THE PHENOMENA OF MUSCLE AND NERVE. 65 



stimulus with this arrangement a stronger current must be applied or the sec- 

 ondary coil pushed over the primary coil to a greater extent than with the other 

 arrangement. 



The Phenomena of a Simple Muscular Contraction. 



45. If the far end of the nerve of a muscle-nerve preparation (Figs. 

 11 and 13) be laid on electrodes connected with the secondary coil of an 

 induction-machine, the passage of a single induction-shock, which may be 

 taken as a convenient form of an almost momentary stimulus, will produce 

 no visible change in the nerve, but the muscle will give a twitch, a short, 

 sharp contraction, i. e., will for an instant shorten itself, becoming thicker 

 the while, and then return to its previous condition. If one end of the mus- 

 cle be attached to a lever, while the other is fixed, the lever will by its move- 

 ments indicate the extent and duration of the shortening. If the point of 

 the lever be brought to bear on some rapidly travelling surface, on which it 

 leaves a mark (being for this purpose armed with a pen and ink if the sur- 

 face be plain paper, or with a bristle or finely pointed piece of platinum foil 

 if the surface be smoked glass or paper), so long as the muscle remains at 

 rest the lever will describe an even line, which we may call the base line. 

 If, however, the muscle shortens the lever will rise above the base line and 

 thus describe some sort of curve above the base line. Now it is found that 

 when a single induction-shock is sent through the nerve the twitch which the 

 muscle gives causes the lever to describe some such curve as that shown in 

 Fig. 17 ; the lever (after a brief interval immediately succeeding the open- 

 ing or shutting the key, of which we shall speak presently) rises at first rap- 

 idly but afterward more slowly, showing that the muscle is correspondingly 

 shortening ; then ceases to rise, showing that the muscle is ceasing to grow 

 shorter ; then descends, showing that the muscle is lengthening again, and 

 finally, sooner or later, reaches and joins the base line, showing that the 

 muscle after the shortening has regained its previous natural growth. Such 

 a curve described by a muscle during a twitch or simple muscular contrac- 

 tion, caused by a single induction-shock or by any other stimulus producing 

 the same effect, is called a curve of a simple muscular contraction, or more 

 shortly, a " muscle-curve." It is obvious that the exact form of the curve 

 described by identical contractions of a muscle will depend on the rapidity 

 with which the recording surface is travelling. Thus if the surface be travel- 

 ling slowly the up-stroke corresponding to the shortening will be very abrupt 



FIG. 17. FIG. 18. 



A Muscle-curve from the Gastrocnemius of the Frog : This curve, like all succeeding ones, 

 unless otherwise indicated, is to be read from left to right that is to say, while the lever and 

 tuning-fork were stationary the recording surface was travelling from right to left. 



a indicates the moment at which the induction-shock is sent into the nerve, b the com- 

 mencement, c the maximum, and d the close of the contraction. 



Below the muscle-curve is the curve drawn by a tuning-fork making 100 double vibrations 

 a second, each complete curve representing therefore one-hundredth of a second. 



and the down stroke also very steep, as in Fig. 18, which is a curve from a 

 gastrocnemius muscle of a frog, taken with a slowly moving drum, the 



