38 



PRACTICAL PHYSIOLOGY 



3. Work Done. 



From the extent of shortening of the muscle, and from the weight 

 lifted, calculate the work done by the biceps muscle. 



Work done = weight lifted X extent of contraction. 



Lesson VIII. To be provided for each pair of Students. 

 1.' A galvanic current from an accumulator or from a series of cells. A 

 resistance or rheocord. A commutator with crossed wires. Mercury key. 

 2. Wires with two flat zinc electrodes, one covered with chamois leather, 

 and two jelly cans containing saturated NaCl solution. Dynamometer. 



LESSON IX 

 The Course of Contraction of a Muscle 



METHOD. Make a frog's gastrocnemius muscle record its change 

 upon a moving surface. 



A. Apparatus. 



(1) Prepare an Induction Coil for single induction shocks, putting 

 the Drum, covered with smoked paper, in the primary circuit, so 

 that the two strikers below the drum make and break the circuit 

 as the drum revolves, and putting a short circuiting friction key 

 in the secondary circuit (Fig. 28). The direction of rotation may 

 be reversed by crossing the driving cord. 



(a) Always keep the key in the primary circuit open except when 

 using the current. 



(6) Always keep the key in the secondary circuit closed except 

 when stimulating. 



(c) Keep the driving cords clear of the switch-boards. 



FIG. 28. Arrangement for recording the Course of Contraction of Muscle, 



using switch-board instead of cells. 

 1. Induction Coil. 2. Drum. 3. Frog-board. 4. Mercury Key. 5. Friction Key. 



(2) With the key in the secondary circuit open, move the drum 

 with the hand in the direction in which it is driven by the string 

 so as to make and break the circuit and test the current passing 



