THEORIES OF CURRENTS IN MUSCLES AND NERVES. 659 



An alteration of the chemical processes in a part of the protoplasmic structure 

 may, according to Hering, have such an effect that the portion that is decom- 

 posed (dissimilated) is negative with respect to the unaltered portion, but also 

 that the portion that is replaced (assimilated) is positive to the remaining 

 portion. Hering thus distinguishes negative and positive alterations, which must 

 give rise to corresponding currents. 



According to Griinhagen and others the electrotonic currents are due to 

 internal polarization in the nerve-fibers between the conducting tissue of the 

 nerve and that of the sheath. Matteucci had already found that if a wire be 

 covered with a moist sheath and the latter be connected with the electrodes of 

 a constant circuit, currents due to polarization appear, resembling the electrotonic 

 currents in nerves. If either the wire or the moist covering be interrupted at a 

 given point, the polarization-currents do not pass beyond the point of discon- 

 tinuity. The polarization developed at the surface of the wire causes, through 

 its transitional resistance, the conducted current to pass far beyond the electrodes. 



Muscles and nerves consist in a similar manner of fibers surrounded by in- 

 different conductors. As soon as a constant current is closed on the surface, 

 internal polarization develops between the two, and this gives rise to the electro- 

 tonic diffusion of the current. The polarization disappears on opening the current. 

 It can be recognized from the fact that in the living nerve the galvanic resistance 

 transversely through the fibers is five times as great and in muscles seven times 

 as great as through their length. Recently also Boruttau states that all electrical 

 phenomena of the nerve can be explained if it be considered in its capacity as a 

 conductor. 



With reference to the currents developed during the activity of the muscles, 

 the currents of action, Bernstein established the doctrine that when a single wave 

 of irritation (contraction) passes longitudinally through muscle-fibers that are 

 connected at two points with the galvanometer, that point below which the wave 

 passes is negative with reference to the other. Occasionally local points of con- 

 traction are present in muscle-preparations in certain situations and these are 

 negative with relation to other resting points of the same muscle. In order to 

 explain the currents that appear in connection with tetanus of frog's muscles it 

 must be assumed that the extremity of the fibers takes part in lesser degree in 

 the process causing the negativity than the middle of the fibers. This is, 

 however, the case only in exhausted muscles or in those in process of dying. 



As will be pointed out on p. 663 the contraction occurring on direct application 

 of a constant current to the muscle takes place on closure of the current at the 

 kathode, on opening the current at the anode. It will, thus, be clear that with 

 the closing contraction the muscle exhibits negativity at the kathode, but with 

 the opening contraction at the anode. These facts according to Hering and 

 Biedermann explain the after-currents considered on p. 657. 



If a muscle is made to contract by stimulation of its nerve, the wave of ex- 

 citation passes from the point of entrance of the nerve in both directions and 

 it is likewise negative to the resting muscle. In accordance with the situation of 

 the entrance of the nerve into the muscle the ascending or the descending wave of 

 excitation will reach the extremity (origin or attachment) of the muscle earlier. 

 If, therefore, such a muscle be introduced by its upper and lower extremities 

 into the circuit of the galvanometer, that extremity will at first be negative that 

 is nearest the point of entrance of the nerve, for example in the gastrocnemius 

 the upper, and later the lower. There thus appear in rapid succession first a 

 descending, then an ascending current in the galvanometer-circuit, in the muscle 

 naturally in the reverse order. 



The same conditions are observed also in the forearm-muscles of man. If 

 these are thrown into contraction from the nerve, the point of entrance of the 

 nerve, 10 cm. below the elbow, is first negative, then the muscle-extremities if 

 the wave of contraction has reached these points with a velocity of from 10 to 

 13 meters in one second. In this experiment the brachial plexus is stimulated 

 in the axillary cavity. The conduction in the forearm (in the upper portion and 

 above the wrist-joint) is established by surrounding the skin with strips of 

 material saturated with zinc sulphate. The strips themselves come in contact 

 with the paper pads of the non-polarizable electrodes. 



If a wholly intact muscle free from current is made to contract entirely, no 

 current is set up either with the individual contraction or in the state of tetanus, 

 because at the same moment the entire muscular structure passes into a state of 

 irritation and into a firmer condition. With respect to the nerves also it has in 



