If we were to give a complete account of the psychology of rhythm, it would be impossible not to resort to a sociological and historical mode of treatment. By Dr. Wallaschek’s researches on primitive music it has been conclusively shown how important a part rhythm, as a means of facilitating co-operation, has played in the struggle for existence.[124] And this utilitarian explanation has recently been carried even farther by Professor Bücher, who points out the invaluable saving of effort which the individual obtains by regulating his movements in a fixed sequence of time.[125] We may think that Professor Bücher has stretched his point too far in endeavouring to derive almost all music and poetry from the economical exigencies of labour;[126] but there can be no doubt that in whichever way the ultimate origin of musical arts be explained, their development is largely due to the practical advantages of rhythm. These considerations, however, which will be developed in the following chapters, need not detain us here, where we have to do with the presumably non-utilitarian and purely æsthetic work of art. If the practical advantages of economy and co-operation can be eliminated,—if we can imagine a dance and a song which has not for its aim the facilitation or regulation of some form of work or the stimulation of some effort, which, in short, has its sole aim and purpose in itself,—then the art-element in this dance or song must be explicable without reference to “foreign” purposes. The only explanation we have been able to find is one which brings us back to the standpoint of the last chapter. Looking upon art as an essentially social activity, we naturally bestow our main attention upon rhythm as a factor of unification. But as we are not allowed to take into account its importance for _practical_ co-operation, we can only interpret it as a means of bringing about _emotional_ community. And it is evident that the fixed sequence in time, when used for the purpose of communicating a state of feeling, must produce the same effect as when it serves the purpose of diffusing and regulating the impulses to work. This fact can also be observed in all cases of social expression. The most general and simple states of emotional excitement, such as a festive mood or a warlike intoxication, may indeed be diffused with sufficient efficacy by simple contagious imitation. But even with regard to such eminently infectious feelings, if a great mass of men is to be collectively and simultaneously stimulated by a common execution of the appropriate expressive movements, these movements must be regulated by the adoption of a rhythm. On the other hand, as soon as the expression is fixed in rhythmical form its contagious power is incalculably increased. By its incessant and regular recurrence, the rhythm takes a ruthless hold of the attention, and thereby compels even the most recalcitrant to yield to the power of the transmitted feeling.[127]