THE ELECTROMOTIVE PHENOMENA 289 



centre of the section, show a slight difference of 

 potential. 



Prove these several statements. 



Oblique Section. When the artificial cross- 

 section is oblique to the long axis of the muscle, 

 the maximum difference of potential is no longer 

 at the equator and the centre of the cross-section. 

 The most positive point is on the longitudinal 

 surface near the obtuse angle made by the oblique 

 section, and the most negative point is on the 

 cross-section near the acute angle. The structure 

 of certain muscles, the frog's gastrocnemius, for 

 example, is such as to make their natural cross- 

 section oblique. In consequence, their differ- 

 ences of potential are not distributed as in a 

 regular parallel-fibred muscle like the sartorius. 

 In the gastrocnemius, owing to the peculiar inser- 

 tion of the muscle fibres into the tendon, the 

 upper end of the muscle is really the middle of 

 the longitudinal section, while the lower end 

 is the acute angle of an oblique cross-section. 

 When the ends are connected with an electrom- 

 eter, a strong current is observed flowing (out- 

 side the muscle) from the upper to the lower end. 



Uninjured Muscle. Prepare a sartorius muscle 

 with extreme care to prevent injury. Connect 

 the tendon (the natural " cross-section " ) and 

 the longitudinal surface with the electrometer 



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