500 Dynamic Theory. 



where it is 0. The tension is negative all over the cross-sections, and is 

 greatest in the center of these, decreasing from these centers to the edges 

 where the cross-section meets the longitudinal section where it is l . 



When the shape of the piece of muscle operated with is different, the 

 tensions are differently distributed. In a rhombus the greatest positive 



FIG. 234. Diagram showing the principle 

 on which current circuits are formed in a reg- 

 ular muscle prism. The arrow heads show the 

 direction taken by the current. The tensions 

 are equal at each end of lines 6, 7 and 8, so 

 that there is no current in them. 



( Rosenthal.) 



n _^^^^ 



FIG. 234. 



tension is moved nearer the obtuse angle on the long side, and the neg- 

 ative nearer the acute angle on the end section. In the calf muscle the 

 tensions become more complicated. The large end is strongly positive 

 and the small end strongly negative. (See fig. 235.) The current of 

 greatest strength in this muscle is very strong. The action of oxidation 

 of muscle which takes place suddenly when the muscle is irritated, takes 

 place slowly when it is inactive, which accounts for the currents and 

 tensions always found in it. But if during the passage of a current 



FIG. 235. A Gastrocnemius or calf 

 muscle of the leg of a frog showing the 

 direction of the magnetic currents in 

 it when detached from the body. Its 

 irregular shape causes the tensions to 

 be different at almost all points. 



generated in the quiescent mus- 

 cle, the muscle is made to con- 

 tract, the current is weakened. 

 This indicates that the current 

 and the contraction have a common source of power, so that when one 

 form of movement is in activity there is less power for the other. When 

 the body is quiescent, the currents generated in the tissues on opposite 

 sides of the body, neutralize each other on account of its bilateral sym- 

 metry. But if one side is active, electricity is evolved in greater amount. 

 This was demonstrated by Du Bois-Ra3^mond, who .formed a circuit com- 

 posed of his body and a galvanometer, the wires leading from the gal- 

 vanometer terminating in two cups filled with salt water, in each of 

 which he inserted a forefinger, thus completing the circuit. A sudden 

 contraction of the muscles of the right hand and arm sent a current 

 away from that side toward the left. When the left side was contracted 

 the current was reversed. 



The muscles of all animals, so far as examined, when quiescent, gen- 



FiG. 235. 



1 The absolute potential is that of the earth ; but any point on the prism to which a 

 current can be made to How from other points is relatively 0. 



