FUNCTIONS OF NERVOUS TISSUE. 357 



the existence of an Electric current, in a Nervous trunk that is actually engaged 

 in conveying motor influence, have completely failed, though made with the 

 greatest precaution. Thus, Prof. Matteucci having experimented upon the very 

 large crural nerve of a Horse, which was caused by stimulating its roots, to 

 throw the muscles of the leg into violent contraction, nevertheless found that, 

 although he used instruments of such delicacy as to be capable of detecting an 

 infinitesimally-small disturbance of the electric equilibrium, no such disturbance 

 was evident. 1 Further, it is well known that the conducting power of the 

 nerves is destroyed, not merely by dividing the trunk, but also by putting a liga- 

 ture round it ; which last operation does not diminish its powers as a conductor 

 of Electricty. Moreover, the various fibrils are not as completely insulated from 

 each other in regard to Electricity, as we know them to be with respect to nerv- 

 ous agency; for the first of these forces, when transmitted along a nervous trunk, 

 cannot be restricted to any fibre or fasciculus of fibres, but spreads through the 

 entire trunk, and even to the neighboring parts in which it is imbedded; whilst 

 the latter is continually restricted to a small portion of the trunk, as is mani- 

 fested by its results. Again, if a small piece of a nervous trunk be cut out, and 

 be replaced by an electric conductor, electricity will still pass along the nerve; 

 but no nervous force, excited by stimulus above the section, will be propagated 

 through the conductor to the parts below. And lastly, the conducting power 

 of Nerve for Electricity is stated by Matteucci to be not more than one-fourth 

 of that of Muscle ; whilst Messrs. Todd and Bowman give it as the result of their 

 experiments, that both Nerve and Muscle are infinitely worse conductors than 

 copper ; their power of conduction not ranking above that of water holding in 

 solution a small quantity of saline matter. 



365. We shall probably form the most correct idea of the relation which sub- 

 sists between Electricity and Nervous power, by regarding it as of the same kind 

 as that which subsists between Electricity and Heat or Magnetism. For as a 

 current of Electricity passed through a small wire generates Heat, and Heat ap- 

 plied to a particular combination of metals generates Electricity or as an 

 Electric current passed round a bar of iron renders it Magnetic, whilst con- 

 versely the Magnetic force will generate the Electric so do we find that a cur- 

 rent of Electricity, passed through a small portion of a motor or sensory nerve, 

 will excite the Nervous force in the remainder; whilst there seems reason, from 

 the phenomena of the Electric Fish, to consider that Nervous force may in its 

 turn generate Electricity. Hence we may regard them as closely correlated, 

 though not identical; 2 and this idea of ''correlation" we seem justified in ex- 

 tending to those other Physical agencies, which have been shown to be capable 

 of exciting Nervous force; namely, Heat, Light, Chemical Affinity, and Me- 

 chanical Motion. For there is adequate ground for the belief, that either of the 

 three former may be excited by Nervous agency, although its most obvious 

 manifestation is the production of movement; and that thus, as each of these 

 agencies is capable of developing Nerve-force, and of being in its turn developed 

 by it, their relationship to it is no less intimate than that which they bear to 

 each other, although a more special apparatus is required for its instrumental 

 operation. And considering that Nerve-force is the highest of all the mani- 

 festations of Vital power, alike in its general control over the bodily fabric, and 



1 See on this subject Prof. Matteucci' s various Memoirs in the " Philosophical Trans- 

 actions;" and his Lectures on the Physical Phenomena of Living Beings" (translated by 

 Dr. Pereira), p 259, Am. Ed. 



2 See Prof. Grove's Treatise "On the Correlation of the Physical Forces ;" and the Au- 

 thor's Memoir "On the Mutual Relations of the Vital and Physical Forces," in the "Phi- 

 losophical Transactions" for 1850. This doctrine has been formally adopted by Prof. 

 Matteucci, in his Eighth Series of "Electro-Physiological Researches," published in the 

 "Philosophical Transactions" for 1850, p. 296. 



