simultaneously throughout the length of the tube; but, commencing at one point, it continually propagates itself along fresh lengths of the tube, so that the contents are slowly driven forward. As a rule, such parts as are provided only with smooth muscle fibers are not voluntarily movable, while striated muscle fibers are subject to the will. The latter have, therefore, been also distinguished as voluntary, the former as involuntary muscles. The heart, however, exhibits an exception, for, though it is provided with striated muscle fibers, the will has no direct influence upon it, its motions being exerted and regulated independently of the will. Moreover, the muscle fibers of the heart are peculiar in that they are destitute of sarcolemma, the naked muscle fibers directly touching each other. This is so far interesting that direct irritations, if applied to some point of the heart, are transferred to all the other muscle fibers. In addition to this, the muscle fibers of the heart are branched, but such branched fibers occur also in other places; for example, in the tongue of the frog, where they are branched like a tree. Smooth muscle fibers being, therefore, not subject to the will, are caused to contract, either by local irritation, such as the pressure of the matter contained within the tubes, or by the nervous system. The contractions of striated muscle fibers are effected, in the natural course of organic life, only by the influence of the nerves.--ROSENTHAL. OVEREXERTION AND PERSONAL IMPRUDENCE (p. 40).--Among children there is little danger of overexertion. When a little child reaches the point of healthy fatigue, he usually collapses into rest and sleep. But with youth comes the spirit of ambition and emulation. A lad, for instance, is determined to win a race, to throw his opponent in a football scramble, to lift a heavier weight than his strength will warrant; or a girl is stimulated by the passion she may possess for piano playing, painting, dancing, or tennis. The moment of exhaustion comes, but the end is not accomplished, and the will goads on the weary muscles, perhaps to one supreme effort which terminates in a sharp and sudden illness, perhaps to days and weeks of continued and incessant application, during which the whole system is undermined. Thus is laid the foundation for a feeble and suffering maturity.