328 PRACTICAL PHYSIOLOGY 



current is allowed to flow in an ascending direction for ten minutes ; 

 breaking the circuit causes tetanus (Ritter's Tetanus). If the current 

 be reclosed the tetanus ceases (Fig. 206 (2)). After a further period of 

 ten minutes the current is again broken, tetanus occurs and will be 

 increased if the current be closed in the descending direction (Fig. 206 

 (2)). If the nerve be divided on the far side of the anode during the 

 tetanus, the twitches are not abolished for the excitation is occurring 

 at the former anode (Fig. 206 (2)). 



These results are more readily understood if it be remembered that 

 a rise in excitability occurs with the appearance of kalectrotonus and the 

 disappearance of aneledrotonus, and that a region of depressed excitability 

 is found in the part in which aneledrotonus is set up, or in which 

 kateledrotonus has just disappeared. A sudden rise in excitability pro- 

 duces a stimulation. 



CHAPTER XVI. 



THE EFFECT OF A CONSTANT ELECTRICAL CURRENT 

 UPON MUSCLE. 



IT has been already shown that the make and the break of a con- 

 stant electrical current stimulate nerve ; this is also the case with 

 muscle. On the make of the current the contraction starts from the kathode ; 

 at break the contraction starts from the anode. The appearance of 

 katelectrotonus and the disappearance of anelectrotonus stimulate 

 voluntary muscle ; for cardiac muscle this has already been proved 

 (page 50). 



The following experiments should be performed upon the sartorius 

 muscle. 



The Clamped Sartorius. A pair of unpolarisable electrodes are 

 made, and threads which have been well soaked in normal saline 

 solution, and covered with kaolin, are fixed to the kaolin plugs. The 

 sartorius muscle is carefully dissected from a curarised frog (page 49) ; 

 the muscle should not be cut away from its origin and attachment, 

 but pieces of the pelvic girdle and of the tibio-fibula are left, so that 

 ligatures may be tied to these without damage to the muscle. The 

 sartorius is now very carefully clamped in the middle by Gaskell's 

 clamp fastened to a vertical stand (Fig. 225, page 345) ; the muscle is 

 held, but not so tightly as to damage its continuity and power of con- 

 duction. The pieces of bone at the ends of the sartorius are fastened 

 by ligatures to two light levers fixed to the vertical stand, and then 



