648 CURRENTS OF INJURY IN MUSCLE AND NERVE. 



The extremities of the horseshoe are surmounted by wooden spools (c d) , around 

 which an isolated wire is wrapped in numerous spirals. If the horseshoe is in a 

 position of rest, as indicated in the figure, it is exposed to the influence of the 

 large steel magnet, and it becomes magnetized itself. It turns to the poles of the 

 steel magnet the opposite poles s and n. In the wire of the two wooden spools 

 c and d an electrical current is developed whenever the horseshoe loses its mag- 

 netism or again acquires it. If half a rotation of the axis a b is made, so that 

 the spool c is apposed to the poles, the magnetism in the horseshoe naturally changes 

 its polarity, as the poles of the steel magnet N and S must always be in relation 

 to the opposite poles of the horseshoe. This alternation in the poles of the horse- 

 shoe can naturally be brought about only when the original magnetism present 

 disappears and the new magnetism of opposite polarity develops. The disappear- 

 ance of the magnetism in the horseshoe and the development of the opposite 

 kind gives rise in the spiral to currents in the same direction. With the second 

 half-rotation the poles are restored to their original position. There must, therefore, 

 be induced in the spiral a current of opposite direction from that of the current 

 resulting with the first half-rotation. Each complete rotation of the horseshoe 

 thus gives rise to two currents passing through the spiral in opposite directions, 

 so that the conducting wires o and p are alternately positive and negative. 



Stohrer has by the application of his commutator succeeded in causing the 

 two currents mentioned to pass in the same direction. For this purpose two 

 metallic collars (m and n) well insulated from each other are placed upon the 

 axis (a b) one over the other. Each collar is provided at both its upper and its 

 lower extremity with a hollow metallic half-ring: thus, the collar n with the half- 

 rings 3 and 4, and the collar m with the half-rings i and 2. The half-rings are 

 arranged alternately in pairs. Of the two polar wires of the spiral one (o) is 

 connected with the inner collar (m) and the other (p) with the outer collar (n). 

 The divided metallic plates Y and Z are prolongations of the poles and act as 

 conductors to the electrodes. It can be readily seen that in this position p passes 

 to 3 of the outer collar and thence to Z. After a half turn, however, o is con- 

 nected by 2 of the inner collar with Z. An analogous change in position takes 

 place at Y. If, now, as has already been pointed out, o and p change their polarity 

 with each half-turn, so that after every half-rotation first o and then p becomes 

 positive, by means of the commutator Z remains constantly connected with the 

 positive and, accordingly, Y constantly with the negative pole. The half-rings 

 i and 4, as well as 3 and 2, project somewhat beyond each other at their extremi- 

 ties. By this means it results that, in a certain position, o and p are closed for 

 a short time above and below by Z and Y. At this moment no current passes 

 through the electrodes. The apparatus is most efficient and it is also available 

 for electrolytic purposes. 



The key (Fig. 226, II) is an adjunct to this apparatus. It consists of a device 

 by means of which the current is made to pass through a wide metallic bridge 

 (y, r, z) until it is sent through the parts to be stimulated. The latter takes 

 place at the moment when the connecting metallic plate (r) is introduced between 

 the two blocks y and z. The key-electrode (III) can be employed in the same 

 manner for physiological purposes. This conveys the current to the tissues as 

 soon as the spring connecting plate (e) is raised by pressure upon k. This instru- 

 ment can be controlled with a single hand: a b are the polar wires, r r the insulated 

 electrodes connected with the parts to be stimulated, and G the handle of the in- 

 strument. 



ELECTRICAL CURRENTS IN RESTING MUSCLE AND NERVE. 

 CUTANEOUS CURRENTS. GLANDULAR CURRENTS. 



Method. To test the law governing the muscular current there is required 

 a muscle made up of parallel fibers and of simple structure, thus representing a 

 prism or a cylinder (Fig. 228, / and //). The sartorius muscle of the frog may 

 ibserve this purpose. In such a muscle a distinction is made between its surface 

 the natural longitudinal section, its tendinous extremities or the natural trans- 

 verse sections, and, if the latter are divided at right angles to the longitudinal 

 xis.the artificial transverse sections; finally the designation equator (a b m n) is 

 applied to an imaginary line that exactly bisects the length of the muscle-fibers. 

 As the currents present are'exceedingly feeble, a multiplicator (Fig. 225, I) is 



