222 



PRACTICAL PHYSIOLOGY. 



[XL. 



second to produce complete tetanus. The following table shows approximately 

 the number of shocks per second required to produce tetanus. 



If the muscle be fatigued, then more or less complete fusion takes place 

 with a smaller number of shocks per second. 



4. Take a tracing with 10 or 15 vibrations per second, and then test the 

 effect of different temperatures on the form of the tracing. Pour on the 

 muscle normal saline at the required temperature. Notice how cold helps 

 the fusion, while heat makes the tetanus less complete. 



5. If Ewald's coil be used (fig. 95) any number of shocks from i to 200 per 

 second can be obtained. 



ADDITIONAL EXERCISES. 



6. Interruption by a Metronome. — Instead of the vibrating rod or Neefa 



hammer, introduce into the primary 

 circuit a metronome (fig. 145), pro- 

 vided with a wire which dips into a 

 mercury cup introduced into the 

 primary circuit. Vary the rate of 

 vibration of the metronome, and ob- 

 serve the effect on the muscle-curve. 



7. Instead of using the spring held 

 in a clamp, a convenient form is sliown 

 in fig. 144. The spring is kept vibrat- 

 ing by an electro-magnet actuated by 

 two Grove cells. 



8. Magnetic Interrupting Tuning- 

 Fork. — Instead of a vibrating spring, 

 the primary current may be inter- 

 ru})ted by means of a tuning-fork of 

 known rate of vibration, and kept in 

 motion by means of an electro-magnet. 

 The instrument (fig. 146) is introduced 

 into the primary circuit, and every 

 time the style on one of the arms of the 

 tuning-fork dips into and comes out 



of the mercury placed in a small cup, the primary current is made and broken. 



Fio. 145.— Metronome. 



