The experimental method in medical science : second course of the Cartwright Lectures of the Alumni Association, College of Physicians and Surgeons, New York delivered January 24, January 31, and February 7, 1882 / by John C. Dalton.

  • Dalton, John Call, 1825-1889.
Date:
1882
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Licence: Public Domain Mark

Credit: The experimental method in medical science : second course of the Cartwright Lectures of the Alumni Association, College of Physicians and Surgeons, New York delivered January 24, January 31, and February 7, 1882 / by John C. Dalton. Source: Wellcome Collection.

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    menters were busily occupied with galvanic electricity. They studied its action in a great variety of ways, and thus became acquainted with its mode of operation, and able to appreciate its phenomena. They found that when it was transmitted through any portion of a muscular nerve it produced contraction at the instant of closing the circuit; that afterward, while flowing through the nerve in a uniform current, it was without effect ; and that contraction again occurred when the current was discon- tinued. Even during the passage of the current, any sudden variation in its intensity, either of increase or diminution, would produce the same effect. It was the change in the electrical state of the parts, rather than their actual condition, which operated as a stimulus and provoked the contractions. The direction of the current, the length of nerve included within the circuit, and the frequency of making and breaking the connection, — all had a certain influence in the result. Experimenters found themselves provided with a new agent, by which they could investigate nervous action at their leisure, in ani- mals deprived of life, with the nerves and muscles ex- posed to view, and with far more delicacy and certainty than ever before; and the familiarity thus acquired with the operation of the galvanic stimulus prepared them for its more effective use in future investigations. The next event of sufficient consequence to form an epoch in the history of nervgus physiology was the dis- covery, in 1822, of the distinction of motor and sensitive properties in the two roots of the spinal nerves. Eleven years before, Sir Charles Bell1 had made some experi- ments on the spinal nerve roots of a recently killed rabbit, 1 Idea of a New Anatomy of the Brain ; submitted for the Observation of his Friends. By Charles Bell, F.R.S.E.