PHYSIOLOGY OF THE NERVOUS SYSTEM. 



720r 



1. That there is invariably an accumulation 

 of vesicular matter around the points of im- 

 plantation of nerves in the centres, as already 

 referred to. This is true of all nerves in 

 the vertebrata and the higher invertebrata, 

 and we know of no reason to doubt it in the 

 lower invertebrata. 2. The quantity of the vesi- 

 cular matter around the point of implantation 

 of a nerve is in the direct ratio of its sire and 

 of the activity of its function. Under par- 

 ticular circumstances the quantity of vesicular 

 matter becomes so large as to cause a special 

 gangl ionic enlargement of the portion of the 

 centre in which the nerve or nerves may be 

 implanted. The cervical and lumbar enlarge- 

 ments of the spinal cord are due to this 

 cause: the gangliform swellings on the upper 

 part of the spinal cord in the gurnard (trivia 

 Lyra) are connected with the exalted func- 

 tions of the nerves of touch distributed to the 

 feelers, and contain a large quantity of vesi- 

 cular matter. A remarkable instance of the 

 developement of vesicular nervous matter under 

 similar circumstances is to be found in the 

 electric lobes of the Torpedo, in which are im- 

 planted the nerves distributed to the electrical 

 organ. These lobes are of very considerable 

 size, much exceeding that of any other part of 

 the brain, and they contain vesicular matter in 

 large quantity. The nerves implanted in them 

 are of great size.* 



Such facts as those cited in the preceding 

 paragraph denote clearly that the developement 

 of the nervous force is to a certain extent con- 

 nected with the vesicular nervous matter, and to 

 such a degree as to justify the opinion that this 

 element of the nervous centres may be viewed 

 as the dynamic matter, the originator of the 

 force. At the same time it must be borne in 

 mind that this form of nervous matter never 

 occurs alone, and that probably the union of 

 the two is necessary for the developement of 

 nervous power. Just as the union of two 

 metals in the galvanic battery is necessary for 

 the developement of the current, while one of 

 them, that, namely, which possesses the greatest 

 affinity for the fluid interposed between them, 

 seems to originate the current, and is on that 

 account called the generating plate, whilst the 

 other is called the conducting plate. 



Of the. nature of the nervous force. All 

 that we have said respecting the mode of deve- 

 lopement and the laws of the nervous force 

 denotes its polar character. 



We can no more detect by our senses any 

 physical change in the piece of soft iron which 

 is rendered magnetic by the galvanic current, 

 than we can discover a change in the particles 

 of a nerve stimulated to action by the same 

 current. That both the iron and the nervous 

 matter are thrown into an analogous state by 

 the same agent seems highly probable. In the 

 case of the iron the indication of the assump- 

 tion and of the maintenance of the polar state 

 is afforded by its power of attracting particles 

 of iron ; while in a muscular nerve the assump- 

 tion and maintenance of the polar state are 



* Savi, Etudes Anat. sur le Systeine Nerveux et 

 sur 1'Organe Electriquc dc la Torpillc. 



shown by the active contraction of certain mus- 

 cles, or a more tonic state of passive contrac- 

 tion. While the current is passing through a 

 motor nerve there is no active contraction of 

 the muscles; but that these organs are in a 

 more excited state than the ordinary one of 

 passive contraction seems evident enough, from 

 the readiness with which they assume a tetanic 

 condition upon the cessation of the passage 

 of an inverse current which had been allowed 

 to pass through their nerves for some time. 

 And the fact demonstrated by Marianini and 

 Matteucci, that the passage of a continuous 

 current through a nerve will after a time exhaust 

 its excitability, although not so quickly as a 

 current frequently interrupted, denotes that the 

 nerve is in an excited state during the actual 

 passage of the galvanic current. 



Is the nervous force electricity ? There is 

 so much resemblance, as regards their mode 

 of developement and propagation, between 

 the nervous force and electricity, that many 

 physiologists have been led to regard these 

 forces as identical. The nervous force, how- 

 ever, presents striking points of difference 

 from electricity, which render it highly impro- 

 bable that it is identical with that force, and 

 which show that if it be so it must be an 

 electricity of extremely low tension. 



1. The ordinary tests for electricity fail to 

 detect the existence of a galvanic current in the 

 nerves, whether during their quiescent or their 

 active state. The most delicate galvanometers 

 have been employed for this purpose, in vain, 

 by Prevost and Dumas, who were themselves 

 advocates of the electrical theory of nervous 

 action, by Person, by Miiller, by Matteucci, 

 and by myself. Person connected the wires of 

 a galvanometer with the surfaces of the spinal 

 cord in kittens and rabbits, in which spasmodic 

 action of the muscles had been excited by the 

 influence of nux vomica, and was unable to 

 discover any evidence of electrical action. It 

 had been affirmed that needles introduced into 

 the nerves or muscles of living animals became 

 magnetic during nervous and muscular action, 

 so as to attract iron filings, but neither Miiller 

 nor Matteucci has succeeded in obtaining such 

 a result from their experiments. Matteucci 

 took the precaution of employing astatic needles 

 for the purpose, but could detect no signs of 

 magnetization. He also introduced the pre- 

 pared limbs of a frog into the interior of a 

 spiral covered on its inside with varnish; the 

 extremities of this spiral were united to those 

 of another smaller spiral, into which he intro- 

 duced a wire of soft iron. The nerves of the 

 frog were irritated to excite muscular action, 

 and at the same time Matteucci sought to 

 ascertain if an induced current would traverse 

 the spirals and magnetize the wire, but to no 

 purpose. 



2. Were it to be admitted that the nervous 

 force and electricity were identical, it cannot 

 be doubted that the provision made for propa- 

 gating the latter force in the nerves is very 

 inadequate. The nerves are very imperfect 

 conductors of electricity; Matteucci assigns to 

 them a conducting power four times less than 

 that of muscle ; Weber slates that they are very 



