CHAPTER XIII 



Experiments on the Electrical Conditions of Muscle 

 and Nerve 



A GALVANOMETER or electrometer is necessary to study these conditions, 

 but certain facts can be demonstrated without any special apparatus. 



Demarcation current of muscle : Contraction without metals. 

 By means of a glass rod, loop up the nerve of a nerve -muscle pre- 

 paration and allow its cut end to come in contact either with an 



injured part of the surface of its own 

 muscle (Fig. 51) or with other muscles. 

 There will be a contraction of its muscle 

 each time that the contact is made or 

 broken. The excitation is caused by 

 the passage through the nerve of part of 

 the demarcation current of the muscle. 



The result can sometimes be obtained 

 if the cut end of the nerve be allowed 

 to touch a part of the nerve nearer the 

 muscle : in this case it is the demarcation 

 current of the nerve which stimulates its 

 own fibres. 



This experiment is only likely to 

 succeed if a very excitable preparation, 

 obtained from a cooled frog (see footnote, p. 56), is 



FIG. 51. Experiment of the 

 contraction without metals. 

 gl, Bent glass rod ; n, nerve ; 

 m, muscle. 



such as is 

 employed. 



Action current of muscle ; Secondary contraction. Take a nerve- 

 muscle preparation, and lay its nerve over the muscles of another leg, 

 the nerve of which is placed upon electrodes (Fig. 52). Tetanise these 

 muscles ; the nerve of the first-named preparation will be stimulated 

 by the electrical variations which accompany the contraction of the 

 tetanised muscles. A nerve-muscle preparation thus used in place of 

 a galvanometer to indicate electrical variations is known as a rheoscopic 

 frog preparation. 



The result can also be obtained with single excitations. 



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