Page:Popular Science Monthly Volume 2.djvu/552

532 and slacken the circulation in almost every case: if they are intense, they even effect its complete check by a strong contraction of the little arterial branches. Continuous currents do not act in this way; usually they quicken the circulation, while occasioning an enlargement of the vessels, at least, this has been established by Robin and Hiffelsheim, in the microscopic examination of the flow of blood under electric stimulus. Onimus and Legros afterward proved that these movements are governed by the following law: The descending current dilates the vessels, and the ascending current contracts them. A striking experiment proves the value of this law: A part of the skull of a vigorous dog is removed, so as to expose the brain. The positive pole of a pretty strong battery is then placed on the exposed brain, and the negative pole on the neck. The slender and superficial vessels of the brain contract visibly, and the organ itself seems to collapse. Arranging the poles in the contrary order, the reverse is remarked; the capillary vessels swell and distend, while the substance of the brain protrudes through the opening made in the walls of the skull. This experiment proves the possibility of increasing or lessening at will the intensity of circulation in the brain, as indeed in any other organ, by means of electric currents. Onimus lately made an equally interesting experiment. Many persons know that the famous physiologist Helmholz introduced into medicine the use of a simple and convenient instrument called the ophthalmoscope, by means of which the bottom of the eye may be quite distinctly seen, that is to say, the net formed by the nerve-fibres, and the delicate vessels of the retina. Now, on examining this net, while the head is put under electric influence, the little blood-tubes are plainly seen to dilate and grow of a more lively crimson.

Let us now study the effect of the electric current on the functions of the motor system, and on sensibility. Aldini, a nephew of Galvani, undertook the first investigations of this kind upon human beings. Convinced that the proper study of the effects of electricity on the organs required the human body to be taken at the immediate instant after the extinction of life, he believed he would do well, as he relates himself, to take his place beside the scaffold, and under the axe of the law, to receive from the executioner's hand the blood-stained bodies which were the only really suitable subjects for his experiments. In January and February, 1802, he availed himself of the occasion of the beheading at Boulogne of two criminals, whom the government willingly gave up to his scientific inquiry. Subjected to electric action, these bodies presented so strange a sight as to terrify some of the assistants. The muscles of the face contracted in frightful grimaces. All the limbs were seized with violent convulsions. The bodies seemed to feel the first stir of resurrection, and an impulse to spring up. For several hours after decapitation, the vital centres of movement retained the power of answering to the electric