116 



PRACTICAL PHYSIOLOGY 



CHAPTER XII 



THE RELATION BETWEEN MUSCLE AND NERVE. 

 INDEPENDENT EXCITABILITY OF MUSCLE 



THE 



In addition to the experiments which have been described in the 

 elementary course (page 33), the following experiment upon the 

 sartorius muscle should be performed. 



The muscle is carefully dissected out and will 

 contract when its nerve, which passes into the 

 muscle at the middle of its inner border, is cut 

 across by the scissors. If the muscle be placed 

 between two glass-slides and examined under a 

 microscope, the distribution of its nerve can be 

 seen to resemble that shown in the diagram (Fig. 

 115). The finer branches of the nerves and even 

 the end-plates can be more readily seen if the 

 muscle be treated with acetic acid. There are no 

 nerves in the terminal portions of this muscle, 

 which consists of fibres running in a direction 

 parallel with its length. 



The sartorius muscle is dissected from the other 

 thigh and the nerveless parts are stimulated by a 

 pinch with a pair of forceps or by an electrical 

 shock the contract, the muscle possesses in- 



, . J .. , .,., 



dependent excitability. 



The absence of nerves from the terminal por- 



tions can also be shown in the following way. 



The muscle is suspended from its tibial end and 

 is lowered until the cut iliac end touches some strong glycerine 

 contained in a watch-glass ; it does not contract. A thin trans- 

 verse slice is cut away and the muscle is again lowered into 

 contact with the glycerine ; there is still no contraction. This 

 procedure is repeated until the nerves are cut across and on contact 

 with the glycerine are stimulated and make the muscle pass into a 

 contracted condition. 



FIG. 115. 

 Diagram of the 

 sartorius muscle 

 to show the dis- 

 tribution of its 

 nerves. 



CHAPTER XIII 



THE ELECTROMOTIVE PROPERTIES OF MUSCLE AND 



NERVE 



In uninjured and resting muscle and nerve there is no electric 

 current, but during activity a current, the " current of action" is 

 produced. Injury causes local activity around the damaged tissue, 

 and is therefore accompanied by an electric current, the so-called 

 " demarcation or injury -current." This electrical current produced 



