CHAPTER IX 



FATIGUE OF MUSCLE AND NERVE 



Effects of fatigue on muscle : (a) On the form of the muscle curve.- 



Take a nerve-muscle preparation and fit it up as for recording the 

 simple muscle curve (p. 27). Make an abscissa, and mark, as usual, 

 upon it the point of stimulation. Take a normal curve with the 

 muscle free-weighted. Remove the writing point from the drum, 

 which is then allowed to revolve continuously and to stimulate the 

 muscle with each revolution. After fifty of such excitations without 

 record, apply the lever point again to the drum (making use, of course, 

 of the stop), and let the muscle describe another curve at the same 

 place as the first. Remove the writing point again for the duration 

 of fifty excitations, and repeat the above procedure, and so on a 

 number of times until the fatigue curves are pronounced. Notice 

 the effects of fatigue upon muscle, in prolonging the latency 

 period, diminishing the amount and slowing the course of its con- 

 traction, and greatly delaying, and at length even preventing, its 

 relaxation. 



A fatigue curve or series of curves can also be obtained by allowing the lever 

 point to remain in contact with the cylinder during the whole of the experiment, 

 and thus recording every contraction ; but the individual curves in a tracing so 

 obtained are very numerous, and tend to obscure one another. 



(&) On the extent of contraction. The effect of fatigue upon the 

 extent of contraction is best recorded upon a stationary drum, 

 moved by hand about half a millimeter after each excitation, or on a 

 very slowly moving drum ; the extent of the contraction is shown by 

 the ordinates described by the lever. Use the slowest rate of move- 

 ment of the drum (1 mm. per second or less), and arrange the primary 

 circuit so that it is made and broken about every half-second. This 

 can be done either by closing and opening a key by the hand, or 

 by allowing a metallic bridge, actuated mechanically (e.g. by a 



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