176 ELECTRO-PHYSIOLOGY CHAP. 



and supported by a brass stirrup fixed to its upper end, which again 

 is attached to the brass holder of the tube. This stirrup is con- 

 tinued on the other side as a short, copper wire bent downwards 

 to dip into a steel cup filled with mercury (s). As the rod swings 

 to and fro, contact is made between the end of the wire and the 

 mercury. At the lower end of the pool is a terminal to which 

 the wire is fixed. When in use, the ebonite collar and bottom of 

 the glass tube are filled with salt clay, the upper part with solu- 

 tion of zinc sulphate, with the zinc rod dipping into it. After 

 the bone has been pushed through the orifice of the ebonite collar 

 into the clay, it is fixed by the screw. The bone at the other end 

 of the muscle is similarly fixed, so that the muscle is now 

 horizontally stretched between the two electrodes. Further, a 

 thread is attached to the lower part of each electrode, connecting- 

 it with a muscle pointer. Either of the electrodes can be fixed, 

 leaving the other to follow the shortening of the muscle." 



Assuming that the electrode of the pelvic bone is fixed, the 

 movement, or change of form, of the whole muscle can easily 

 be observed and graphically recorded, if the other free electrode 

 is connected with a long pointer (z), by a thread running- 

 horizon tally over two pulleys (R and r, Fig. 71) with a weight 

 at the end of it, the pointer again being attached to the axis of 

 the larger pulley. Since the writing-point naturally describes an 

 arc of a circle, the curve of contraction on the smoked surface is 

 more or less distorted, which, however, matters little in the present 

 consideration. If under these conditions the effect of varying 

 strengths of the constant current is investigated upon a curarised 

 (denervated) sartorius, it is easy to see that under the most 

 favourable conditions of excitability in the muscle, permanent 

 closure of a weak current never provokes more than a single 

 brief " twitch," which is at first insignificant in height, but 

 rapidly attains its maximal value, if the current increases in 

 intensity. 



Beyond a certain limit of intensity the height of the make 

 twitch remains constant ; other changes, however, appear in 

 the curve to which we shall refer later. On comparing the 

 maximal twitches produced by single induction shocks with the 

 maximal " make twitches " of the constant current under uniform 

 conditions, we are at once struck by the much greater height, as 

 well as the blunt, rounded top, of the latter. This can be 



