720Q 



PHYSIOLOGY OF THE NERVOUS SYSTEM. 



inferior to the metals as conductors. And 

 from experiments made on this subject in 1845 

 by Dr. Miller, Mr. Bowman, and myself, we 

 were led to conclude that nerve was infinitely a 

 worse conductor than copper. The provision 

 for insulation, however perfect for the nervous 

 force, seems most insufficient for electricity, 

 unless, perhaps, for a current of very feeble 

 intensity. Yet we know that the nerve fibres 

 convey the mandates of the will with the nicest 

 precision to the muscles, and propagate the 

 effects of physical stimuli applied to the peri- 

 phery with the greatest exactness to the centre. 

 Tins could scarcely be if the force so propagated 

 were an imperfectly insulated electric current, 

 for it is evident that in such a bundle of fibres 

 as a nervous trunk disturbances would conti- 

 nually be taking place, from the secondary 

 currents induced in neighbouring fibres by the 

 electricity passing through those in action. 



3. The linn application of a ligature to a 

 nerve stops the propagation of the nervous 

 power along that nerve below the point of 

 application ; the passage of electricity, how- 

 ever, is not interrupted by these means. The 

 nervous trunk, indeed, is as good a conductor 

 of electricity after the application of the ligature 

 as before it, provided it do not become dry at 

 the point of ligature. 



4. If a small piece be cut out of the trunk 

 of a nerve, and its place supplied by an electric 

 conductor, electricity will still pass along the 

 nerve and along the conductor; but the nervous 

 force, excited by a stimulus applied above the 

 section, will not be propagated through the 

 conductor to the parts below. 



5. The existence of an organ in certain ani- 

 mals capable of generating electricity is un- 

 favourable to the electric nature of the nervous 

 force. The best examples of this organ are 

 found in the Torpedo and the Gymnotus; and 

 experiment has placed it beyond doubt that the 

 organ generates electricity, which is capable of 

 giving a shock similar to that from a Leyden 

 jar; which developes a spark during the dis- 

 charge, and can effect electrolysis; by which, 

 likewise, the galvanometer may be disturbed, 

 and needles rendered magnetic.* 



The electrical organs have no resemblance, 

 in point of structure, to nerves; they, however, 

 present a remarkable analogy in that respect, as 

 well as in their physiological action, to the 

 striped variety of muscles. They are composed 

 of a number of prisms, each of which consists 

 of a membrane closed at both extremities, and 

 containing a soft albuminous substance, but 

 subdivided by transverse very delicate septa 

 into a multitude of small compartments. The 

 bloodvessels and nerves are distributed upon 

 the enclosing membrane and upon the septa, 

 but do not penetrate the albuminous material. 

 On these septa, according to Savi, the nerves 

 form a network, in which the disposition of 

 their terminal fibres differs from that in muscle 

 in there being a true anastomosis or fusion of 

 the primitive tubules. The analogy of the struc- 

 ture of the electrical prisms with that of mus- 

 cular fibres is sufficiently obvious, the latter 



being prismatic columns of fibrine, enclosed by 

 a membrane, the sarcolemma, and separable 

 into discs, the nerves and vessels being distri- 

 buted upon the sarcolemma, and not penetrating 

 the contained sarcous elements. In both these 

 textures the anatomical disposition has evident 

 resemblance to the artificial arrangements for 

 generating electricity, and accordingly in one 

 (the electric organ) t; ue electricity is generated ; 

 in the other, as we shall see further on, either 

 electricity, or a force in close relation to elec- 

 tricity, is developed. In both cases the genera- 

 tion of the force is independent of the nervous 

 system ; its exercise and application, however, 

 are under the influence of that system. 



The arrangement of the nerves and nervous 

 centres is essentially different from that of 

 muscle or of the electric orgm, and so far 

 would suggest a decided difference in the cha- 

 racter of the force which they can developefrom 

 that produced by the latter textures. 



6. A comparison of the muscular with the 

 nervous force throws some light on the nature of 

 the latter, and upon its true relation to elec- 

 tricity. 



Matteucci has established beyond a shadow 

 of doubt that electricity of feeble tension is gene- 

 rated in the ordinary nutrition of the muscles 

 of all animals, and by a particular arrangement 

 this may be made to assume the current form, 

 passing from the interior to the exterior of the 

 muscle. The source of this electricity is no 

 doubt to be found in the chemical action which 

 accompanies the nutrition of the muscular 

 tissue, " principally that which takes place in 

 the contact of the arterial blood with the 

 muscular fibre."* The intensity of this cur- 

 rent increases in proportion to the activity of 

 muscular nutrition, and in proportion to the 

 rank the animals occupy in the scale of beings. 

 It requires a particular artificial arrangement to 

 accumulate the electricity in such a manner as 

 that it shall affect the galvanometer; "during 

 life the two electric states evolved in the mus- 

 cle neutralize each other at the same points 

 from which they are evolved ;" but in the 

 arrangement of a muscular pile as devised by 

 Matteucci, "a portion of this electricity is put 

 in circulation just as it would be in a pile com- 

 posed of acid and alkali, separated from each 

 other by a simply conducting body." 



During the active contraction of a muscle, 

 however, a force is developed which has re- 

 semblance to electricity, and in his early experi- 

 ments was regarded in that light by Matteucci. 

 This power is capable of affecting the nerve of 

 the frog in the same manner as electricity. The 

 following experiment displays this: Take the 

 lower extremity of a frog and skin it; dissect out 

 the sciatic nerve from among the muscles on 

 the posterior part of the thigh, and then sepa- 

 rate the thigh by cutting it across just above 

 the knee-joint, leaving the nerve connected 

 with the knee and leg; this preparation is the 

 galvanoscopicjrog, so called by Matteucci from 

 the readiness with which it indicates an elec- 

 tric current ; next prepare the lower extre- 

 mities of a frog according to Galvani's method : 



* Sec ELUCTRICITY, ANIMAL. 



Phil. Trans. 1845, p. 294. 



