424 



GENERAL PHYSIOLOGY 



one another so rapidly that between them there is no time for the 

 muscle to extend. In order to study the details of tetanic con- 

 traction, a myograph is employed (Fig. 206), the_ writing-lever of 

 which traces the movement of the muscle upon stimulation in^ the 

 form of a curve upon a revolving drum. If the muscle be stimu- 

 lated by means of a single, not too strong induction-shock, so 

 that it performs only a moderate contraction, a single curve is 

 obtained, the ascending limb of which represents the phase of 

 contraction, the descending limb the phase of expansion (Figs. 205, 

 //, and 207, I). But, if several induction-shocks be allowed 



Fig. 205.— /, Myograph. //, Curve of contraction. (After Helmlioltz.) ti, Moment of stimulation 

 by an induction-shock. 



to act upon the muscle in succession and at regular intervals 

 in such a manner that each succeeding stimulus reaches it at 

 the moment when it is just beginning to extend, the first 

 contractions are superposed, i.e., the shortening of the muscle 

 is continued with every succeeding contraction ; the shortening of 

 each contraction may be regarded as representing the resting 

 point of the muscle, and from this the shortening of the next 

 contraction rises. Thus, with every succeeding stimulus the curve 

 of shortening rises like steps and reaches a certain height, ai 

 which it is then maintained, still allowing the regular variations 



