Page:A Text-book of Animal Physiology.djvu/66

36 each other and the rest of the body; minor differences in the hands and feet, especially the greater freedom and power of apposition of the great-toe.

But the greatest distinction between man and even his closest allies among the apes is to be found in the development to an incomparably higher degree of his intellectual and moral nature, corresponding to the differences in weight and structure of the human brain, and associated with the use of spoken and written language; so that the experience of previous generations is not only registered in the organism (heredity), but in a form more quickly available (books, etc.).

The greatest structural difference between the races of men are referable to the cranium; but, since they all interbreed freely, they are to be considered varieties of one species.

The term rhythm to most minds suggests music, poetry, or dancing, in all of which it forms an essential part so simple, pronounced, and uncomplicated as to be recognized by all with ease.

The regular division of music into bars, the recurrence of chords of the same notes at certain intervals, of forte and piano, seem to be demanded by the very nature of the human mind. The same applies to poetry. Even a child that can not understand the language used, or an adult listening to recitations in an unknown tongue, enjoys the flow and recurrences of the sounds. Dancing has in all ages met a want in human organizations, which is partly supplied in quieter moods by the regularity of the steps in walking and similar simple movements.

But as rhythm runs through all the movements of animals, so is it also found in all literature and all art. Infinite variety wearies the mind, hence the fatigue felt by the sight-seer. Recurrence permits of repose, and gratifies an established taste or appetite. The mind delights in what it has once enjoyed, in repetition within limits. Repetition with variety is manifestly a condition of the growth and development of the mind. This seems to apply equally to the body, for every single function of each organism, however simple or complex it may be, exemplifies this law of periodicity. The heart's action is rhythmical (beats); the blood flows in intermitting gushes from the central pump; the to-and-fro movements of respiration are so regular