John Harvey Kellogg,
Plain Facts for Old and Young
“ Life Force.—To every thinking mind the question often recurs, What makes the fragrant flower so different from the dead soil from which it grows? the trilling bird, so vastly superior to the inert atmosphere in which it flies? What subtle power paints the rose, and tunes the merry songster's voice? To explain this mystery, philosophers of olden time supposed the existence of a certain peculiar force which is called life, or vital force, or vitality. ”
