[20] Cleghorn, A.:  Am.  Journal of Physiol., 1898, I., p. 336.

While it is well recognized that a rhythm does not consist necessarily of sound sensations, the ‘rhythmization’ of a series of sound sensations in the ordinary perceived rhythms is a matter of great interest.  Ewald found strong reasons for believing that the ear is peculiarly connected with the motor apparatus.  The experiments of Hofbauer[21] and Cleghorn[22]show that any strong stimulus to either eye or ear modifies decidedly the reactions of cooerdinated muscles.  How shall we assume that the automatic movement cycle necessary to rhythmic perception is set up when one listens to a series of sounds?

   [21] Hofbauer:  Archiv f. d. ges.  Physiol. (Pflueger’s), 1897,
   Bd. 68, S. 553.

   [22] Cleghorn, A.:  op. cit.

It must be assumed that any chance sound sets up a contraction in a set of muscles, however large or small.  If but a single sound occurs, the phase of contraction in that muscle set is followed by a longer phase of relaxation, and the musculature is passive as before; it may be that the stretching of the antagonistic set of muscles weakly stimulates them, and they then contract during the relaxation phase and assist in restoring the original condition.

But if a second sound occurs toward the end of the relaxation phase, before the tension is quite exhausted, the movement will be repeated; the negative set of muscles will be more definitely stimulated, for the activity will not have been exhausted when the second sound occurs.  If the sound continues to recur at regular intervals, the movement cycle thus established will rapidly become cooerdinated.  The positive set in its vigorous contraction furnishes a limiting sensation which becomes a cue for its own relaxation and for the reciprocal contraction of the negative muscle set.  The contraction of the negative muscle set and the resulting changes in tension may become in turn a cue for the positive set.  The reaction is now of the circular type and the process has become self-regulative, though constantly reinforced by the recurring sound (which has become a part of the limiting sensation of the rhythmic movement cycle).

But it is very probable that the second sound may not be timed so as to come at the close of the relaxation phase in the set of muscles roused; moreover, in almost all rhythms there are secondary sounds occurring between the main beats.  What happens when a sound occurs out of place, early in the phase of relaxation, or just before or just after the climax in the contraction phase?  Does it make it impossible to establish the cooerdination, or destroy it if already established?