LABORATORY MANUAL OF PHYSIOLOGY. 



III. INTERRUPTERS. 



For interrupting the primary circuit, any one of a number of de- 

 vices may be used. Where very rapid succession of shocks is de- 

 sired, as in the production of the so-called tetanizing current, the 

 Neef's hammer is used as shown in Fig. 6. Where known fre- 



FIG. 7. Tuning-fork Interrupter. (According to Kronecker.) i, Tuning fork; 

 2, electro-magnet, alternately made and broken ; 3, battery ; 4, mercury contact ; 5, 

 time marker. 



quency of interruption is necessary, a Bowditch clock or similar 

 arrangement may be used for low frequencies and metronomes and 

 electrically maintained tuning forks, for higher frequencies (see 

 Fig- 7)- 



IV. DISSECTION OF THE FROG'S THIGH AND LEG. 



With a preserved frog or a fresh one that has had brain and 

 cord destroyed, carefully dissect and identify the muscles of the 

 thigh and leg (see Fig. 8). 



1. Gastrocnemius-sciatic Preparation. Pith a frog. Re- 

 move the skin from one thigh. Make a circular incision through 

 the skin at the knee and another at the lower end of the leg. Slide 

 this up as far as the knee. This is to be slipped back, later, over 

 the muscle to keep it from drying. Separate the gastrocnemius 



[18] 



