XL.] 



TWO SUCCESSIVE SHOCKS — TETANUS. 



221 



(6.) Arrange a nerve-muscle preparation as in fig. 119 to record 

 ^. on a slow-moving drum. Let the writing-lever be a short one. 

 ■ {(\) Fix the flat spring firmly in the clamp, with ten inches 



K projecting. Allow the drum to revolve, set the spring vibrating, 

 m and while it is doing so, open the key in the secondary circuit, and 

 before the spring ceases to vibrate short-circuit the secondary 

 current. 



(d.) Shorten the vibrating spring and repeat the experiment, 

 making the tracing follow the previous one. 



(e.) Make several more tracings on the same abscissa, and let 

 them follow each other at regular intervals, always shortening the 

 springs until the tracing no longer shows any undulations, i.e., 

 until it has passed from the phase of " incomplete " to " complete 

 tetanus." 



Fio. 144.— Tetanus Interrupter. W. Wood block ; VS. Vibrating spring; BS, BSF. Bind- 

 ing screws ; C. Movable clamp ; C. Clamp to fix spring ; M. Cup of Mercury. 



(/,) Take a tetanus-curve by introducing Neef's hammer (Helm- 

 holtz's side wire) instead of the vibrating flat spring. 



{(/.) Study the tracings. The first tracings are indented, but 

 gradually there is more and more fusion of the teeth, until a curve 

 unbroken by depressions is obtained. In the curve of complete 

 tetanus the ascent is at first steep, then slightly more gradual, 

 speedily reaching a maximum, when the lever practically records a 

 horizontal line parallel to the abscissa. When the current is shut 

 off the descent is very steep at first, and towards the end very 

 slow. 



3. Number of shocks required to produce tetanus depends on the animal, 

 the muscle, and the condition of the latter ; the more fatigued a muscle is, the 

 slower it contracts, and, therefore, the more readily does fusion of contractions 

 take place. A fresh fro 's gastrocnemius requires about 27-30 shocks per 



