MUSCLE AND NERVE 65 



a hook. Place two non-polarizable electrodes against the opposite 

 borders of its upper portion. Make and break the current. When 

 made, the muscle deviates toward the cathode, and when broken, 

 toward the anode. 



Slit this muscle longitudinally to near its upper end. Place a piece 

 of rubber membrane between its two halves and adjust a non-polariz- 

 able electrode upon the surface of each. On the make, its cathodic 

 half will contract, and on the break, its anodic half. 



Isolate the opposite sartorius muscle with its attachments. Adjust 

 a screw clamp upon its central area and tighten it sufficiently so that 

 the wave of contraction is blocked without impairing the conduction 

 between its two ends. Suspend this preparation. Connect each end 

 of the muscle separately by means of a fine thread with a writing lever. 

 Adjust a non-polarizable electrode to each end. Make and break the 

 constant current. Note that the lever attached to the cathode moves 

 first on the make, whereas the lever attached to the anode rises first 

 on the break (Fig. 41). 



3. Law of Unipolar Stimulation of Human Muscle and Nerve. 

 Study the arrangement and, action of the apparatus, consisting of: 

 (a) 50 dry or moist cells connected in series, (6) a pole changer, and (c) 

 two clinical electrodes, one of which is broad and the other pointed. 

 The latter is equipped with a key, by means of which the current may 

 be made and broken. Moisten the felt lining of these electrodes with 

 saline solution, and apply the broad indifferent one to the shoulder. 

 The pointed stimulating electrode hold against the skin over the ulnar 

 nerve, near the internal condyle of the humerus. To begin with, 

 employ 8 cells, making and breaking the current while the anode is 

 over the nerve. Reverse the current, so that the cathode now lies 

 upon the nerve. Repeat the stimulations. Which stimulus is effective? 



Increase the strength of the stimulation by the addition of several 

 cells (possibly 4 to 6). Repeat the stimulations while first the anode 

 and then the cathode lies over the nerve. Which stimuli are effective? 

 Add other cells, and repeat the stimulations. Tabulate the results and 

 compare them with those forming the basis of Pflliger's law of polar 

 stimulation. State why the latter is not applicable to normal human 

 muscle and nerve* in situ f 



Annotation. Normal human muscle and nerve give the following results with 

 the constant current: 



We^k. Medium. Strong. 



ccc ccc ccc 



ACC ACC 



AOC AOC 



COC 



This shows that the cathodic closing stimulus is the strongest of all, and the cathodic 

 opening stimulus the weakest. Explain these results. 



