98 



or broken). The muscle lever will rise just after that of the 

 magnet. The tips of the two levers having started side by 

 side from the same vertical plane, the difference on the two 

 abscissas between the rising point of the lever from the mag- 

 net and the rising point of the muscle lever, will be the ap- 

 proximate latent period. Verticals drawn through the two 

 abscissas at the rising points of the two levers will be of use 

 in determining more accurately the extent of the latent period. 



Verify as far as possible on the tracing, the preceding 

 statements. Also obtain a curve from the make shock alone 

 (short circuit the secondary coil when the break shock should 

 occur). Vary the position of the secondary coil and compare 

 the curves. Get a tracing of the contraction of plain muscle, 

 by using a piece of the intestine or stomach of the frog. 

 Compare. 



341. Amplification or Magnification. The ampli- 

 tude of the tracing is measured by the ordinates ; it is the 

 distance which separates each point of the tracing from the 

 line of the abscissa. When the primitive length of the muscle 

 does not change as in the period of latent excitation, this dis- 

 tance equals 0, and the tracing is confounded with the line of 

 the abscissa : When the muscle shortens, the tracing is raised 

 above this line to a height relative to the degree of shortening. 

 When the muscle elongates the tracing falls below this line 

 to a certain extent. But as the muscle acts on a long lever, 

 the changes in the length of the muscle are amplified on the 

 tracing in a noticeable way. If, for example, the lever has a 

 total length of 150 millimeters and the tendon of the muscle 

 is attached to a point IS millimeters on the axis of rotation of 

 the lever ; each millimeter of muscle shortening will be pro- 

 duced on the tracing by a height (amplitude) of ten millime- 

 ters (1 centimeter). 



It is not difficult when one knows the length of the lever 

 and the distance from the point of attachment to the axis, to 

 calculate the actual degree of muscular shortening. 



Amplitude depends upon the length of muscular fiber ; 

 the longer the fibers of the muscle the longer the curve of 

 amplitude. In general the amplitude increases with the in- 

 tensity of the excitation, but there is a limit. 



Determine the amplitude in your tracing by measuring 



