LESSON IV. MAXIMAL CONTRACTION. 

 TETANUS. 



1. Relation of height of contraction to strength 

 of nerve stimulus. Arrange the apparatus for single 

 induction shocks. Make a sciatic -gastrocnemius pre- 

 paration and place it in the muscle chamber. It is best 

 to have the nerve and the points of the electrodes im- 

 mersed in the Ringer's fluid. Put on a 10 gram weight. 

 Place the secondary coil as far as possible from the 

 primary; make and break the primary circuit, pushing 

 the secondary coil slowly towards the primary until a 

 contraction is obtained. Then push back the secondary 

 coil 2 or 3 mm. at a time till the stimulus causes no 

 contraction. 



Arrange the lever to write on the drum, take off the 

 belt driving the drum and pull back the pulleys so that 

 the drum can be turned by hand. Turn the drum round 

 to mark a base line. 



Now stimulate with break shocks only (cp. Less. II, 

 5 b), pushing the secondary coil nearer the primary a 

 quarter of a centimetre at a time. When a contraction 

 is obtained (the minimal contraction) move the drum 

 about 5 millimetres between each stimulation. (The 

 drum may be moved a definite distance by marking the 

 pulley in equal sectors with chalk and turning it one 

 sector between each stimulation, the high gear being in.) 

 The contractions increase up to a certain point the 

 maximal contraction and then remain constant. 

 When the maximal contraction is obtained repeat the 

 stimuli, pushing the secondary coil a quarter of a centi- 

 metre at a time away from the primary. The heights of 



