MUSCLE 281 



branchets for thirty to forty muscle-fibres with reduced 

 velocity. Every particle of each fibre rises and falls ; but, 

 seeing that the wave of contraction is much longer than the 

 fibre, the whole fibre is in a state of contraction at the same time, 

 although not with equal vigour throughout its whole length. 



We cannot dismiss the further consideration of the electric 

 phenomena of nerves and muscles without some inquiry into 

 their meaning. It is evident that they are intimately related to 

 the molecular changes which constitute an impulse. But at 

 present the physics of the phenomena are beyond our grasp. 

 We may speak in a general way of dissociation of ions ; but we 

 do not really know what is happening at the spot which is in a 

 state of impulse. We cannot bring the transformation which 

 it is undergoing into line with chemical and physical trans- 

 formations which we understand. PfVbably the electrical 

 phenomena which mark it are not peculiar to muscle and nerve. 

 All living changes of state are of the same nature. Cellular 

 activity, or protoplasmic activity, to use a better term, 

 wherever it occurs, is accompanied by electrical change. But 

 it so happens that nerve-substance and muscle-substance have a 

 definite orientation which gives to the electric force a cumu- 

 lative effect. In a liver-cell it is dispersed in all directions. In 

 a muscle the change of potential at one particle is added to the 

 change at the next, until the sum of all these changes, trans- 

 mitted along the length of the fibre, is sufficiently large to deflect 

 the needle of a galvanometer. Owing to its summation it 

 attracts our attention. 



Although they cannot tell the true significance of the electro- 

 motive change which marks the passage of an impulse, 

 physiologists are in a much better position now than formerly 

 to controvert certain popular misconceptions. There is no 

 such thing as " nerve-force " in the vulgar sense. A nerve 

 does not transmit energy to a muscle. The muscle obtains the 

 energy which it dispenses when contracting from the foods with 

 which the blood supplies it. The nerve transmits an excita- 

 tion. Over-excitability is not a sign of strength, but of weak- 

 ness. Nor is an impulse in a nerve an electric current. It may 

 be generated by an electric shock, but a chemical stimulus 

 is equally as effective. The slow rate at which it travels, as 

 compared with electricity, puts it altogether out of comparison 



