about. Their size is now 1⁄20000 of an inch, and they finally attain a length of 1⁄6400 of an inch." These long vibrios are gradually changed into cells, which Dr. Calvert calls mierozyms, the first step in transformation being their division into two independent bodies. An extremely faint line appears across the animalcule's centre, increasing in distinctness until the vibrio looks like two individuals joined together. Then they separate, acquiring each an independent existence. The parts again divide and subdivide, until they appear to be no more than cells endowed with great natatory power. In twelve months or so the vibrios disappear, being succeeded by mierozyms, either in motion or at rest. If these latter be placed in a solution of fresh albumen, vibrios are abundantly developed, apparently because they have now all the circumstances favorable to their growth and reproduction.
Experiments on the Circulation of the Frog.—Certain drugs, such as digitalis, veratrum, and ergot, when taken into the system, are known to exert a powerful influence on the apparatus of circulation, and, on this account, are largely employed by physicians as medicinal agents. In order to learn something further of the manner in which they act, Dr. Boldt has been studying the effects produced by their active principles when thrown into the circulation of the frog. Curarized frogs had the intestines and mesentery exposed, so that the movement of the blood in these parts could be readily watched through the microscope. Twelve experiments with digitalin, injected hypodermically, showed that it produces a strong contraction of the peripheral vessels, which is followed by a marked slowing of the pulse, and this, if the dose be large enough, by laming of the heart, as shown by smallness, irregularity, and rapidity of the pulse, with a vibrating or undulating blood-stream; finally, after a short increase in rapidity, the pulse falls with great suddenness, and then, with general vaso-motor paralysis, the animal dies. Eleven experiments with veratrin showed that it directly paralyzes heart and arterial muscles, there being an immediate lowering of the pulse-frequency, the size and force of its wave, and an increase in the lumen of the vessels. Twelve experiments with ergotin resulted in a constant lowering of the pulse-rapidity, by both large and small doses, accompanied by peristaltic or wave-like contractions and expansions of the artery.
Paper Car-Wheels.—Car-wheels of paper, though universally admitted to be superior to those of iron or steel, have not been much used hitherto, owing to their high price. If, however, as is claimed, paper wheels are more durable than those of other materials, and if they do less injury to the tracks, besides being safer and more noiseless, it may in the end be found economical to employ them. The Connecticut River Railroad, as we learn from the Iron Age, is about to give these wheels a practical trial, having ordered a set of them for the forward truck of a locomotive. The process of manufacturing wheels of paper is as follows: A number of sheets of common straw-paper are compacted together under a pressure of 350 tons. The mass is then turned perfectly round, and the hub forced into a hole in the centre. The tire, which is of steel, has a bevel of one-quarter of an inch on the inside edge, and the paper filling is forced in under a pressure of 250 tons. Two iron disks, one on either side, and bolted together, keep the filling from coming out; but, as the tire bears on the paper and not on the disks, the wheel partakes of the elasticity of the former.
Biela's Comet.—Arago, to quiet all apprehensions of a collision of the earth with Biela's comet, made an accurate calculation of its orbit and periods, and so showed that such a catastrophe could not occur for thousands or even millions of years. But, as Prof. Daniel Kirk wood shows, in the Journal of the Franklin Institute, the break-up of that comet, which was observed in January, 1846, very materially alters the conditions of the problem, and now Prof. Kirkwood announces the latter end of November, 1892, as the time when, in all probability the earth and the comet will come in collision. The comet's period is about six years and eight months. After the break-up of January, 1846, it reappearance in