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APPENDIX 



D. Thermic. Apply gently very close to the muscle a large very hot 

 wire. It will contract. Gently apply the dried wire made very cold by 

 immersion in salted ice. It will perhaps contract again. 



E. Normal stimulation of muscle is a universal experience in our 

 bodies. 



Expt. 37. Analysis of the Contraction of Cross-striated Muscle 

 (Apparatus: Kymograph, etc., for graphic record of gastrocnemius' 

 contraction, altogether called a myograph, electro-magnetic signal, 

 tuning-fork.) Raise the drum off its friction-bearing. Place the signal 

 in the primary circuit and arrange it to write as closely as possible under 

 the muscle-lever. Have some one hold tuning-fork so as to write just 

 below or above the signal. Rotate the drum and so draw an abscissa 

 line. Pass maximal make induction-shocks (cutting out breaks) through 



FIG. 269 



Apparatus as set up by students to make a simple myogram. The drum, however, should 

 have been at the top of its spindle when the first curve was made. 



the muscle while drum is spinning at a rate that makes the contraction- 

 curve (myogram) four or five centimeters long. The height should be 

 about three centimeters. The signal registers the moment of the muscle's 

 stimulation, and the fork measures the elapsed time. Drop perpendic- 

 ulars (or arcs) from summit of contraction curve, and mark the begin- 

 ning and the end of the curve. Measure in hundred ths of a second (A) 

 the combined latent-period; (B) the period of contraction; and (C) the 

 period of relaxation. 



In analyzing the different parts of the myogram from a cross-striated 

 muscle one has to consider (1) the electrical latent period, (2) the mechani- 

 cal latent period, (3) the period of contraction, and (4) the period of relax- 

 ation. None of these are constant in muscles generally, even in the cross- 

 striated muscles of the same individual animal, for the various elements 

 vary according to many conditions in the muscle itself, with its shape, 



