34 PHYSIOLOGY CHAP. 



contracture to the same height to which it rose above the abscissa 

 of the base line, previous to contracture (Fig. 25). Probably, 

 therefore, the rapid shortening of the muscle in contraction is 

 independent of the slow and persistent shortening in contracture. 

 The former depends on the activity of the anisotropous, the latter 

 on that of the isotropous substance. 



The fact that the tetanus-curve of a muscle rises normally 

 above the maximal twitch is, however, capable of a far more simple 

 interpretation. We have seen that the excitation spreads over 

 the muscle like a wave. Hence even after a maximal shock all parts 

 of the muscle cannot be simultaneously thrown into contraction. 

 On the contrary, the parts first excited already begin to relax before 

 the others reach the maximum of contraction (Fig. 16, p. 23). So 

 that with maximal shocks the extent of the muscular shortening 



FIG. 25. Two contractions of toad's gastrocnemius, before (1) and after (2) yeratrin contracture 

 (V) on exciting by maximal induction shocks. (Bottazzi.) 



depends on the point of excitation, the rate at which the contrac- 

 tion wave travels, and the rapidity with which the individual 

 portions of the muscle contract and relax. If, on the other hand, 

 a series of excitation-waves are sent in rapid succession through 

 the muscle, all its parts will finally be in maximal contraction at 

 the same time, which must obviously result in a much more 

 pronounced contraction (Fr. W. Frb'hlich). 



The general conclusion that can be deduced from this discussion 

 of the tone of the skeletal muscles is that tonicity may undergo 

 positive or negative oscillations, which are probably the expression 

 of corresponding changes in the elastic forces intrinsic to the 

 muscular protoplasm. These changes may be due to the tonic 

 influence exercised by the nerves on the muscles, or to stimuli 

 acting directly on the latter. After section or paralysis of the 

 nerves or motor end-plates the tone of the skeletal muscles is 

 abolished ; it is normal in healthy individuals in whom the 

 antagonist muscles exert reciprocal traction ; it becomes more or 

 less strongly exaggerated under certain special abnormal conditions 



