December 22, 1921] 



NATURE 



529 



duced Japanese pearls, while the fact that culture 

 pearls produced in other localities, or in other species 

 or races of pearl oysters, will probably be indistin- 

 guishable from naturally produced pearls from the 

 same sources is not mentioned. 



It is a significant fact that the English pearl mer- 

 chants and jewellers have apparently made no attempt 

 to obtain and publish scientific opinions on the 

 problems raised by the coming of the "culture pearl." 

 This will probably prove in the end a shortsighted 

 policy. It is quite likely that the values of the stocks 

 of "natural " pearls which are held by merchants and 

 others will suffer very much more from the uncer- 

 tainty and confusion which are created by statements 

 like those referred to here than they would have 

 suffered from a full and frank explanation to the 

 public of the exact nature, and probable future 

 developrnent, of the Japanese discovery. This dis- 

 covery, important as it is as a scientific achievement, 

 need not have produced the panic which, to judge 

 from their behaviour, seems to prevail in certain sec- 

 tions of the precious stones trade. If at the outset 

 the merchants and jewellers had acted as realists 

 instead of behaving (and thinking they could induce 

 the public to behave) in the manner so often wrongly 

 attributed to the ostrich, it Is quite likelv that the 

 pearl market would by this time have adjusted Itself 

 to the change. ' H. Lyster Jameson. 



A Curious Physiological Phenomenon. 



At a recent meeting of biologists at Strasbourg 

 Messrs. A. Schwartz and P. Meyer directed attention 

 to the curious physiological phenomenon which is 

 shown by the following experiment : — 



With arms hanging relaxed, stand about i8 In. 

 from any solid structure, such as a wall, and face 

 the direction parallel to the wall. Stiffen the arm 

 next the wall and move It away from the body until 

 the back of the hand comes Into contact with the 

 wall; stand firm and press the wall as hard as pos- 

 sible with the back of the hand for about 15 seconds. 

 Now relax the arm, step away from the wall, and this 

 Is what will happen : 



To the observer's astonishment, his arm will slowlv 

 rise, without his making any voluntarv effort, until 

 It reaches an approximately horizontal position; it 

 will remain there for a few seconds and {hen fall 

 back. Whilst the phenomenon is taking place the 

 observer has the sensation that his arm Is raised bv 

 an exterior force which is quite Independent of voli- 

 tion. Anyone interested in the explanatory theories 

 put forward by the above-mentioned gentlenien should 

 consult the Comptes rendus de la Societe de Biologie, 

 vol. 85, No. 27, July 23, 1921, p. 490. 



F. C. D.ANNATT. 



198 Rue Saint-Jacques, Paris (56), November 28. 



I FIRST came across this phenomenon In 1917, when 

 It was shown as a "parlour trick " In an officers' mess 

 In Macedonia. It Is obviously of the greatest Interest, 

 but I was unable to trace it to its origin. 



To the description in Mr. Dannatt's letter mav be 

 added the observation that the movement ensues even 

 where the subject has no knowledge of what is about 

 to occur — my first personal experience of the pheno- 

 menon occurred before I was told what to expect. 

 This Is of Importance, for it removes possibilltv of 

 "suggestion." The phenomenon is a physiological 

 one. 



Any explanation at present must be purelv hypo- 

 thetical. The "voluntarv" movement of a limb is 

 brought about through the activity of the " motor " 

 area pyramidal cells in the cortex of the great brain. 

 NO. 2721, VOL. 108] 



Such reactions (under experimental conditions) are 

 often followed by the opposite form of movement — 

 e.g. flexion by extension (Graham Brown and 

 Sherrington, Proc. Roy. Soc, B, vol. 85, p. 250, 

 1912). But the peculiarity of the present movement 

 is that It is in the same direction as the original 

 one. That is, the upper limb is pressed against the 

 wall in a voluntary manner ; after a few seconds' 

 rest it is raised towards the wall in an involuntary 

 manner. After-discharge of the same movement may, 

 however, also occur under experimental conditions 

 (called ' tonus remainder " by the above investigators). 

 But this involuntary movement of the arm occurs 

 after a distinct pause. 



The curious lack of "volition" whilst the arm is 

 rising might be explained (on the assumption that the 

 movement Is due to an after-discharge of the motor 

 cortical area) if the feeling of voluntary fatigue 

 depends upon functional changes a step back in the 

 cerebral path. Thus the motor cells are set into 

 activity by other nerve cells. If the fatigue of volition 

 occurs in these other cells, and the after-discharge in 

 the motor cells themselves, the absence of a feeling 

 of "voluntary effort" might be explained. 



The movement — the slow. Involuntary rise of the 

 arm — is, however, not like those obtained from the 

 motor area of the great brain when it is stimulated. 

 But it is like the movements obtained from another 

 motor mechanism — that of the "red nucleus" and 

 other structures In the mid-brain and hind brain. I 

 think that the phenomenon is far more likely one 

 brought about by this other motor system, which is 

 essentially concerned in the slow " postural " move- 

 ments and maintained postures of the body (Graham 

 Brown, Proc. Roy. Soc, B, vol. 87, p. 145, 

 19 13). It is more than likely that the two 

 motor mechanisms combine In directing muscular 

 activities — sometimes reinforcing one another, some- 

 times inhibiting. If this is the case, the 

 pressing of the arm against the wall may be 

 brought about by both mechanisms, the drop of the 

 arm at the end of the voluntary act may be an addi- 

 tional voluntary act, and the after-discharge of the 

 " red nuclear " mechanism (to give It a too restricted 

 name) may later reassert itself. Or the "motor area " 

 activity may from the first inhibit the "red nuclear," 

 and when the former Is "fatigued" the latter may 

 assert Itself In a "rebound " from Its state of inhibi- 

 tion. 



Enough has been said to indicate our Ignorance of 

 the conditions which might explain the phenomenon 

 and to show how speculative any explanation must be 

 at present. One last suggestion may be made. The 

 phenomenon may be related to the curious maladjust- 

 ment of movement which occurs after a heavy weight 

 has been carried for a distance and then abandoned. 

 Everyone who has carried a heavy knapsack for a 

 distance and then laid it down knows how his first few 

 steps without it are unbalanced. 



T. Graham Brown. 

 Physiology Institute, Universitv College, Cardiff, 

 December 8. 



Echinoderm Larvae and their Bearing on Classification. 



Ix Nature of December 8 there appears an article 

 by my friend Dr. F. A. Bather entitled "Echinoderm 

 Larvae and their Bearing on Classification." The 

 article consists of a review of Dr. Mortensen's work 

 entitled " Studies of the Development and Larval 

 Forms of Echinoderms," and In the course of the 

 article Dr. Bather quotes with apparent approval 

 some remarks of Dr. Mortensen to which I desire 

 to take the strongest exception. 



