198 PHYSIOLOGY OF MUSCLES AND NERVES. 



between points in the cross-section respectively. The 

 position of these most strongly positive and most 

 strongly negative points depends on the angles which 

 the fibres form with the cross-sections, and may be 

 found by the rules given in the last paragraph as to the 

 influence of oblique section. 



Of all the many muscles of the animal body one 

 claims special attention, because, for purely practical 

 reasons, it is most frequently used in physiological ex- 

 periments : this is the calf-muscle (m. gastrocnemius). 

 It is easily prepared, even without severing its connec- 

 tion with its nerve, a fact which, for reasons presently 

 to be stated, is of great importance. It affords, as wc 

 shall see, a powerful current ; it long retains its capacity 

 for action ; and, in short, it has many advantages by 

 which we were induced, when studying the activity of 

 muscle and the excitabihty of nerves, to make use of it 

 almost exclusively. As, however, the structure of the 

 muscle is very complex, the nature of its electric action 

 is by no means easily understood. We must, however, 

 describe at least its main outlines, as we must employ 

 the muscle in further important experiments. 



In order to understand this action we must pre- 

 viously observe that it is not absolutely necessary to 

 cut a piece out of a muscle, but that entire muscles are 

 also capable of affording currents. In dealing with the 

 muscle-prism and muscle-rhombus, we assumed that 

 the pieces were cut from parallel-fibred muscles. The 

 longitudinal sections of these pieces retained their 

 covering of muscle-sheath (j^erimysium) and, in fact, 

 corresponded with the natural surface of the muscle. 

 The cross-cuts were, however, made into the actual 

 substance of the muscle, so that part of the interior 



