SEVENTEEN FIGURESEt du sensim emoritur cor, videre licet, post duas vel tres pulsationes auricularum, aliquando quasi espergefactum cop respondere, et unum pulsum lente, et aegre peragere et moliri.WILLIAM HARVEY, "De Motu Cordis."One finds it pleasant to recall that the recognition of disturbance in the sequence of contraction in the chambers of the mammalian heart came with the damn of experimental cardiac physiology and the immortal u7ork of its first master. The earliest operations designed to produce artificially auriculoventricular dissociation were unfortunately of a character involving such widespread damage to heart muscle that little information could be gleaned from the varied disturbances of function which resulted. In 1894, the year following his description of the auriculoventricular bundle, William His, Jr.(27 to 29), attempted to destroy the connection between auricle and ventricle in the heart of the rabbit. In preliminary reports he described an experiment in which dissociation of the auricular and ventricular rhythms was produced.He mentioned the illustration of his results by means of a curve, but neither graphic records nor histological evidence have subsequently been submitted. Further work upon various animals, extending over the first decade of the present century, carried out by Humblet(30, 31), Hering(22 to 26),