364 STIMULATION OF NERVE AND MUSCLE. 



CHAPTER XXI. 



PRELIMINARY OBSERVATIONS ON THE STIMULATION 

 OF NERVE AND MUSCLE. 



I. Electrical Stimulation. Obs. I. Get ready a nerve- 

 muscle preparation and place the nerve on a pair of common 

 electrodes ; or simpty lay bare the sciatic nerve, slip the elec- 

 trodes underneath, and watch the leg for any movements indi- 

 cating muscular contractions. Connect the electrodes with a 

 battery of one, two, or three cells, a key intervening. Open 

 the key, and after a few seconds shut it again ; this is equiva- 

 lent to making and then breaking a current in the nerve. It 

 will be found that either at the breaking or at the making, or 

 at both making and breaking of the current, a single muscular 

 contraction is produced ; but that during the passage of the 

 current (provided the intensity be uniform) there is no con- 

 traction at all. 



Obs. II. Instead of a constant current, employ a single 

 induction shock. Each application of a single induction 

 shock (if strong enough), whether it be an opening shock or a 

 closing shock, will produce a single muscular contraction. 



Obs. III. Instead of a single induction shock, employ a 

 series of shocks rapidly following each other. These produce 

 a continued contraction, a tetanus, which lasts during the 

 whole time of the application of the currents, or until the 

 muscle is completely exhausted. For this purpose use the 

 apparatus of Du Bois Reymond. 



Obs. IV. Lay bare the gastrocnemius or any other muscle, 

 apply the electrodes directly to the muscle instead of to the 

 nerve, and repeat the above observations. The results will be 

 the same. 



II. Mechanical Stimulation. 06s. V. Pinch the nerve 

 sharply with a pair of forceps, prick the muscle with a needle ; 

 in either case a contraction will take place. 



III. Thermal Stimulation. Obs. VI. Touch lightly 

 either nerve or muscle with a hot needle ; a contraction will 

 follow. 



IV. Chemical Stimulation. 06s.. VII. Dip the end of 

 the nerve into a strong solution of common salt ; after a little 

 while a series of contractions running into tetanus will be ob- 

 served in the muscles supplied by the nerve. 



Obs. VIII. Kill the muscle and nerve by immersion for a 

 few minutes in water at 40. The above stimuli applied to 

 either muscle or nerve will produce no contraction. 



