64 PHYSIOLOGY OF MUSCLES AND NERVES. 



we called the stage of latent irritation. When, how- 

 ever, weights are placed on the scale of the apparatus 

 (fig. 20), the resulting deflections of the magnetic needle 

 are different, and are greater in proportion as the weight 

 applied is heavier. As the lever connected with the 

 muscle rests on, and is supported by, the plate below 

 it, the weights placed in the scale-plate cannot extend 

 the muscle ; they only increase the pressure of the 

 platinum point jp on the underlying platinum plate. 

 Before the muscle can contract after irritation, the ten- 

 dency to contraction must be greater than this pressure, 

 or than the tension which is exercised from below by 

 the weiofht on the lever. As the muscle strives to draw 

 up the lever, while the weight, on the other hand, draws 

 it downward, the greater force obtains the mastery. It 

 will be evident from what has been said that the muscle 

 acquires the force with which it strives to contract, not 

 suddenly, but very gradually. At the moment at which 

 this contracting force becomes slightly greater than the 

 weight applied, it is able to raise the lever, and in so 

 doing to interrupt the current which determines the 

 time. If, in a series of consecutive experiments, heavier 

 weights are each time placed in the scale of the appa- 

 ratus, and if the deflections of the magnetic needle re- 

 sulting from this are measured, this determines the 

 periods in which the muscle attains a tendency to con- 

 traction equivalent to the weight. We will call this 

 force the energy of the muscle. So long as the muscle 

 does not contract at all — that is, throughout the stage 

 of latent irritation — its energy = 0. From the periods 

 which we find as the result of the application of in- 

 creasing weights, it appears that this energy increases, 

 at first rapidly and then more slowly, reaching its maxi- 



