IV. On the electromotive changes connected with the beat of the mammalian heart, and of the human heart in particular

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Abstract
In our investigation of the action of the excised Mammalian heart, Dr. Reid and I left undetermined certain points relating to its electromotive variations, more especially those which accompany the spontaneous heat of the excised organ, The nature and direction of deflections were very variable, and indicated no regular origin or mode of progression of the excitatory process. In 62 observations we observed in 17 cases apex negativity alone, in 17 base negativity alone, in 16 apex followed by base negativity, in 12 base followed by apex negativity. W e then remarked that the numerous irregularities met with in experiments upon the excised Mammalian heart were presumably due to irregularities and inequalities of tissue in the dying organ, which might have been due to differences of temperature, or to accidental injuries, &c.; but we were unable to verify the supposition by any experimental reproduction of these irregularities. Most of the observations reported in Part I. had for their object to clear this part of the subject as far as possible to me. 2. Experimental Modification of the Electrical Variation connected with the Spontaneous Beat. The methods followed have been in the main those described in the paper already referred to, with certain modifications of detail, such as the use of d’Arsonval’s chloride of silver electrodes (which proved to be convenient and excellent for the purpose in view), and with this difference, that, in order to examine the as far as possible intact and uninjured organ, the heart was examined in situ , the thorax being laid open and its walls fixed to a board immediately after the decapitation of the animal. The heart, having been examined in situ , was then excised and re-examined electrically.