ADVANCED EXPERIMENTAL PHYSIOLOGY 



81 



and its outlines can be made distinct by sponging it with the frog's 

 heart full of blood. 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 distribu- 

 tion of its nerve can be seen to resemble that shown 

 in the diagram (Fig. 77). 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 ; they 

 contract, the muscle possesses independent excitability. 



The absence of nerves from the terminal portions 

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

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

 cedure 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. 



Dia- 



gram of the sartorius 

 muscle to show the 

 distribution of its 

 nerves. 



CHAPTER XXL (Advanced). 



THE EFFECT OF A CONSTANT ELECTRICAL CURRENT UPON THE 

 EXCITABILITY AND CONDUCTIVITY OF NERVE. 



THE passage of a constant current produces changes in the excitability 

 of nerve, at the anode there is a condition known as anelectrotonus, 

 the excitability is diminished ; at the kathode there is an increase in 

 excitability, a state of katelectrotonus. The conductivity is also 

 affected, there is a fall in both the anodic and kathodic regions. 

 These effects can be shown by the following experiment, 



F 



