January 21, 1909] 



NA TURE 



559 



the knee causes,' by stretching the extensor muscle of the 

 knee, a reflex inhibition of the contraction of that muscle ; 

 '.he muscle assumes, in consequence, a greater length. 

 This reaction is termed in the paper " the lengthening re- 

 action." It is shown that the afferent nerve of the 

 extensor muscle itself is absolutely indispensable for this 

 reaction. 



Conversely, there is " a shortening reaction." When 

 the extensor muscle is cither passively or by its own active 

 contraction shortened, there occurs a change in the reflex 

 arc of the muscle itself which makes its tonic length less. 

 The result is that a transient contraction of the muscle 

 becomes prolonged by a persistence of the tonic contrac- 

 tion, and this latter is the shortening reaction which 

 appends itself to the transient contraction, however in- 

 duced. The shortening reaction is, like the lengthening 

 reaction, brought about by the afferent nerve-fibres of the 

 muscle itself ; these in some way regulate and adjust the 

 reflex tonus of the muscle. If the afferent nerve-fibres of 

 the muscle itself are severed, the " shortening reaction " 

 and the long, persistent after-contraction which it effects 

 are entirely wanting in the reactions of the muscle. This 

 is so whether the afferent fibres have been severed only 

 a few days or for three months. 



Attention is directed to the similarity between these 

 proprioceptive reflexes of the extensor muscles as studied 

 in cat and dog and the reactions observed by v. UexkiJll 

 and others in tonic preparations of various invertebrate 

 muscle, e.g. the retractor muscle of Sipunculus. The 

 similarity is close enough to leave little doubt that the 

 phenomena achieve the same practical end. 



Mathematical Snciety. Taniiary 14.— Sir \V. D. Nivtn, 

 president, in the chair. — The canonical form of a linear 

 substitution : H. Hilton. — Researches concerning the solu- 

 tion of the quintic equation : J. Hammond. — Octavic and 

 sexdecimic residuacity : Lieut. -Colonel A. Cunningham. 

 — Change of the variable in a Lebesgue integral : Dr. 



E. W. Hobson, — Abel's extension of Taylor's series : Rev. 



F. H. Jackson. — N'ote on the evaluation of a certain 

 integral containing Bessel's functions : Prof. H. M. 

 Macdonald. 



M.ANCHESTER. 



Literary and Philosophical aocity. Decern! er 15, 1908. — 

 Prof. H. B. Dixon, F.R.S., president, in the chair. — The 

 volatility of radium A and radium C : W. Makower. The 

 experiments described were carried out with a view to deter- 

 mine the volatility of radium A, and also of re-determining 

 that of radium C under different conditions to see whether 

 the volatility of this product was influenced by its environ- 

 ment. The volatilisation point of radium A was found to 

 be goo° C. Radium C was found to begin to volatilise 

 at a temperature between 700° C. and 800° C. When 

 deposited on a platinum or nickel surface the volatilisation 

 was found to be complete at 1200° C, whereas when de- 

 posited on quartz the volatilisation was still incomplete 

 even at 1300° C. The same result was found whether the 

 deposit had been previously dissolved in hydrochloric acid 

 or not. Finally, experiments were made to see whether 

 radium C is charged at the moment of its production from 

 radium B. Experiments in which the emanation exposed 

 to an electric field was contained in a furnace at 950" C. 

 failed to reveal any evidence of a charge carried by 

 radium C. — Note or. the production of white ferrous ferro- 

 cyanide : R. L. Taylor. A little solution of either hydro- 

 sulphurous acid or of sodium hydrosulphite, added to a 

 solution of ordinary ferrous sulphate, frees the solution so 

 completely from any trace of a ferric salt that it gives a 

 pure white precipitate with potassium ferrocyanide, instead 

 of the light blue precipitate usually obtained. The white 

 precipitate rapidly turns blue when exposed to the air, and 

 it is also instantly turned blue when ordinary tap-water 

 is added to it. owing to the oxygen which is dissolved in 

 the water. Water which has been previously well boiled 

 to expel dissolved air does not alter the colour of the pre- 

 cipitate. Hydrosulphurous acid or sodium hydrosulphite 

 will turn Prussian blue perfectly white. 



January 12. — Prof. H. B. Dixon, F.R.S., president, in 

 the chair. — The influence of light on the coloration of 

 certain marine animals (Hippolyte, Wrasses) : Dr. F. W. 

 Gamble. The author gave an account of his work on 



NO. 2047, VOL. 79] 



the colour-physiology of Hippolyte (the ^sop-prawn), and 

 of one of the common British wrasses (_Crenilabrus melops). 

 Hippolyte is a variably coloured prawn, each colour variety 

 agreeing closely with the tint of the weed on which it is 

 found, and upon which it feeds. Previous experiments 

 made jointly by the author and Prof. Keeble have shown 

 that this remarkable sympathetic coloration is in all 

 probability not inherited — i.e. the colour varieties do not 

 necessarily breed true, but that the harmonious motley 

 exhibited by this varying species is the outcome of a very 

 special colour adaptation undergone by each individual, 

 and that the coloration is controlled largely by the colour 

 of the weed at the time when the young prawn settles 

 down upon it, after a brief free-living larval existence. 

 The results of more recent researches by the author on 

 this subject have shown that the amount of pigment in 

 the larva varies, in all races but the green one, with that 

 in the parent. The more there is of it in the parent, the 

 niore highly coloured is the offspring. Green parents, 

 however, gave rise to three kinds of broods : — (i) highly 

 coloured ones like those of brown parents ; (2) pale ones ; 

 and (3) a mixed brood, containing coloured to colourless in 

 the proportion of 3:1. Coloured light experiments yielded 

 an unexpected result, namely, a complementary colour to 

 that of the light employed. Thus, under the influence of 

 green light for a month, Hippolyte lost its yellow pig- 

 ment and became brilliantly scarlet, while under red light 

 it became green. In both cases the animal at starting 

 was of a transparent and almost colourless appearance. 

 The value of this complementary colour production (which 

 does not appear to have been recognised in animals pre- 

 viously) upon the problem of the coloration of Hippolyte 

 was briefly discussed. 



Paris. 

 Academy of Sciences. January 11.— M. Bouchard in the 

 chair.— The families of Lam6 resulting from the displace- 

 ment of a surface which remains invariable in form : 

 Gaston Darboux.— A general method of preparation of 

 the monoalkvl, dialkyl, and trialkyl-acetophenones : A. 

 Haller and Ed. Bauer. The ketone (methyl, ethyl, or 

 propylphenvlketone) is dissolved in pure dry benzene, an 

 equimolecular proportion of finely divided sodium amide 

 added, and heated on the water bath until a clear solution 

 is obtained. The alkvl bromide or iodide is added drop by 

 drop to this solution. By this method the following 

 ketones have been prepared and their properties given m 

 detail -—trimethvlacetophenone, ethyldimethylacetophenone, 

 methvldiethylace'tophenone, triethylacetophenone, methyl- 

 ethvlpropylacetophenone, and allyldimethylacetophenone.— 

 Dirichlet's series: Harald Bohr.— The double integrals of 

 the first species attached to an algebraic variety : Francesco 

 Severi.- A theorem on differentials : W. H. Young.— A 

 particular critical point of the solution of the equations 

 of elasticity in the case where the forces on the border 

 ire rtiven " A. Korn.— The theorv of the moon : H. 

 Andoyer.— A dynamometer for testing motors with large 

 angular velocity : M. Ringelmann. The defects of the 

 Pronv brake for testing high-speed motors are reviewed 

 and K new form of dynamometer described, by means ot 

 which the total energy furnished at each instant by the 

 motor can be read offi and is at the same time recorded. 

 —A formula for velocity applicable to propulsion in air : 

 Alphonse Berget. A modification of a formula devised 



where V is 



4/|- 



for the velocity of steam vessels. V = C 



the velocity in mvriametres per hour, F the horse-power, 

 S the surface of maximum section of the balloon in 

 square metres, and C the coefficient of utilisation. The 

 latter is shown to vary between 30 and 5-0 for various 

 types of steerable balloon.— The radiation of cerium 

 oxide: M. Foix. Some experiments are cited in support 

 of the theoretical relation given in an earlier paper.— A 

 modification of the phonograph : M. de Pezzer.— Aqueous 

 solutions of pyridine: E. Baud. The freezing points ot 

 aqueous solutions of pyridine varying in concentration 

 from :; per cent, to 100 per cent, are given. The densities 

 and refractive indices of these solutions were also 

 measured, and also the heat of solution of pyridine in_ a 

 large excess of water. Only two hydrates of pyridine, with 

 two and six molecules of water, are indicated by these 



