368 LAWS OF MUSCULAR CONTRACTION. 



But the variations will in most cases be due to the fact that 

 the nerve after stimulation, and the muscle after stimulation 

 and contraction, are for a variable period of time in a different 

 condition from what they were before. They are suffering 

 from more or less exhaustion, reaction, etc. To eliminate 

 these entirely is a task of considerable difficulty. They may 

 be more or less reduced by waiting a sufficiently long time 

 between each two trials, by working backwards from the 

 stronger shocks to the weaker, as well as from the weaker to 

 the stronger, etc. etc. 



The student, however, will see sufficient to enable him to 

 state that the amount of contraction does increase with the 

 increase of the strength of the shock (increase of stimulus) ^ 

 at first rapidly, then more and more slowly, and finally, when 

 the maximum is reached, ceasing to increase any more. 



III. The Contraction as a Function of the Resist- 

 ance. 



Obs. VI. Everything being arranged as in the last observa- 

 tion, place the secondary coil in such a position as to give a 

 shock about midway between the maximum and minimum 

 stimulus. 



First let there be no load to the muscle ; record the contrac- 

 tion as an ordinate on the abscissa line. Then load succes-- 

 sivcly with 10, 30, 50, 100, etc. etc., grammes; recording the 

 several contractions at proportionate distances along the ab- 

 scissa line. 



Repeat with a minimum stimulus and also with a maximum 

 stimulus. 



With (he same stimulus the amount of contraction decreases 

 as the load is increased; but not regularly. At first, as the 

 load is increased from zero upwards by small increments, the 

 contraction increases; as the load continues to be increased, 

 the increment diminishes, and finally gives place to a decre- 

 ment. The initial increase of contraction is most prominent 

 when the stimulus lies within a certain range of intensity. 



IV. The Work Done. 



06s. VII. The dimensions of the lever being known, deter- 

 mine from the ordinates of contraction the actual shortening 

 of the muscle itself during each contraction. This multiplied 

 into the weight will give the work done in each case. 



Draw an abscissa line and mark off from it distances propor- 

 tionate to the loads employed in Obs. VI. Draw as ordinates 

 the actual work done in the case of each load. A line drawn 

 through the summits of the ordinates will give the curve of 

 the work done with the same stimulus and increasing loads. 



With the same given stimulus and an increasing load, the 

 work done increases up to a maximum, and then declines. 



