THE EXCITATION OF NEKVE FIBEES 



269 



tion of the current cause slight apparent irregularities in the law of contrac- 

 tion as tested on man. 



In stimulating the nerves of man for the purpose of determining the conditions 

 of the different muscles, we may use either induced currents (generally called faradic 

 stimulation) or the make and break of a battery current (galvanic stimulation). The 

 electrodes are covered with chamois leather moist- 

 ened with salt solution in order to diminish the 

 resistance of the skin. When it is desired to 

 stimulate any given muscle the stimulating elec- 

 trode is brought as nearly as possible over the 

 spot where the muscle receives its motor nerve. 

 These ' motor points ' have been mapped out, 

 and reference is generally made to a diagram 

 in determining the point for any given muscle. 

 By reversing the current the stimulating elec- 

 trode may be made either anode or cathode. It 

 .is found that stimulation occurs most easily on 

 closure of the current when the stimulating 

 electrode is the cathode ; with the greatest diffi- 

 culty when the current is broken and the stimu- 

 lating electrode is the cathode. These different 

 contractions are generally represented by capital 

 letters, and the usual relationship is ex- 



pressed by the statement that CCC is obtained FlG - 



most easily, then ACC and AOC, and finally 

 COC. 



Electrodes applied to 



the skin over a nerve -trunk. In 

 A the polar area is anelectrotonic 

 and the peripolar catelectro- 

 tonic. The former condition 

 therefore preponderates, since 

 the current here is more con- 

 centrated. In B the conditions 

 are reversed, the polar zone 

 corresponding in this case to the 

 cathode. (WALLER.) 



CCC = cathodal closing contraction. 



ACC = anodal closing contraction. 



AOC = anodal opening contraction. 



COC = cathodal opening contraction. 

 When the motor nerve to a muscle has under- 

 gone degeneration the muscle also begins to de- 

 generate, and we find certain alterations in its response to artificial stimulation. 

 In the first place, the muscle may fail to respond to induction shocks, while it 

 may show an increased irritability for galvanic shocks. In the second place, qualita- 

 tive alterations in irritability may be present, so that ACC may be obtained with a 

 smaller current than CCC. These alterations are spoken of as the ' reaction of 

 degeneration.' 



