Report on the progress of human anatomy and physiology in the year 1844-5 / [Sir James Paget].

  • James Paget
Date:
1846
Catalogue details

Licence: Public Domain Mark

Credit: Report on the progress of human anatomy and physiology in the year 1844-5 / [Sir James Paget]. Source: Wellcome Collection.

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    true if the extent of surface in proportion to the volume of the brain be re¬ garded; for, according to M. Baillarger’s measurements, the human brain has less superficial extent in proportion to its volume than that of [tnanyj in¬ ferior mammalia. Physiology of particular classes of nerves. The Motor Nerves. It has been already mentioned that E. H. Weber has successfully employed the continuous electric current developed by a rotating magnet for maintaining constant contraction of the voluntary muscles. He has also* applied it for testing the functions of the pneumogastric nerves ; and it has been employed by Volkmann.t in an extensive series of experiments on the functions and modes of action of the motor nerves generally. The chief results are as follows : 1. The central organs, but not the nerves, are capable of an excitement which induces fixed muscular contraction even after the withdrawal of the external stimulus. For, with the magneto-electric stimulus applied directly to them or their nerves, the voluntary muscles, the oesophagus, separated fasciculi from the heart, and the iris (?) remain contracted just as long as the stimulus acts upon them, but no longer; but if the same stimulus be applied to the brain or spinal cord, the contraction of the voluntary muscles and oesophagus is prolonged after its withdrawal. 2. The motor nerves of the anterior, but not those of the posterior ex¬ tremities [of the frog], arise from the uppermost part of the spinal cord. For if the anterior part of the cord be electrified, the contraction of the anterior extremities is often prolonged after the withdrawal of the stimulus ; but that of the posterior extremities ceases with the cessation of the stimulus. Now, if the motor nerves of both extremities arose in the brain, this difference would be unaccountable ; and as, according to the preceding rule, it is stimulus of the central organs alone which induces prolonged contractions, it follows that the upper part of the cord is a centre to the brachial, but not to the sciatic, plexus [of the frog]. 3. The motor nerves of the heart, stomach, and intestines arise neither in the brain nor in the spinal cord; for none of these organs is thrown into fixed contraction when the brain and cord are directly stimulated by the magneto-electric current, although it is a law that all muscles will thus con¬ tract when either the origins or the trunks of their nerves are stimulated. 4. The heart has a central organ in itself. If, when cut out and whole, it is sufficiently excited by the magneto-electric current, it remains in fixed contraction after the current is interrupted ; a condition which never happens in muscles separated from their centres, or in separated portions of the heart itself; for in these the contraction ceases with the stimulus. 5. Central organs modify the motor stimuli passing through them, and are thereby regulators of movements, [the contractions hitherto mentioned are states of fixed cramp-like contraction ; the movements here named are move¬ ments of alternate contraction and relaxation]. For direct stimuli through the motor nerves always produce fixed contraction of their several muscles ; but if the same motor nerves be acted on by reflected stimuli, then (even though these stimuli be continuously applied to the incident nerve, as by the magneto-electric current) movements of the muscles ensue, and these with order and an appearance of purpose. The replacement of the cramp-like contractions by the orderly movements in such a case, can be accounted for only by the intervention of the central organ through which the stimulus acts upon the motor nerves. 6. The heart, stomach, and intestinal canal possess central organs, a por- * Archives de Physiologie, Janv. 184G. f Mailer’s Archiv, 1845, No. 5, p. 407.