CH. X.] TETANUS. 127 



maximal, the two stimuli are added together, and though pro- 

 ducing a simple muscle curve, produce one which is bigger than 

 either would have produced separately. This is svmimation of 

 stimuli. 



Effect of More than Two Stimuli. 



Just as a second stimulus adds its curve to that written as the 

 result of the first, so a third stimulus superposes its effect on the 



Fig. 151. Curve of incomplete tetanus, obtained from the gastrocnemius of a frog, where 

 the shocks were sent in from an induction coil, about sixteen times a second, by the 

 interruption of the primary current by means of a vibrating spring, which dipped into 

 a cup of mercury, and broke the primary current at each vibration. (Tracing to be 

 read tight to left.) 



second ; a fourth on the third, and so on. Each successive incre- 

 ment is, however, smaller than the preceding, and at last the 

 muscle remains at a maximum contraction, till it begins to relax 

 from fatigue. 



Fig. 152. Carre of complete tetanus, from a series of very rapid shocks from a magnetic 

 interrupter. (Tracing to be read right to left.) 



A succession of stimuli may be sent into the nerve of a nerve- 

 muscle preparation by means of the Wagner's hammer of a coil, or 

 the vibrating reed previously mentioned (p. 117). This method 

 of stimulation is called faradisation. Figs. 151 and 152 show 



