GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 125 



d. The height of the base-line after the tetanus shows the persistence of the 

 contracture condition. 



e. The height of the separate contractions followiug the period of tetanic 

 excitation was 22 mm., while the height of the first of the single contractions 

 preceding the tetani was 14 mm., which well illustrates how excitation may 

 increase irritability. 



/. The total height to which the curve was carried by the separate shocks 

 after the period of tetanic excitation exhibits the effect of the support offered 



Fir,. 57.— Effect of tetanizing excitations to increase the irritability of a muscle and at the same time 

 to produce a condition of contracture. The gastrocnemius muscle of a winter frog, connected with a 

 very light lever and a small weight, was arranged to write isotonic contractions on a Blowly moving 

 kymograph drum. The time was recorded in seconds at the bottom of the record, and above this tin- 

 movement of the interrupter of the induction apparatus was written by an electric signal. The muscle 

 was excited four times by breaking induction shucks at Intervals of two seconds; then it was subjected 

 to a tetanizing current, this being short-circuited for brief periods at intervals of two seconds; finally 

 it was again excited at two second intervals with breaking induction shucks of the same strength as 

 those used at the beginning of the experiment. 



by the contracture to increase the total height of contraction, and corroborates 

 von F rev's statement that supported single contractions may carry the curve 

 as high as tetanus. 



g. The rapid growth in the height of the crests of succeeding short tetani, 

 taken in connection with the lessening amount of relaxation during the inter- 

 val when the tetanizing current was shut off, and the curve of contraction 

 seen at the close of the tetani, all go to show how contracture may aid sum- 

 mation and staircase effects to give the great height to the tetanus curve. 

 Finally, it may be stated that the elasticity of the muscle gradually increases 

 as a result of tetanic excitations, and this may aid in the support of the weight 

 during long-continued tetanic contractions. 



7. Number <>f Excitations required to Tetanize. — The number of stimuli per 

 second required to tetanize a muscle depends largely on the nature of the 



