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MANUAL OF PHYSIOLOGY. 



transverse and longitudinal sections. Then the second (stimu- 

 lating) muscle is made to contract, the negative variation acts as 

 a stimulus to the nerves lying on it, and so the first (stimulated) 

 muscle contracts. Not only does this show the negative variation 

 of a single contraction, but it also demonstrates that the con- 

 tinued (tetanic) contraction produced by repeated stimulation is 

 associated with repeated negative variations. Because the con- 

 traction of the stimulated muscle whose nerve lies on the stimu- 

 lating muscle follows exactly all the variations of the stimulator, 

 and is kept contracted as long as the other is contracted, and, as 



FIG. 181. 



Diagram illustrating the arrangement in the Rheoscopic Frog A = stimulating limb. 

 B = stimulated limb. The current from the electrodes passes into nerve (N) of stimulat- 

 ing limb (A), causing its gastrocnemius to contract. Whereupon the negative variation 

 of the natural current between + and stimulates the nerve (N'), and excites the 

 muscles of B to action. 



we shall see presently, the continued contraction can only be 

 brought about by a rapidly repeated series of stimulations, so 

 that the electric condition of the stimulating muscle must undergo 

 a series of variations. 



If an isolated part of a muscle be stimulated, the contraction 

 passes from that point as a wave to the remainder of the muscle. 

 This contraction wave is preceded by a wave of negative varia- 

 tion, which passes along the muscle at the rate of 3 metres per 

 second (the same rate as the contraction wave, see under), lasting 

 at any one point .003 of a second, so that the negative variation 



