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TEXT-BOOK OF PHYSIOLOGY 



galvanometer or capillary electrometer. When such electrodes are brought 

 in contact with a muscle properly prepared, there is at once developed and 

 conducted to the galvanometer an electric current the intensity and direction 

 of which are indicated by the deflection of the galvanometer needle. The 

 existence of this current is most conveniently demonstrated with single 

 muscles the fibers of which are parallel e.g., the sartorius, or the semimem- 

 branosus of the frog. If the tendinous ends of either of these muscles be 

 removed by a section made at right angles to the long axis, a muscle prism is 

 obtained which presents a natural longitudinal surface and two artificial 

 transverse surfaces. A line drawn around the surface of such a muscle 



prism at a point midway between the two 

 transverse sections constitutes the equator. 



When the natural longitudinal and arti- 

 ficial transverse surfaces are connected with 

 the wires of a galvanometer the terminals of 

 which are provided with non-polarizable elec- 

 trodes, an electric current is at once de- 

 veloped. In all instances the current, as 

 shown by the deflection of the needle, origi- 

 nates at the transverse surface, passes through 

 the muscle to the longitudinal surface, thence 

 through the galvanometer to the transverse 

 surface. The longitudinal surface is, there- 

 fore, electropositive, the transverse surface 

 electronegative. The two points exhibiting 

 the greatest difference of potential, and hence 

 the most powerful current, lie in the equator 

 and in the center of the [transverse surface. 

 Currents of gradually diminishing intensity 

 are obtained when the electrode placed on the 

 longitudinal surface is removed toward either 

 end. Feeble currents are developed when two 

 points situated at unequal distances, either on 



The arrowheads indicate the direc- corresponding or opposite sides of the equator, 

 tion; the thickness of the lines indi- are connected: in either case the current flows 



-^VS?X) eCUrrentS ' fr m the P int lyi nearest the equator to 



the point farthest from it. Similar currents 



are obtained when two points on the cross-section situated at unequal dis- 

 tances from the central axis are connected, in which case the direction of 

 the currents will be from the point lying nearest the periphery toward the 

 center. On the contrary, no current is developed when two points on the 

 longitudinal surface equally distant from the equator, or two points on the 

 transverse surface equally distant from the central axis, are connected. 

 Such points are said to-be isoelectric. These facts are shown in Fig. 34. 

 The natural ends of the muscle, enclosed by sarcolemma and tendon, do 

 not exhibit, if carefully preserved from injury, the negativity characteristic 

 of the artificial transverse ends. 



Similar electric conditions are exhibited by the muscles of man and other 

 mammals, by the muscles of birds, reptiles, amphibia, etc. The currents 

 developed by connecting the equator on the longitudinal surface with the 



