CHAPTER VIII 

 Work of Muscle ; Extensibility of Muscle 



THE experiments to be performed on these subjects are recorded upon 

 a drum, which is moved onwards for about 5 millimetres by hand 

 after each record. 



Make a muscle preparation, preferably the sartor ius (see p. 22), 

 place it on a 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; 

 and preferable to employ the Helmholtz modification (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 

 30 grammes), of a gradual increase in 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 done 

 is calculated 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 muscle is extended by the particular 

 weight, and the top of the ordinate the length to which the muscle 



