594 APPENDIX 



rapidly repeated stimuli. This sort of contraction is known as a 

 physiological tetanus or a tetanic contraction (p. 102). 



The Staircase Effect, Contracture, Fatigue. Prepare and 

 mount a gastrocnemius muscle as in the previous exercise. 

 Set the secondary of the inductorium at a position that 

 gives a sharp but not excessive break stimulus. With the drum 

 moving at its slowest speed make and break the primary circuit 

 twice per second, allowing the contractions to record themselves 

 on the slowly moving drum. Continue the series of stimuli until 

 the muscle ceases to respond. Make the record permanent. 



The increase in the height of the contractions during the first 

 part of the record, due to "warming up" is called the "staircase 

 effect." 



A rise in the base line during the later part of the curve is the 

 phenomenon of contracture (p. 100). 



The final failure of the muscle to contract is the result of fatigue. 

 This may be explained either as due to the exhaustion of the fuel 

 supply or to the accumulation of harmful "fatigue products." 



To distinguish between these alternatives replace the fatigued 

 muscle with a fresh one. Arrange the primary circuit for rapidly 

 repeated shocks of moderate intensity. With the muscle recording 

 on a slowly moving drum close the key, throwing the muscle into 

 tetanus. Continue the stimulation until the muscle is well fatigued. 

 Let the muscle rest for five minutes. Repeat the stimulation. 

 Recovery under this condition proves that the previous fatigue 

 could not have been due to exhaustion of the fuel supply. 



The production of acid in an active muscle may be demonstrated 

 with sensitive litmus paper. A resting isolated muscle is neutral or 

 slightly alkaline to litmus. The same muscle, exercised to fatigue, 

 is acid to litmus. 



The Influence of Temperature on Contraction. For thi 

 study arrangement must be made for immersing the muscle 

 in a liquid and at the same time recording its contractions. 

 A method of doing this is to mount an L-shaped glass rod in a clamp. 

 Fasten the femur end of the frog's gastrocnemius to the horizontal 

 end of the L. A small pulley must be mounted above the rod, 

 over which a thread can be led from the tendon of the muscle 

 the recording lever. Connect the ends of the muscle by fine cop 

 wire to the terminals of the secondary coil. Set this so that th 





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