86 MUSCLE. 



strongest from the centre of the muscle toward the cut end, though 

 certain minor currents are developed with the electrodes in closer 

 proximity. The cut ends of a muscle are always electro-negative 

 to its equator. This phenomenon cannot be observed in uninjured 

 muscle when in the body, but any injury will render the injured 

 portion electro-negative to the rest of the muscle. This condition 

 ceases with the power of contraction, and cannot be demonstrated 

 in dead muscle. 



What is the effect of contraction upon this " current of rest " ? 



When the muscle is made to contract, the galvanometer needle, 

 which has indicated the passage of an electrical current during rest, 

 flies quickly back toward the zero indicating the cessation of the 

 current of rest. This action is known as the negative variation of 

 the galvanometer, and as soon as the contraction of the muscle has 

 ceased the instrument again indicates the presence of the current 

 of rest. 



What is the cause of these electrical currents ? 



This is not yet fully determined, but they are probably due to 

 chemical changes resulting from the physiological degeneration. It 

 has been held that such currents occur naturally in muscle as the 

 result of certain of the cells exciting electro-motive forces, but the 

 former theory seems the more plausible. 



What stimulus causes a muscle to contract? 



The stimulus is supplied by the motor nerve which is distributed 

 to the muscle.- 



How do the motor impulses reach the fibres? 



The nerve divides and subdivides in the muscle until only a 

 single axis-cylinder is supplied to a small group of muscle-fibres. 

 This axis-cylinder then forms a delicate plexus about the muscle- 

 fibres, and in the case of plain muscle-fibres ends in the nucleus of 

 the fibre. In the striped fibres there is a special termination in a 

 small granular mass called the motorial end-plate. 



Is the property of contraction inherent in the muscle itself, or 



does it depend upon the nerve? 

 It is a property of muscle. 



What artificial stimuli may be used to cause muscular contrac- 

 tion? 

 Certain stimuli may be applied to a muscle or to the nerve sup- 



