The physiology of the circulation in plants, in the lower animals, and in man : being a course of lectures delivered at the Surgeons' Hall to the president, fellows, etc. of the Royal College of Surgeons of Edinburgh, in the summer of 1872 / by J. Bell Pettigrew.

  • Pettigrew, James Bell, 1834-1908.
Date:
1874
Catalogue details

Licence: Public Domain Mark

Credit: The physiology of the circulation in plants, in the lower animals, and in man : being a course of lectures delivered at the Surgeons' Hall to the president, fellows, etc. of the Royal College of Surgeons of Edinburgh, in the summer of 1872 / by J. Bell Pettigrew. Source: Wellcome Collection.

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    the arterial pressure is reduced; but if the divided nerve be stimulated by electricity, it is increased. (s.) If a portion of the base of a frog's heart be removed with a sharp knife or scissors, it acts rhythmically ; whereas a portion removed from the apex does not, as a rule, act rhyth- mically. This does not always hold true, but when it does, it is supposed to be due to an increase in the ganglia and nerves at the base of the heart as compared with the apex. (t.) If a ligature be adjusted so as to enclose or map off the sinus venosus of the frog's heart, it is found that when the ligature is tightened the sinus continues to pulsate, whereas the ventricle after a few beats is arrested in diastole. After a short interval the ventricle also begins to pulsate, but the pulsations of the sinus venosus and ventricle are no longer synchronous (Stannius). This experiment is supposed to prove that the sinus venosus contains an automatic nerve- centre, i. e. a ganglion in which nerve energy is accumulated and discharged at stated intervals or rhythmically. As, how- ever, the automatic motor centre has not been demonstrated to exist anatomically, the statement must be received with caution. Admitting, however, that the automatic motor centre really exists, the rhythm of the heart is still unex- plained. The mystery of the movement confronts us as before. The question, then, comes to be, What causes the automatic motor centre to act rhythmically? The answer to this question will probably bring us face to face with the hidden springs of life itself; and the why and the wherefore of existence, there is reason to believe, will for ever remain a sealed book. The theory of Irritability as bearing on the Action of the Heart, considered. — The voluntary muscles, according to Haller, are alone under the influence of the nerves ; the hollow muscles, such as the heart, stomach, bladder, and uterus, not being stimulated by their nerves but by their contents. In Haller's opinion, the blood is the stimulus to the heart. Dr. John Reid also adopted this view. He says, ' The ordinary and natural stimulus of the heart is the blood which is constantly flowing into its cavities. The greater irritability of the inner surface over the outer is evidently connected with the manner in which the stimulus is habitually Y 1