164 NATURE AND LIFE. 



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 estab- 

 lished by Robin and Hiffelsheim, in the microscopic exami- 

 nation 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 nega- 

 tive 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 Helmholtz 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. Al- 

 dini, 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 re- 



