572 



NATURE 



[April i6, 1908 



the simple reflex we are considering. The coordination 

 goes much farther than we have yet assumed. The 

 musculature of the limb is an instance of that kind of 

 musculature which obtains where parts are adapted to 

 move, not in one direction only or one way only, but in 

 many. The limb has to do many different things. It has, 

 according to circumstances, to bend or to straighten, to 

 turn inwards at one time, at another to turn outwards, 

 to move this finger or move that. Its musculature is 

 therefore split up into many different muscles — some doing 

 this, some doing that. Hence it comes that in the limb 

 are muscles which when they contract do with the limb 

 exactly opposite things. Thus wo find a set of muscles 

 which bend the knee, and another which straighten the 

 knee ; so, similarly, at hip and ankle, at elbow, shoulder, 

 and wrist. These muscles of opposed action are 

 called antagonists. Now in the flexion reflex — thi; reflex 

 we are considering — when the reflex bends the knee by 

 causing the flexor muscles to contract, what happens with 

 regard to the muscles which straighten the knee? Do 

 the opponents, the muscles which straighten the knee, con- 

 tract, or does the reflex nervous influence leave these 

 muscles untouched? It used to be taught that the muscles 

 which straighten the knee, the extensor muscles, contract, 

 and by their contraction exert a moderating influence on 

 the muscles which execute the flexion. That was the 

 anatomical speculation deduced from simple dissection of 

 the musculature of the dead limb. Experiment with the 

 living limb teaches that nature does not expend her 

 muscular energy in using the power of one muscle simply 

 to curb the power of another. When the knee is bent 

 the reflex act does not hamper the working of the flexor 

 muscles by causing a contraction of the extensors also. 

 _Nor does it simply leave the extensors out of account. No ; 

 it causes them to relax and lengthen at the same time as 

 it causes the fle.xor muscles to contract and shorten. This 

 it does by reflex inhibilion ; and it proportions the grade 

 of this relaxation exactly to the grade of contraction of 

 the opponent muscles. 



The inhibition acts, not on the muscle directly, but on 

 the motor nerve-cells innervating the muscle. These nerve- 

 cells are fong filaments : one end of each lies in the muscle, 

 the other in the spinal cord. The reflex inhibition is 

 exercised upon them at the end which lies in the spinal 

 cord. In the reflex we are considering, the reflex action, 

 besides exciting the motor nerve-cells of the three muscle 

 groups— flexors, abductors, and internal rotators — before 

 mentioned, inhibits the motor nerve-cells of three muscle 

 groups antagonistic to those, namely, the extensors, the 

 •abductors, and external rotators. We see, therefore,' that 

 in even the simple reflex lifting of the foot, almost every 

 one of the many muscles composing the whole musculature 

 of the limb receives from the nervous system a controlling 

 influence, either of excitation to contract or of inhibition 

 \yhich relaxes contraction ; and all this in result of a 

 simple touch of the skin of the foot. The reaction typifies 

 in a simple manner the action of the nervous svstem to 

 knit the heterogeneous powers of the body together into 

 one harmonious whole. 



Thus we see that in these actions when one group of 

 muscles contracts the group antagonistic to it relaxes. 

 This is a fundamental part of the coordination of the act, 

 and its discovery throws a welcome light on the nature 

 of certain maladies. Were the antagonistic group to con- 

 tract at the same time as the protagonist, the desired 

 movement would not result. The movement which then 

 ensued w-ould depend on which of the two muscle groups 

 were the stronger, the protagonist or the antagonist.' .The 

 alkaloid strychnine and the poison produced bv the bacilli 

 which cause the maladv called " lock-iaw " "possess the 

 power of destroying reflex inhibition. What the intricate 

 nature of the process of this inhibition is we do not yet 

 know, but it seems to be the exact converse of the process 

 of excitation, the nature of which is also unknown. 

 Mrvchnme and tetanus-toxin change the process of inhibi- 

 tion into its conver.se, namelv, excitation. If a minute 

 lose of strychnine be administered, the reflex which as 

 \vc saw, causes the limb to bend, now causes the limb to 

 straighten instead. This is because the extensors, when 

 tne tlexors contract, instead of being relaxed bv inhibition, 

 are excited to contraction, and being more powerful than 

 NO. 2007. VOL. 77I 



the flexors move the limb in exactly the opposite direction 

 to that in w-hich it should move in this reflex action. 

 Similarly with the toxin of "lock-jaw." The muscles 

 which close the jaws are much more powerful than those 

 which open them. In the normal act of opening the 

 mouth the relatively feeble opening muscles contract, and 

 the powerful closing muscles are simultaneously relaxed 

 by reflex inhibition. But in an animal or man poisoned 

 with this toxin the normal inhibition of the closing muscles 

 is changed to the exactly opposite process of excitation, so 

 that their contraction results. Against the power of these 

 strong closing muscles the contraction of the weak open- 

 ing muscles can effect little. Each time, therefore, that 

 the sufferer tries to open his jaws to take food or speak, he 

 clenches his jaws instead of opening them — experiencing a 

 torture which, although unaccompanied by physical pain, 

 is inexpressibly distressing ; and the disorder leads to death 

 from inanition. 



But to return to the reflex lifting of the leg, whence wr 

 set out. It was mentioned that in this reflex the linih 

 was not merely lifted, but was slightly rotated inward:, 

 at the hip, and that the thigh was slightly abducted, that 

 is to say, drawn sideways, separating it more from the 

 fellow-limb of the opposite. These accessory movemenlr. 

 have a significance coinciding with much other evidence 

 into which we have not time to enter now. They, together 

 with other evidence, show that this lifting of the leg, so 

 easily produced reflexly, is nothing more nor less than 

 the first movement of the taking of a step. In fact, in 

 our rough and imperfect analysis of this little movement, 

 we have been examining part of the great and extra- 

 ordinarily complex and perfect act which is called walk- 

 ing — or more technically, so as to include the cognate 

 acts of trotting and running — locomotion. A little re- 

 flection will suffice to assure you that included • in the 

 action of locomotion is also that of standing. We are apt 

 to forget that the muscles have a static as well as a 

 kinetic action — that they are the instruments of maintain- 

 ing position, as well as of the execution of movements. 

 Directly we begin to analyse locomotion we see that its 

 basis, as it were, is the position of standing, upon which 

 movements of stepping are, as it were, grafted. Not 

 much is known as yet of how animals and ourselves stand, 

 walk, and run. In these acts, probably, every skeletal 

 muscle in the whole body is concerned. Rheumatism can 

 make us aware of that. A little receptor organ in the 

 ear is a great factor in the whole matter. But of this 

 we may be sure, that foremost in its factors are reflex 

 actions of the limbs. Great economic questions are in- 

 volved in this unravelling of the act of locomotion — all 

 beasts of draught and burden are chiefly useful to us 

 because they can stand, and walk, and run. We can only 

 emplov their powers to full advantage and with due 

 regard to them as they unfold these powers when we shall 

 have learnt something of the way in which these move- 

 ments are conducted and performed. 



The crude and imperfect analysis which I have attempted 

 to outline concerned but one phase of the step of a single 

 limb. In the complete act the other limbs will at the same 

 time be executing other phases of the w^hole cyclic reflex. 

 The neck and trunk are also involved; so, likewise, the 

 head itself. Our imperfect analysis threw sidelights on 

 the nature of the mischief wrought by strychnine-poisoning 

 and the malady "lock-jaw." Interesting and useful 

 though these sidelights may be, more really interesting 

 and valuable would be any light which such analysis, crude 

 as it is, could throw on th.at great norinal process of every- 

 day health, animal (including human) locomotion. 

 Analysis of the reflex movement in unconscious animals 

 seems at the present time the only way by which such 

 knowledge can be gained. 



UNIVERSITY AND EDVCATIONAL 

 INTELLIGENCE. 



CAMBRIDGE. — Lord Rayleigh was on .April lo unanimously 

 elected Chancellor of the University in succession to the 

 late Duke of Devonshire. It is expected that the inaugura- 

 tion and the installation of the new Chancellor will take 

 place during the May term. 



