550 A TEXTBOOK OF PHYSIOLOGY 



Owing to this property of summation, a number of success i\- 

 stimuli may cause a number of contractions between which the 

 muscle does not properly relax. The greater the frequency of the 

 stimuli, the less the relaxation between each contraction, until at last 

 a long, fused, compound curve is obtained, known as the " complete 

 tetanic curve." Tetanus is produced by about 30 to 50 stimuli 

 per second in the case of frog's striated muscle.' The number varies 

 with the temperature and the state of the muscle. When warmed, 

 more stimuli are required; when cooled, less are needed. If the 

 muscle be fatigued, fewer stimuli are required to induce the complete 

 tetanic contraction. 



FN;. 291. SAKTOIUUS OF FROG, STIMULATED ALTERNATLLY \vnu <A[.VANIC CURRENT 

 AND INDUCTION SHOCK AT THIRTY-SECOND INTERVALS. (<;. li. Mines.) 



Each' response to an induction shock is marked with a cross. At the beginning of 

 tracing the muscle was in NaCl 0-7 per cent. ; at arrow fluid was changed to 

 NaCl 0-65 per cent., KC1 0'05 per cent. 



The genesis of tetanus is studied by employing the vibrating reed. 

 By Varying the length of the reed, the number of stimuli per second 

 is easily regulated, and all forms of incomplete to complete tetanus 

 may be obtained (Fig. 2S7). Incomplete tetanus is sometimes termed 

 " clonus." Ankle clonus may be elicited in certain nervous conditions 

 when the foot is suddenly bent up. 



Powerful alternating currents, vibrating frequently to and fro 

 inapposite directions e.g., 1,000,000 per second may be passed 

 through muscle without producing excitation, and with suitable 

 apparatus, such a current may be sent through several people and 

 electric lamps. The former feel nothing, while the lamps glow. 



