of a frog. Xote from time to time the condition of the frog. 

 What is the effect en reflexes and on general activity? 



\\ hen the animal is "veratrinized" remove the gastrocnemius 

 muscle plus sciatic ncn'c and mount in a moist chamber. To stimu- 

 late the nerve it is laid across "needle electrodes" in the moist 

 chamber; to stimulate the muscle, connections are made as usual 

 through the muscle. 



a. Record contractions when the muscle is stimulated by the 

 make or break of the induced current and a short tetanizing current. 



b. Record contractions when the ncrrc is stimulated by the 

 make or break of the induced current. 



Note character of curve. What part of the neuro-muscular 

 mechanism is affected by veratrin? 



201. Unipolar method of stimulation. To stimulate human 

 nerves a large "indifferent" electrode is placed over the skin where 

 there are no large nerves and a smaller "stimulating electrode" over 

 the nerve to be stimulated. Place the indifferent electrode, covered 

 with cotton soaked in physiological salt solution, over the biceps 

 muscle and connect with the indtictorium for single induced shocks. 

 Explore the inner surface of the forearm with the stimulating 

 electrode, also covered with salt-soaked cotton, and note the con- 

 tractions of the muscles of the fingers when their nerves are stimu- 

 lated. (See fig. in Howell, p. 93.) Draw an outline of the arm and 

 mark the "motor points" of four or five muscles which you have 

 been able to find on your arm. 



202. Record of human contractions Tlie er</o(/raph. Tie all 

 the fingers of the right hand except the index finger in the wooden 

 block of the ergograph and adjust the rod between index finger 

 and ergograph lever so as to record isotonic contractions of the 

 abductor indicis muscle. A celluloid writing point should be at- 

 tached by wax to the lever, or an aluminium point if the movement is 

 very slight. Take the following records : 



a. Unipolar single make or break induced shocks. The indif- 

 ferent electrode should be placed in the palm of the hand and the 

 nerve stimulated at the angle between first and second metacarpals. 

 Try also tetanizing shocks and record the contraction. 



b. Voluntary contraction, of a very short duration. Voluntary 

 contraction of several seconds duration. 



Then shift the rod toward the cast iron support of the spring 

 and take an isometric record of: 



c. Voluntary contraction of very short duration. 



57 



