ELEMENTARY EXPERIMENTAL PHYSIOLOGY 37 



+ f 



f4 + V* 



FIG. 27. To show the stimulation of nerve or muscle under the skin at the 



cathode and at the anode on closing and on opening. 



(From Noel Baton's Essentials.) 



1. Extent of Contraction. 



With the hand in supination and the forearm semiflexed resting 

 on the table measure the length of the biceps. Now flex the forearm 

 to a small extent and measure the space through which the hand 

 has been lifted. 



From the elbow joint measure the length of the forearm and 

 hand to the finger-tips, and also to the insertion of the biceps. 

 Make a diagram, and from these data, and from your knowledge of 

 the mechanism of levers, calculate the extent to which the muscle 

 has shortened. 



Extent of contraction 



_ length of lever from fulcrum to power 

 length of lever from fulcrum to point 



height of lift of hand. 





2. Force of Contraction. 



Lift a weight of 2 kilograms in the hand, as in the previous experi- 

 ment, and calculate what weight directly applied to the biceps 

 muscle this represents. 



_ length of lever from fulcrum to weight 



~ length of lever from fulcrum to power X wei S ht lifted - 



This is a measure of the force of the particular contraction. 



Dynamometer. Study the dynamometer provided, and deter- 

 mine the force of contraction of the flexors of each hand. 



