93 



Place in the scale pan, successively, different weights ; 10, 

 20, 30, 40, 50, 60, 70, 80, 90 and 100 or more. Put in the 10 

 gram weight. The lever will descend. Remove the weight 

 and the muscle will return to its original position. Replace 

 the weight, the lever will drop along the line it first made, 

 revolve the drum a very short distance horizontally and. add 

 10 grams more ; the lever will descend. Revolve the drum 

 again for a short distance equal to the previous horizontal 

 distance, add 10 grams more and repeat the above processes 

 until the heavy weights have been used. The " steps " of the 

 ' ' staircase " will become shorter and if the apices of all of the 

 "steps" be joined, the line will form a hyperbola. At the 

 end of the experiment remove the weights and note any con- 

 tractile phenomena. Does the muscle return to its original 

 position ? 



Repeat the experiment with a thin strip of rubber, substi- 

 tuted for the muscle. Join the apices of the "steps" with a 

 line and compare with. that of the preceding experiment. 



Test in the same way the elasticity of a short strip of 

 aorta (cat) provided for the experiment. 



Test also a short piece of the frog's intestine. 



332. Indbpendent Irritability of Musci<e. Appa- 

 ratus : Battery, induction coil,- two keys, wires, electrodes, 

 curare, etc. 



Arrange the battery and induction coil for an interrupted 

 current with one key in' the primary circuit and the other key 

 to short-circuit the secondary. 



Destroy the brain of a frog. Expose the sciatic nerve 

 and the accompanying artery and vein, on the left side, being 

 very careful not to injure the blood vessels. Isolate the sciatic 

 nerve and tie a stout ligature around all of the other struc- 

 tures of the leg. 



Inject 5 to 10 drops of the curare solution into the abdom- 

 inal cavity. The poison will be carried to every other part of 

 the body except the leg below the left ligature. The animal 

 is paralyzed in from twenty to thirty minutes. If the non- 

 poisoned left leg is pinched it is drawn up, showing that it 

 has not lost its reflex powers ; while the poisoned right leg 

 has lost its reflex. 



When the frog is thoroughly under the influence of the 



