Electro-physiology and electro-therapeutics : showing the best methods for the medical uses of electricity / By Alfred C. Garratt.
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a direction from the centre towards the periphery ; " i. e., the large nerve trunks sometimes are annihilated, as from a central lesion, before the branching twigs ; and therefore, while the trunk of a nerve may have lost all excitability, still the fine ulti- mate nervous fibrils, that so minutely ramify the muscular tis- sue, may have as yet retained more or less of their susceptibility to an adequate stimulus. M. Claude Bernard,* of Paris, has re- cently removed a great objection to the Hallerian irritability, as is thought; for he shows that the motor nerves lose their excita- bility from the centre to the periphery only in case they have been previously separated from their nervous centre. When the sciatic nerve has been cut off from its connection with the spinal cord, severe galvanization of the trunk of that nerve will, after a given time, cause no more contractions in the muscles ; but if we now transfer the galvanizing to the branches of the nerve in the muscles, and near the periphery, some contractions will still be brought about. But if, on the contrary, the nerve had not been cut or otherwise severed, but had remained still in its nor- mal connection and physiological relation with the spinal cord, quite different phenomena are observed: the nerve now loses its properties in the inverse ratio ; i.e., from the periphery towards the centre. If the crural nerve of a frog is laid bare, and no more contractions are excited by galvanizing the nerve in or near the muscles, still are contractions produced, if the galva- nizing is done near the cord ; and if the whole nervous trunk has lost its excitability, contractions can even then be brought about by galvanizing the anterior root of the nerve near the spine. It is in this way that the nerves lose their excitability, if animals die cither from hemorrhage or from woorara. This can be illus- trated by taking a frog, and first cutting the lumbar nerves on the right side, then let the animal be poisoned by woorara. Now we shall observe that the nerves lose their excitability in the direction from the centre outward to the periphery on the right side, where the nerve was cut; but on the other side of the frog the nerves die in the direction from the periphery * Le<;ons sur la Physiologie, Paris, 1858, toI. i. p. 193. 15