CHAPTER XIII 



EXPERIMENTS ON THE ELECTRICAL CONDITIONS OF MUSCLE 



AND NERVE 



A galvanometer or electrometer is necessary to study these con- 

 ditions, 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 preparation, 

 and allow its cut end to come in contact 

 either with an injured part of the sur- 

 face of its own muscle (fig. 50) or with 

 other muscles. There will be a con- 

 traction 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 

 , . . ~ , , , Fio. 50. EXPERIMENT OF THE CON- 



demarcation current OI the muscle. TRACTION WITHOUT METALS, gl, 



BENT GLASS KOD ; n, NERVE ; 



The result can sometimes be obtained if m > MUSCLE. 



the cut end of the nerve be allowed to touch 



a part of the nerve nearer the muscle : in thib 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, 

 auch as is obtained from a cooled frog (see footnote, p. 53), 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. 51). 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 rkeoscopic 

 frog preparation. 



The result can also be obtained with single contractions. 



57 



