Page:Popular Science Monthly Volume 5.djvu/782

762 toward the East. In 1859 it had reached within a hundred miles of Omaha. In 1861 it had entered Iowa, and in 1865 had crossed the Mississippi into Illinois, Thus on it moved eastward, generally at about fifty miles a year, though latterly the movement must have been more rapid. The sad thing is, that every swarm that moves leaves a permanent colony behind.

Every device has been employed to destroy them. Paris-green has been dusted on the plants. This will kill all it touches. But its application is expensive, and not without danger. It was found necessary to use an ingenious machine drawn by two horses. This consisted of a large box supported by wheels. The box was open at the top, over which was a revolving flapper, or fan, that brushed the vines over the box, at the same time striking them, thus causing the beetles to fall to the bottom of the box, where was a pair of revolving rollers, between which they were crushed. There were other kinds of machines, but this was the most effective.

The Colorado beetle is about half an inch long, roundish, and in form much like a lady-bug. It has a series of ten stripes on each wing-cover, being alternately brown and yellow. It is a very beautiful insect; but, alas! it is among the most formidable of those diminutive enemies of the industry of man, whose depredations, even in the brief history of our nation, has cost us, in money loss of crops, more by many times than the sum-total of all our wars. Already, in Maryland, the ravages of the new-comer are filling the farmers with dismay.

Prof. Morse on the North American Unionidæ.—In his paper on this subject, at the recent meeting of the American Association, Prof. Morse explained, on the theory of natural selection, why the fresh-water mussels are so much more abundant in this country than in Europe, and why they are so much more numerous west of the Alleghanies than on their eastern slope. The families of fresh-water mollusks are few in number, and are intimately related with those families in the sea that have proved capable of surviving admixture with fresh water, and that commonly occur between high and low water mark. Many animals have adapted themselves to the changing influences which are liable to occur between high and low water mark, such as inundations, fresh water, and rain. Others have adapted themselves to brackish water, and, to those forms that have survived, the freshwater mollusks are closely related. In this struggle for adaptation to new conditions, great modification of form takes place, a fact illustrated and confirmed by what has been observed in the case of the mya or common clam. This belongs between high and low water, and, although never yet so far changed as to live in fresh water, it has passed through almost innumerable modifications of form before giving up the struggle. Now, referring to the past geological history of this continent, we find, from the successive upheavals of the Laurentian hills to the North, the Alleghanies on the East, and the Sierras on the West, a gradual inclosing of wide inland seas, lagoons, whose drainage must have been toward the Mississippi Valley. These, in their gradual transition from briny to fresh water, would furnish all the conditions favorable to a transformation from marine to fresh water species; to be followed by an infinite number of fresh-water forms, according as the subsequent conditions varied.

Use of the Actual Cautery.—The "actual cautery" is commonly defined to be a red-hot iron used for burning or disorganizing the parts to which it is applied. The application of a red-hot iron directly to the living tissues is justly regarded as an extremely painful operation; but, if the iron be heated to a white heat, it is absolutely painless. The difference between the two is analogous to the difference between a bullet speeding at its maximum velocity, which may produce mortal injury without pain, and a nearly-spent bullet, which slowly lacerates the tissues and causes agony. Dr. J. S. Camden, writing in the Medical Times and Gazette, recites as follows his own experience with cauteries at different degrees of heat: "When actual cautery," says he, "is to be used, the iron must be heated till it is really of a white heat, and looks almost as white as white paper. If then applied it destroys the part instantaneously, giving no pain; but it must be removed quickly on the heat