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It was shown, in 1880, by Burdon-Sanderson and Page, that when the ventricle of the excised frog's heart is connected with a capillary electometer by two contacts, one lying on the base and other on the apex, then every contraction of the heart was associated with electromotive changes of the following type. The electrometer meniscus was displaced in a given direction, the displacement occurred in the opposite direction, which returned slowly; the recorded displacements are therefore of the type shown in fig. 1 of the annexed diagram. Most of these earlier experiments were carried out on the excised heart rendered motionless by a suitable ligature around the sino-auricular junction, and excited to activity by an induced current which was applied to the tissue, near one of the electrometer contacts. The observed effects were demonstrated to be due to the algebraic sum of an active process under one contact, of the propagation of this process to the tissue under the other contact, and of the occurrence of a similar active process at this further point. The two phases, such as occur in fig. 1, were further shown to be indicative of the time relations of these active processes. The electromotive change during the active process causes this tissue to become relatively negative as compared with the inactive tissue. This negativity commences under the proximal contact, nearest to the seat of excitation; its development is, however, cut short by a similar change occurring under the distal contact situated further off from the seat of excitation, thus giving the first electrometer displacement the character of a single spike. Whilst both changes are in full progress there is no electrical difference between the contacts, and thus an iso-electrical interval occurs; finally, the change outlasting the porximal one, a terminal displacement of opposite sign is produced. All these well-known results have been supposed, with little experimental warrant, to occur in the beating frog's heartin situ , and a discrepancy thus exists between the assumed electromotive phenomena of the beating frog's heart and the electrical changes actually observed in the beating heart of mammals and of man. Numerous records have been obtained in man and mammals by making use of Waller's discovery that the electrometer, when appropriately connected with the surface of the body, shows the electromotive changes which accompany each beat of the heartin situ . These have been supplemented by observations upon the exposed beating heart (Bayliss, Starling, etc.). The latest records of this type in the case of man are those which Einthoven has obtained by the use of his delicate string galvanometer. All these records differ fundamentally from the records obtained by Burdon-Sanderson with the excised heart of both the frog and the tortoise, for, although the effects are diphasic, the second phase in the mammalian heart is of the same sign as the first (as in fig. 2), instead of being of opposite sign. It has thus been suggested that there is a want of parallelism between the activities of the mammalian heart and those of the heart in the frog and the tortoise. The present experiments show that the changes observed when the frog's heart remainsin situ and supplied by blood are precisely similar to those known to occur in the mammalian heart, they also bring out a further new point of no little interest, since, under certain conditions, a return wave of activity proceeding from the apex to the base is clearly demonstrable; this wave succeeds that which proceeds from the apex. It is this return wave which is largely responsible for the extensive terminal phase of the whole electromotive effect in the beating heart.

Capillary electrometer records of the electrical changes during the natural beat of the frog's heart. (Preliminary communication.)