The relation which the pacer bears to the American Trotting Horse has for twenty-five years been a topic of much senseless discussion. In the historical sketch which served as an introduction to the first volume of the “American Trotting Register,” the attention of the breeding public was first called to this question, in a form that was somewhat tentative, and much less didactic than my judgment suggested, but it served as an introduction to the study of the question which it foreshadowed. From this initial paragraph grew the discussion that has been going on ever since, much of which has been the merest jargon. The essential oneness of the trot and the pace has been clearly demonstrated by thousands of experiences. The trotting inheritance that produces the fast trotter also produces the fast pacer; and the pacing inheritance that produces the fast pacer also produces the fast trotter. The trotting-bred John R. Gentry, with his pacing record of a mile in two minutes and one-half a second, is but a single instance of very many of the same character. The fastest harness racers in the world are the pacers, and it seems to make no difference whether the inheritance of speed comes from the trotter or the pacer. The subject of the pacer in his diversified historical relations to the American trotter will be found in different portions of this work, and all tending to show the significant fact that he is again rapidly attaining the position of honor among the equine race which he maintained for so many centuries in the far-distant past.