THE ELECTRICAL RESPONSE. 425 



that of tetanus produced by repeated stimulation, differ from this in certain 

 important particulars. Among these forms of continuous contraction 

 are (1) That which is evoked when a muscle is excited by the passage 

 of a constant current through its nerve ; (2) that caused by a single in- 

 stantaneous stimulation when a muscle has been poisoned by an extremely 

 small dose of veratrine ; and .(3) the reflex spasm of strychnine. 



To observe Case 1, it is best to use the muscle of a frog which has been 

 kept at a temperature approaching C. In such a preparation 1 it is easy to 



FIG. 239. Response to indirect excitation of a cooled muscle, injured at the 

 tendon end by plunging into hot salt solution, on closure of a constant 

 current (gastrocnemius). 



bring about a sufficiently persistent contraction, even with currents of moderate 

 strength. The form of the curve is seen in Fig. 239. It gives the same 

 evidence as before, that the muscle passes promptly into the excited state. 

 The curve exhibits undulations which occur with surprising regularity, the 

 significance of which cannot as yet be stated. A muscle which has been 



FIG. 240 Response to direct excitation of a veratrinised sartorius 

 devitalised at the tibial end. 



thoroughly veratrinised (Case 2), furnishes similar curves in response either 

 to direct or indirect stimulation, which, however, do not exhibit any undula- 

 tions (Fig. 240). For the observation of the strychnine spasm (Case 3), a 

 frog must be used which has received by injection into the lymph sac, an 

 extremely small dose of the drug. After exposing the muscle to be ob- 

 served, the leading-off electrodes are applied with as little interference with 

 1 Hering, "Biological Memoirs," Oxford, vol. i. p. 136. 



