138 



SPECIAL PHYSIOLOGY. 



Moreover, this tissue possesses within itself natural currents of elec- 

 tricity, which constitute what is called the muscular current; and, 

 lastly, this normal current is more or less disturbed during the period 

 of contraction of the muscle. Such currents are not peculiar to mus- 

 cle, but are most marked in this tissue. Indeed, in all live muscles, 

 when quiescent, in small portions of them, even in the minutest shreds 

 which can be operated upon, electrical currents are constantly passing 

 in certain definite directions. Their presence, their direction, and the 

 disturbances to which they are liable, are detected, and determined, 

 by means of extremely delicate galvanometers, constructed as just 

 described. 



For this purpose, it is not sufficient merely to place the pieces of muscle, or 

 other tissue, between the ends of the very fine galvanometer wire, but special 

 contrivances are needed to conduct the current from the soft tissue to the wire. 

 In two glass vessels, Diagram A, containing a solution of common salt, are 

 suspended by means of metal holders, m, supported on glass insulating rods, 

 (/, two pieces of platinum, p, which are connected respectively with the two 

 ends of the galvanometer wire, d, d. Little cushions of blotting-paper, 6, sup- 

 ported on small shelves in these vessels, but rising above their edge, also dip 

 into the solution of salt ; by absorption of some of the solution, they form two 

 moist surfaces of contact, placed at a short distance from each other, upon 

 which the piece of animal tissue experimented on can be laid, in any desired 

 position, by means of a thin holder of glass. If the two moist cushions be first 



Diagram A. 



Diagram A (Vierordt). Apparatus for detecting the existence, direction, and strength of the normal 

 electrical currents in animal tissues, p, one of the platinum plates, dipping into the solution of salt, con- 

 tained in one of the glass cells; m, metallic connecting rod, supported on the non-conducting glass rod, g, 

 and connected with the wire d, of the galvanometer. The same parts are seen on the other side, ft, indi- 

 cates two small cushions of blotting-paper which dip into the solution of salt; .<?. is another cushion moist- 

 ened with the same solution, which, when placed on the cushions b, completes the galvanometer circuit; 

 but no current passes, as there is no chemical action set up. If the cushion, s, be removed, and a piece of 

 living muscle or nerve be put in its place, instantly a current is formed, and the needle of the galvanome- 

 ter, n, s, moves to the right or to the left, and shows the direction and force of the current. 



connected by means of a third cushion, s, moistened with the same fluid, the 



tissue, Diagram B, then a portion of any currents, which may exist in the 

 tissue, is instantaneously conducted through the lateral moist cushions, the 

 saline solution, the platinum plates, and the wire of the galvanometer. The 

 needle immediately deviates to the left, 1, 2, or to the right, according to the 

 direction of the current ; and the relative amount of deviation in either direc- 

 tion, indicates the strength of the passing current, and the changes producible 

 in it. In such experiments, only a portion of the intrinsic currents of a tissue 

 is diverted through the galvanometer, so that the total strength of such cur- 



