CHAPTER VIII 



WORK OF MUSCLE J EXTENSIBILITY OF MUSCLE 



THE experiments to be performed on these subjects are recorded 

 upon a stationary drum which must be moved onwards for about 

 five millimeters by hand after each record. 



Make a muscle preparation, preferably the sartorius (see end of 

 chapter), place it on the myograph, and arrange that it shall be 

 stimulated, either directly or through its nerve, by induction shocks. 

 Arrange a mercury key in the primary circuit (which is not to include 

 the drum) and a short-circuit key in the secondary circuit. It is best 

 in these experiments to use tetanic stimuli furnished by the Neef's 

 hammer ; the Helmholtz modification should be employed (fig. 24). 

 The lever should have a light scale pan suspended from it ; such a scale 

 pan can readily be made from the lid of a pill-box. Determine : 



1. The effect upon the lift, the weight being constant (say about 

 thirty grams), of a gradual increase of the strength of the stimulus 

 from minimal to maximal. 



Note down on the curve the distances of the secondary coil at which the 

 results recorded are obtained. 



2. The amount of work which the muscle performs in lifting 

 different weights, the stimulus being constant and maximal and the 

 muscle free- weighted. Beginning with the weight of the scale pan 

 alone, weights are gradually added, and the muscle being stimulated, 

 an ordinate is described for each additional weight. The work of the 

 muscle is estimated as weight x height. 



Note down the weight which corresponds with each ordinate and the height 

 of the ordinate. The exact height to which the weight is raised is calculated 

 by dividing the height of each ordinate by the magnifying extent of the lever. 



Another result is yielded in this experiment ; viz. the effect of the gradually 

 increasing weights in producing extension of muscle in the resting and contracted 

 conditions respectively. For it is obvious that the lowermost point of any 

 ordinate described by the muscle represents the length to which the resting 



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