism in cases of persons born blind, I galvanised several who had lost their sight at a very early age. I first applied the Galvanism to the arms of five blind