A text-book of physiology, for medical students and physicians . ACTION. 47 compound contractions by voluntary stimulation of our has been pointed out that in very rapid contractions, such asoccur in the trilling movements of the fingers in playing thepiano, the duration of the separate contractions is so brief as tosuggest that they may be of the order of simple investigation of such movements by the older methodof recording with levers (von Kries) or by the newer method ofphotographing the electrical oscillations shows, on the contrary,that even the shortest po
A text-book of physiology, for medical students and physicians . ACTION. 47 compound contractions by voluntary stimulation of our has been pointed out that in very rapid contractions, such asoccur in the trilling movements of the fingers in playing thepiano, the duration of the separate contractions is so brief as tosuggest that they may be of the order of simple investigation of such movements by the older methodof recording with levers (von Kries) or by the newer method ofphotographing the electrical oscillations shows, on the contrary,that even the shortest possible voluntary contractions are brieftetani made up of a short lasting series of contractions fusedtogether. In all probability, therefore, our motor centers, when-ever they are stimulated by a so-called act of the will, dischargerhythmically a series of nerve impulses. As we shall see later,it is possible that certain of these centers, when stimulatedreflexly, may discharge a single nerve impulse and thus arousea simple muscular contraction (see Knee-kick).. Fig. 23.—Mossos ergograph: c is the carriage moving to and fro on runners by meansof the cord d, which passes from the carriage to a holder attached to the last two phalangesof the middle finger (the adjoining fingers are held in place by clamps); p, the writing pointof the carriage, c, which makes the record of its movements on the kymographion; w, theweight to be lifted. The Ergograph.—Voluntary contractions in man may be re-corded in a great many ways, but Mosso has devised a special in-strument for this purpose, known as the ergograph. It has beenmuch used in quantitative investigations upon muscular workand the conditions influencing it. The apparatus is shown anddescribed in Fig. 23. The person experimented upon makes aseries of short contractions of the flexor muscle of the middlefinger, thereby lifting a known weight to a definite heightwhich is recorded upon a drum. In a set of experiments the 48 THE PHYSIOL
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