Nov. 8, 



NATURE 



43 



THE ORIGIN AND THE CAUSATION OF 

 VITAL MOVEMENT} 



11. 



'TTO this end i)erinit me to go a little into detail concerninti nerves. 

 -*■ Nerves arc processes of nerve- cells composed of fibrils 

 of immeasurable fineness, which, in the so-called axis cylinder of 

 the medullated nerves, are united by a stroma inside a very fine 

 membrane called the axolemma. In proportion to the micro- 

 scopic dimensions of the ganglion cells, of which the separate 

 nerve-fibres foim a part, these latter are for the most part enor- 

 mously long, many as long as orr arms and legs, and that is one 

 of the reasons why the perception of the unicellular nature of 

 the nerves made way but slowly. In fact, it was not easy to 

 accustom oneself amid the microscopic swarm of cells, to find 

 single ones so grown in length that they could he wound about 

 us like a cocoon thread. As it is the task and function of the 

 motor nerves to lead towards the periphery the impulses sent 

 out by their ganglion cells in the spinal cord, their activity 

 always admits of ready perception through the muscular twitch- 

 ing. Even when the nerve is divided and artificially excited at 

 the peripheral end, the muscles betray it. On the other hand, 

 no vi>ible physiological reaction is found at the central origin of 

 the motor fibre when stimulated at the periphery, so that at first 

 we were quite in darkness as to whether in general it conducted 

 ■-«>"tripetally. Nature, however, has presented us with a con- 

 mce by which we are enabled to demonstrate the possibility 

 uch an inverted or centripetal nerve-conduction. The con- 

 xance consists in the branching division of nerve-fibres, so 



Fig. 3. 



ently found in muscles, as will at once be seen in a pre- 

 lion from a frog (Fig. 3). In many muscles these branchings 

 arranged that we can use them for an experiment as 

 le as it is conclusive of nerve-conduction in both directions, 

 the gracilis muscle of the frog the nervation is fashioned 

 e manner displayed schematically upon this diagram 

 4), and-in more detail on the following (Fig. 5). In rea.lity 

 arrangemtnt is like this. Now, if 1 cut up the muscle 

 according to this diagram (Fig. 6), we get at the tip, z, nerve- 

 fibres, which are connected with the muscle-fibres at o and u 

 \\ by the branchings at the points x x, but which in life 

 . cd only for the parts of the muscle removed at/and/'. 

 \n experiment ^ will now convince you that nerves severed 

 ' fiom their own muscle-fibres act quite well backwards upon those 

 I placed centripetally to them, which they can only do if nerves can 

 , also conduct centripetally, and so long as a path is preserved for 

 - through the branchings. If we cut out the neighbourhood 

 he branchings, it is all over with the reaction of the muscle. 



' "On the Origin and <he Causation of Vital ^lovcmeat {L'eberiiie Ent- 

 stehvng der vitalen Bewegung)," being the Croonian Lecture del vered in 

 the Theatre ■ f the Royal Irsiitution on May 28. 18E8, by Dr. W. Kuhne, 

 Professor of Physiokgy in the University of Heidelberg. Continued from 

 »ol. xxxviii. p 629. 



* Kuhne, " Ueber das doppelsinnige Leitungsvermogen der Nerven." 

 2eitschr. /. Biol., vol. xxii. p. 305. 'Jo demonstrate the experiment on 

 tbczracilis. the muscle was fixed on a white piece cf cork by needles, and 

 held by elastic holders, and its image thrown on the wall highly magnified 

 by the so-called Kriiss lantern. 



We can make another experiment on the same muscle.^ We 

 see that when we excite the lower tip of the muscle, only the 

 lower portion twitches and not the upper. 1 he two portions are 

 in fact connected only by means of a very short tendon, the so- 

 called itnaiption, which passes completely through the muscle 

 {i i in Fig. 5), so that it really consists of two muscles. If the 

 nerve common to both is stimulated at any point, then both 

 parts of the muscle contract, but if the muscle substance itself is 

 stimulated, then the contraction travels no further from the place 

 where the stimulus was applied than to the limits of continuity of 

 the muscle- fibres. 



The power of motor nerves to conduct in both directions is 

 certainly of general significance in regard to the inner mechanism 

 of nerves, but we have only approached it here, because it was 

 necessary for the decisive proof of muscular irritability, as 

 obtained in our last experiment with the m. gracilis. Whenever 

 a muscle is provided with a nervation and branchings of the 

 separate nerve-fibres like that of the gracilis, some group of 

 muscle- fibres can serve to indicate whether a stimulus has 

 affected this alone or the nerves lying in it as well. If nerves 

 are present at the point of stimulation, and if the agent was at 

 the same time a nerve stimulus, this is shown by the simultaneous 

 contraction of distant parts which are accessible by means of the 

 nerve's power of conducting in both directions. In cases where we 

 can see the coarser nervation, the indirectly produced contractions 

 can be predicted, and these form so certain a criterion of neuro- 

 muscular excitations that by them the presence of the finest 

 nerves may be proved, whose existence might otherwise be quite 

 incapable of proof by any other means, as, for instance, by the 

 use of the microscope. If these contractions are wanting, as 



Fig. 5. 



was the case in our experiments with the lower end of the 

 muscle, we know that either the spot stimulated is free from 

 nerves, or that the stimulus employed was ineffectual as to the 

 nerves, and affected the muscle sub>tance exclusively. In both 

 cases, then, independent irritability is pioved for those muscle- 

 fibres which were directly excited and contracted. 



Now, since we have just employed an electric stimulus which 

 is equally effectual on muscle and nerve, it follows that we had 

 to do with the first case ; that is to say, the muscle showed itself 

 free from nerve at its end. We have reason for specially bring- 

 ing forward this experimental proof of the absence of any kind of 

 nerves in large tracts of muscle, because it compels those who in 

 spite of all assume the presence of nervous matter in certain 

 microscopic disks and strite of the muscle-fibre as a whole, to 

 deny that this supposed nervous element possesses any power of 

 conducting in both directions or any irritability at all ; for in fact 

 it is not possible to excite the motor nerve of a muscle-fibre by 

 any stimulus whatever applied to the actual terminations of the 

 nerve within the fibre. The facts besides combine to prove, as 

 need hardly be said, yet another proposition — they prove at the 

 same time that pure muscular excitation does not travel back to 

 the nerves. 



This maybe shown still better with the small pectoral muscles 

 of the frog's skin than with the m. gracilis. We need only dis- 

 sect it in the manner shown in the drawing (Fig. 7), and stimu- 



' Kiihne, ihiti., pp. 312, 324. 



