Page:Popular Science Monthly Volume 25.djvu/294

284 I infer that the theory of acetonæmia is founded on good evidence." Dr. Richardson mentions also the secondary absorption of poisonous matter from wounds, and from the abraded and ulcerating surfaces produced in diphtheria, malignant scarlet fever, etc., and concludes by saying: "Such observations as have been noticed under this short head lead to a study of another new point, namely, the possibility of the formation of organic alkaloids in the body during some conditions of disease. Scientific discovery has not, however, advanced so far as to enable me at this moment to do more than allude to one of the newest and most important studies in modern medical research."

Mechanism of Plant-Contraction.—Dr. J. Burdon-Sanderson, in a lecture before the Royal Institution of Great Britain, performed an experimental demonstration of the causes and phenomena of the excitability of plants. The number of plants which exhibit what is often called irritability is very considerable, but the illustrations of the lecture were drawn chiefly from typical specimens of only a few of the most familiar kinds, such as mimosa, dionea, and two or three others. The mimosa presents nearly the same appearance when asleep as when excited, but is then liable to a further change, by the operation of which it sinks to a still lower position and becomes limp. The excitatory effect is dependent on a vital change in the protoplasm of the cells, which may be observed when the plant is asleep as well as when it is awake. The cells of the plant, which unexcited are distended or charged with liquid, undergo on excitation a sudden diminution of tension or of expansion by the discharge of the water contained in them, which finds its way first into the intercellular air-spaces, and then out of the motor organ altogether. The discharge is due to a sudden loss of its water-absorbing power by the protoplasm of the cell, whereby the external cell-sac, whose elastic tendency to contract is kept in check only by the constantly distending action of the protoplasm presses upon it with force enough to squeeze out the cell-contents. This action being participated in by all the individual cells, the leaf-stalk, or whatever organ it may be that droops, necessarily becomes limp and falls. The motion of the leaf is, however "the result of the action of many hundred independent cells, all of which may act together, but may not. In either case they take a great deal longer to think about it; for during a period after excitation, which amounts at ordinary summer temperature to about a second, the leaf remains absolutely motionless." During this interval an electrical disturbance takes place in the plant, the character and operation of which were neatly shown by the aid of some extremely delicate apparatus. Obvious and well-marked differences were pointed out between the mechanism of plant motion and that of animal motion; but the differences are not essential, for they depend not on difference of quality between the fundamental chemical processes of plant and animal protoplasm, but merely on differences of rate or intensity. "Both in the plant and in the animal, work springs out of the chemical transformation of material, but in the plant the process is relatively so slow that it must necessarily store up energy, not in the form of chemical compounds capable of producing work by their disintegration, but in the mechanical tension of elastic membranes. The plant-cell uses its material continually in tightening springs which it has the power of letting off at any required moment by virtue of that wonderful property of excitability which we have been studying. Animal contractile protoplasm, and particularly that of muscle, does work only when required, and, in doing so, uses its material directly."

Origin of Winding River-Beds.—Major Stevanovics, a Hungarian officer, has published an essay on the laws by which the "wash" and meandering of rivers are regulated. Based on studies of the Theiss and the Danube, the principles he elucidates are illustrated in the windings of rivers the world over, with such variations only as differences in situations and exposures might occasion. The deviations which rivers are constantly making in their course are, it appears, determined by fixed laws, which engineers should be competent to find out and regard. To understand them more fully,