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- 

