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A TEXTBOOK OF PHYSIOLOGY 



time tracing is simultaneously recorded on the drum. This may I;*" 

 done either with a tuning-fork or, better, with an electro-magnet 

 chronograph. 



When working with single induction shocks, the exact point at 

 which the stimulus is thrown into the muscle is obtained by placing 



FIG. 273. THE SIMPLE LEVER WITH AFTER-LOADING SCREW. 

 F, Clamp; L, lever; M, muscle. 



the kymograph in the primary circuit. The drum carries a metal 

 striker, which, as the drum revolves, strikes against a piece of metal 

 mounted on the stand of the drum but insulated from it. One 

 wire . is attached to the metal stand of the drum, the other to the 

 insulated metal. The current in the primary circuit is therefore 



FIG. 274. DIAGRAM OF THE APPARATUS FOR RECORDING. A SINGLE Musrn..u: 



CONTRACTION. 



rapidly made and broken when the striker hits and passes the 

 insulated metal (Fig. 274). 



In recording a muscle curve, the muscle may have a weight directly 

 pulling on it. The muscle is then said to be " loaded." If, however, 



