muscle he has obtained a great series of marvelously beautiful records. Gotch and his pupils, using a similar arrangement, have been able to record the electrical changes in active nerves, even when stimulated by rapidly recurring shocks from an induction coil. It may surprise those who have not followed the progress of technique in the biological sciences to learn the extent to which photography is now applied in physiological research. Pictures of even such feeble vibrations as those which give rise to the sounds of the heart may be obtained by connecting a microphone placed near the chest and the primary coil of an induction machine in the same circuit, and photographing the movements of a capillary electrometer connected with the secondary. Exquisite photographs of the electrical variations occurring in the human heart at each beat, first demonstrated by Waller, have been recently published by Einthoven and Lint.
Loeb, working from another direction, has studied the effect of the ions contained in solutions of certain simple salts on rhythmical contraction in general, and particularly on the rhythmical contraction of the heart. He starts with the observation that a striped muscle in a solution of sodium chloride of a certain strength carries out rhythmical contractions which may last 24 to 48 hours. Salts of lime and of potassium hinder the contractions. Nevertheless the muscle remains longer alive when a small amount of calcium or potassium chloride is added to the sodium chloride solution. He explains the seeming paradox by the hypothesis that the sodium ions are the real stimulus for the rhythmical contractions, but yet exert on the muscle a poisonous influence, which, is counteracted by the calcium and potassium ions. He finds support for the idea that the sodium ions are actually poisonous to the living substance in the fact that Fundulus heteroclitus—a small marine fish with so marvelous a range of adaptation to its environment that it will live, on the one hand, in sea-water to which sodium chloride has been added to the amount of five per cent., and, on the other hand, in fresh and even in distilled water—-wall not live in pure sodium chloride solutions of about the same strength as sea-water, but will survive in sodium chloride solutions even twice as strong if a little chloride of calcium or of potassium be added. According to Lingle, one of the pupils of Loeb, sodium ions, while acting as the normal stimulus to the discharge ©f rhythmical contractions by the heart muscle of the turtle, exert upon it, in the absence of calcium and potassium ions, the same deleterious influence as upon striped muscle, a fact also demonstrated by Ringer and others for the heart of the frog. These are the experiments which that eminent contributor to the gayety of nations, the scientific newspaper reporter, has recently travestied under the caption, 'Discovery of the Elixir of Life in Chicago.' They have yielded fresh
