MUSCLE 285 



physical laws apply. The protoplasmicity of protoplasm is 

 increased by warmth. What change of molecular constitution 

 does this imply ? 



The view that in a muscle molecular change gives rise to an 

 electrical change, which in turn produces the change in form, 

 has been very widely held. The hypothesis was based on 

 observations which seemed to show that the electric variation 

 travels a little ahead of the wave of contraction ; but every 

 improvement in recording apparatus has diminished this 

 apparent want of synchronism. There can be little doubt but 

 that the lagging behind of the wave of contraction is due 

 to the inertia of the muscle and of the recording apparatus. 

 Molecular change and electric variation are simultaneous. 

 If this be true, the electric change cannot be regarded as the 

 cause of the molecular change, in the sense, at any rate, in 

 which they used to be considered as cause and effect. 



The power of muscle varies as its cross-section. For human 

 muscles the maximum lift amounts to from 7 to 10 kilogrammes 

 for each square centimetre. This is a large figure, but it must 

 be remembered that, owing to the arrangement of the bones as 

 levers, most muscles act at a great mechanical disadvantage. 

 The greater the difference in distance from the fulcrum be- 

 tween the point of application of the force and the point of 

 incidence of the weight, when the force acts nearer to the 

 fulcrum than the weight, the greater is the mechanical dis- 

 advantage. The greater also is the rapidity with which the 

 weight is lifted. What is lost in strength is gained in swiftness. 

 Contrast the slow steps of a negro, whose long heel separates the 

 point of application of the power (tendo Achillis) from the 

 fulcrum (the ankle-joint), with the springy movements of a 

 European. A European needs, and as a rule has, a better 

 developed calf, which allows him his more sprightly gait, with- 

 out sacrificing his carrying power. Our preference for slender 

 wrists and ankles is not purely aesthetic, unless we admit, as 

 may be maintained, that all natural canons of taste rest upon 

 utility. Slimness of joints means nimbleness. A few muscles 

 act directly, without loss of power as, for example, the mas- 

 seter, which lifts the lower jaw (hence a grand capacity for 

 cracking nuts) but most muscles move levers of considerable 

 length. Compare with the masseter the biceps and brachialis 



