Electro-physiology and electro-therapeutics : showing the best methods for the medical uses of electricity / By Alfred C. Garratt.

to be affected on the same side ; and so it is always found: the pupil on that side is dilated, and seen to he larger than the pupil on the unaffected side of the body. Besides, it is not necessary to apply the galvanic current to the eye at all in order to produce this luminous flash or spark ; nor yet is it required that some branches of the trigeminal should be embraced by the electrodes. Through the mysteries of reflex action, this phe- nomenon is frequently produced while operating with galvanic currents about the branches of the cervical ganglia in the neck, as also about the head while treating for crown headache, or for nervous deafness, or contractions of the occipital portions of the trapezius. Indeed, this was noticed long ago ; for Dr. Achard, of Berlin, by actual experiment, found, " that if one pole of a considerable voltaic pile was placed in the mouth, and the other in the rectum, there was seen a flash of lightning" at every closure and opening of the chain.* (See p. 641.) But if the wet sponge electrode is pressed upon the closed eyelid, while the other electrode is on the upper part of the spine, then at every sudden application, variation, or interrup- tion of the active galvanic current, the flash will appear; and the degree of this is in ratio with the intensity of the current employed, and inversely to the resistance, or failure of in- working. This flash evidently results from a direct electric excitement of the retina. If the positive pole is over the eye, the flash is purple or bluish ; but if the negative pole is there, then the flash is a pale reddish yellow, or an orange-colored light is seen. These luminous flashes are the brightest at the circumference when the negative polo is to the eye, but the lightning flash is uniform when the positive pole is placed there. The Iris. — If we direct one pole of a very moderate electro- magnetic or galvanic current to the most prominent portion of the cornea, while the other electrode is placed upon the face, the circular fibres of the iris are seen to contract, not slowly, but most promptly, much as do voluntary muscles; and when the * Versuche Uber die Gereizte Muskel undNervenfacer, by Von Alexander Humboldt. Berlin, 1797, toI. i. p. 334.