GENERAL PHYSIOLOGY OF NERVE-TISSUE. 



119 



Intermediate contractions indicate nerve impulses of corresponding 

 intensity. 



Tetanization of a muscle indicates that the nerve impulses arrive 

 at the muscle with a frequency so great that the muscle does not 

 succeed in relaxing from the effect of one stimulus before the next 

 arrives. Incomplete as well as complete tetanus may be developed 

 by gradually increasing the frequency of the stimulus. The character 

 of the contraction caused by indirect stimulation i. e., though the 

 nerve does not differ in any essential respect from that due to direct 

 stimulation. 



ELECTRIC PHENOMENA OF NERVES. 



Electric Currents from Injured Nerves. It was discovered 

 by du Bois-Reymond that electric currents can be obtained from 

 nerves as well as from muscles, and 

 that the electric properties of the 

 former correspond in most respects to 

 those of the latter. The laws govern- 

 ing the development and mode of 

 action of the currents derived from 

 muscles are equally applicable to the 

 currents derived from nerves. 



A nerve-cylinder obtained by mak- 

 ing two transverse sections of any 

 given nerve presents, as in the case of 

 muscles, a natural and two artificial 

 transverse surfaces. A line drawn 

 around the cylinder at a point lying 

 midway between the two end surfaces 

 constitutes the equator. From such a 

 cylinder strong currents are obtained 

 when the natural longitudinal surface 

 and the transverse surface are con- 

 nected with the electrodes of the gal- 

 vanometer circuit. The strength of 

 the current thus obtained will diminish 

 or increase according as the electrode 

 on the longitudinal surface is removed 

 from or brought near to the equator. 

 If two symmetric points on the longi- 

 tudinal surface equidistant from the 

 equator are united, no current is obtainable. When asymmetric 

 points on the longitudinal surface are connected, weak currents are 

 obtained, in which case the point lying nearer the equator becomes 

 positive to the point more distant, which becomes negative. From 



FIG. 50. DIAGRAM TO ILLUS- 

 TRATE THE CURRENTS IN 

 NERVES. The arrowheads 

 indicate the direction; the 

 thickness of the lines indicates 

 the strength of the currents. 



