156 ELEMENTARY BIOLOGY. [CHAP. 



N. The physiological properties of muscle and nerve. 



Place a frog under a beaker, with a drop or two of 

 chloroform : take it out immediately it becomes un- 

 conscious, which will probably be in a few seconds. 

 Now feel with a finger-nail for the depression beneath 

 the skin at the back of the animal's head, which in- 

 dicates the point of articulation of skull and spinal 

 column : it lies in a line joining the posterior borders 

 of the two tympanic membranes. Divide the skin 

 and muscles at this point until the neural canal is 

 laid open, and then pass a stout wire into the 

 cranium and down the neural canal of the vertebral 

 column. By this process (kn5wn as pithing) the frog 

 is rendered totally incapable of further consciousness, 

 though most of its tissues will retain their vitality for 

 some time. 



a. Remove the skin from one leg, so as to lay bare the 

 muscles : send an interrupted electric current through 

 any one of them (or tap the muscle sharply with the 

 back of a scalpel) : it will immediately contract, or 

 alter its form in a definite way ; it becomes shorter 

 and thicker, gaining in breadth just so much as it loses 

 in length; in so doing it moves the bones to which it 

 is attached. 



/>. Very carefully lay bare the sciatic nerve, taking care 

 not to crush or drag it : divide it as high up as pos- 

 sible, and, seizing it with a pair of forceps close to its 

 cut end, lay it over the electrodes of an induction- 

 coil. Probably when the nerve is cut the muscles of 

 the limb will contract: whether or not, they will 

 contract violently while the interrupted current is 

 going through the nerve. 



