262 



MOTION AND COORDINATION 



out to the knee. Now cut 'out entirely the large muscle of the calf of 

 the leg (the gastrocnemius), but leave attached to it the nerve, the 

 lower tendon, and the bones of the knee. 

 Mount on an upright support, as shown in 

 Fig. 1 20, and fasten the tendon to a lever 

 below by a thread or small wire hook : 



i. Lay the nerve over the ends of the 

 wires from a small battery which are attached 

 to the support at A, and arrange a second 



FIG. 120. Apparatus break in the circuit at S. .At this place the 



for demonstrating proper- battery circuit is made and broken either by 



ties of muscles. a telegraph key or by simply touching and 



separating the wires. Note that the muscle 



gives a single contraction, or twitch, both when the current is made 

 and when it is broken. 



2. Remove the current and pinch the end of the nerve, noting the 

 result. With very fine wires, connect the battery directly to the ends 

 of the muscle. Stimulate by making and breaking the current as 

 before. In this experiment the muscle cells are stimulated by the 

 direct action of the current and not by the current acting on the nerve. 



3. With the wires attached to either the muscle or the nerve, make 

 and break the current in rapid succession. This causes the muscle to 

 enter into a second contraction before it has relaxed from the first, and 

 if the shocks follow in rapid succession, to continue in the contracted 

 state. This condition, which represents the method of contraction of 

 the muscles in the body, is called tetanus. 



NOTE. In these experiments a twitching of the muscle is frequently 

 observed when no stimulus is being applied. This is due to the drying 

 out of the nerve and is prevented by keeping it wet with a physiological 

 salt solution. (See footnote, page 38.) 



To show the Action of Levers. With a light but stiff wooden 

 bar, a spring balance, and a wedge-shaped fulcrum, show: 



1 . The position of the weight, the fulcrum, and the power in the 

 different classes of levers, and also the weight-arm and the power-arm 

 in each case. 



2. The direction moved by the power and the weight respectively 

 in the use of the different classes of levers. 



3. That when the power-arm and weight-arm are equal, the power 

 equals the weight and moves through the same distance. 



