1825.] Scientific Noticed — Miscellaneous, 471 



agent in some of the most important phenomena of animal Ufe. 

 Their opinion, however, for a long time seemed to be supported 

 rather by analogy than by direct evidence. Comparatively but 

 a few months have elapsed, since two Swiss physiologists, 

 Prevost and Dumas, proved that muscular contractions in 

 whatever manner exerted, whethei: mechanically or chemically, 

 are invariably accompanied by a developement of electricity. 

 It still remained to be decided whether this electricity be 

 necessarily present as the essential cause, or merely as, an ac- 

 cidentally associated phenomenon. The following experiments 

 seem to carry us a step further towards the decision of the 

 question. 



Dr. Edwards has investigated the effects produced by touch- 

 ing a nerve in a manner which had been but little attended to. 

 It consists in passing a solid body along a nerve, in the same 

 manner in which we pass a magnet along a bar of steel which 

 we wish to magnetize; he conducts the experiment in the 

 following manner. He lays bare the sciatic nerves of a frog 

 in that part of their course in which they are situated on the 

 sacrum, leaving unimpaired their connection with the spinal 

 marrow, and with the muscles to which they are directed. 

 He removes the skin from the posterior extremities, that the 

 movements of the muscular fibres may be visible, and intercepts 

 vohtion by dividing the spinal marrow just below the head; 

 he then places under the nerves a slip of oiled silk, by which 

 they are raised and supported on a level with the bone. If a 

 metaUic rod be now drawn lightly along the denuded nerve, in 

 the mode above-mentioned, muscular contractions will be 

 excited. This effect is produced whatever be the metal em- 

 ployed. It is not even necessary that the rod should be me- 

 tallic. Horn, glass, ivory, or any other solid body will answer 

 the purpose, but their influence is by no means the same. 

 Though Dr. Edwards clearly ascertained this fact, continual 

 variations in the irritability of the animal precluded the pos- 

 sibihty of establishing a scale. The Doctor then substituted 

 for the oiled silk, which is a very complete non-conductor of elec- 

 tricity, a slip of muscle perfectly similar as to form and size, but 

 which, it will be remarked, is an excellent conductor. A re- 

 petition of the contact now no longer caused contractions, or 

 at most they were extremely feeble. 



In the first experiment, the electricity developed by the 

 contact of the nerve is retained, and its influence is concen- 

 trated on the nerve itself. In the second case, the electricity is 

 abstracted. If the presence of electricity were merely ad- 

 ventitious. Dr. Edwards thinks that the same mechanical 

 excitation ought in both cases to produce the same effect ; but 

 the difference is decided. He therefore concludes that elecj 

 tricity is essential to muscular contraction. 



