THEORIES OF CURRENTS IN MUSCLES AND NERVES. 657 



in current, so that the former will have disappeared before the electrotonic in- 

 crease in current is observed; for the rapidity of the electrotonic alterations in 

 current is less than the propagation-velocity of the impulse in the nerve, 

 namely only from 8 to 10 meters a second. 



Upon the electrotonic process depends the secondary contraction from the 

 nerve. If the sciatic nerve of a frog-preparation be applied to a divided nerve and 

 then a constant current is sent through the free extremity of the latter (non- 

 electrical nerve-stimuli are ineffective) , contraction takes place in the frog-prepara- 

 tion. This occurs because the electrotonizing current in the excised nerve irritates 

 the adjacent nerve. On rapidly closing and opening the current secondary 

 tetanus results. The same conditions are observed in connection with the para- 

 doxical contraction. If the current is directed to one of the two branches into 

 which the severed sciatic nerve of the frog divides, the muscles supplied by both 

 nerves contract. 



If the constant current is opened, after-currents appear, which according to 

 du Bois-Reymond are due to internal polarization. In living nerve, muscle, and 

 electrical organ this internal polarization-current is always positive, that is it has 

 the same direction as the primary current, when a strong primary current of 

 short duration is employed. If the primary current be of greater duration, nega- 

 tive polarization eventually results. Between the two there is a stage in which 

 the preparation exhibits no polarization at all. Positive polarization appears par- 

 ticularly strong in the nerve when the primary current has the same direction as 

 the course of the impulse in the nerve, in the muscle when the primary current 

 passes from the point of entrance of the nerve to the extremity of the muscle. 

 An analogous condition is observed in the electrical organ. 



The muscle likewise exhibits the electrotonizing effect of the con- 

 stant polarizing current. A constant current in the same direction 

 intensifies the muscle-current, while a current in the opposite direc- 

 tion enfeebles the muscle-current. The effect is, however, relatively 

 feeble. 



THEORIES OF CURRENTS IN MUSCLES AND NERVES. 



In explanation of the currents in muscles and nerves du Bois-Reymond pro- 

 posed the so-called molecular theory. According to this, nerve-fibers and 

 muscle-fibers contain minute molecules, of electromotive activity, arranged suc- 

 cessively in series, and surrounded by a conducting indifferent fluid. The mole- 

 cules are in a peripolar electrical state, namely, provided with a positive equatorial 

 zone, directed toward the surface, and two' negative polar surfaces, facing the 

 transverse section. Each newly prepared transverse section exposes new negative 

 surfaces, and each artificial longitudinal section new positive areas. 



This arrangement explains the strong currents, for if the positive circuit be 

 connected by means of a closing arc with the negative transverse section, a current 

 must pass through this from the surface to the transverse section. On the other 

 hand, the theory does not explain the feeble currents. To comprehend these it 

 must be assumed that the electromotive activity of the molecules is enfeebled 

 with varying rapidity on the one hand at unequal distances from the equator, on 

 the other hand at unequal distances from the center of the transverse section. 

 Then naturally differences in electric potential will develop between the molecules 

 of greater activity and those that are already enfeebled. The muscles, however, 

 show that their natural transverse section, that is the extremity of the tendon, 

 does not become negative electrically, like an artificial section, but positive in 

 greater or lesser degree. In explanation of this anomalous phenomenon du Bois- 

 Reymond believes that a layer of electropositive muscular substance is still present 

 at the extremity of the tendon. To facilitate comprehension he considers the 

 peripolar elements of the muscle as consisting each of two bipolar elements, a 

 layer of the half-element being so applied to the extremity of the tendon that 

 its positive side is directed toward the free surface of the tendon. This layer 

 he designates the parelectronomic layer. It is never entirely wanting. The better 

 it is developed the greater is the absence of current on conduction from the sur- 

 face and the tendon. If parelectronomy be well developed, the extremity of the 

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