Page:Popular Science Monthly Volume 5.djvu/521

Rh becomes intensely heated. "The quivering of the air over hot ground foreshadows the whirlwind as mirage does the simoom, and sultry heat and oppressive calm do the hurricane." In the stratum of heated air next the ground resides the energy which produces the whirlwind. That this, in many instances, is prevented from rising, has been proved by numerous observations. At last the upward tendency becomes so strong that it breaks through the overlying heavier air, and there occurs an upward discharge, followed by all the phenomena of whirlwinds.

Dupuy on the Functions of the Brain.—Dr. Eugène Dupuy, of Paris, has repeated Ferrier's experiments on the brain, with results which do not accord with those of the English physiologist. In the for December last we gave an account of Ferrier's researches, and hence it will suffice to say here that in his experiments stimulation of the superior external convolution of the brain produced movement of the animal's paw; of the mid-frontal region, contraction of the eyelid; of the parietal region, movement of the ear; of the lower frontal and orbital regions, movement of the tongue. He therefore concludes that in these regions there are actual centres for the movements obtained. Dupuy, on the other hand, wherever the electrodes were placed, whether on the frontal, parietal, or orbital convolutions, succeeded only in obtaining, on slight stimulation, movements of the opposite fore-paw, which, on stronger stimulation, extended to the whole of that side of the body. Further, the electrodes applied to the uninjured surface of the dura mater over the convolutions produced the same effect as when placed on the exposed convolutions themselves.

Dupuy was led to suspect that the electrical stimulation might in these cases be so diffused through the whole hemisphere as to affect directly the base of the brain or even the nerves arising there. To ascertain the truth of this matter he laid bare one-half of the brain of a dog, under complete anæsthesia, and applied to the posterior extremity of the hemisphere the nerve of a galvanoscopic frog, duly insulated. The electrodes were then placed on the front of the hemisphere, and movements produced in the opposite fore-paw, the legs of the frog being simultaneously thrown into violent contraction. Upon another dog, under partial anæsthesia, he divided the corpus striatum and optic thalamus on one side, the corpus callosum having previously been cut through. The electrodes were then placed on the convolutions above and behind the Sylvian fissure. With a strong current, not only the fore-leg of the opposite side, but also the hind-leg, exhibited contraction. In another experiment he removed the whole cerebral mass above the pons Varolii, and applied the electrodes to the cut surface; muscular contractions resulted, limited to the fore-limbs, right and left. These results, many times obtained, render it certain, according to Dr. Dupuy, that electrical stimulation, to whatever part of the brain it may be applied, is widely diffused; and that such diffused stimulation, reaching the base, and there affecting the nuclei, the medulla, or the nerves themselves, will explain all the phenomena obtained by Ferrier and by himself on faradizing the convolutions.

The Sponge-Fisheries.—The chief industry of the Sporades Islands, in the Grecian Archipelago, is the sponge-fishery. The yearly average crop of sponges is estimated at £120,000 sterling. The diving-apparatuses used in the fishery are imported exclusively from England and France. Though there is no difference in construction between English and French machines, with regard to the depth they can attain, or the length of time a diver can remain under water, still English apparatus generally proves stronger, and the gears are of superior quality. The air-tubes, however, have hitherto labored under the disadvantage of being heavier than the French, thus impeding the free movements of the diver, the tubes being caught among the rocks. But, samples of French floating tubes having been sent to England, the result has already been a great improvement in the manufacture of the English article. A common fraud practised by traders in rough sponges is to introduce into them a quantity of sand, so as to add to their weight. In order to guard against this, agents are now sent to Rhodes, which is the centre of this commerce, to purchase the sponge