October i8, igob] 



NATURE 



627 



Among the birds the ostrich is p«culiar, owing to the fact 

 that there is no communication between the posterior and 

 superior canals at the point at which they cross. The 

 cochlea is also very short. The crested screamer has a 

 relatively long cochlea, and the superior canal droops some- 

 what backwards. • 



May 10. — " The Mechanism of Carbon .Assimilation in 

 Green Plants : the Photolytic Decomposition of Carbon 

 Dioxide Ui vil'o. By K. L. Usher and J. H. Priestley. 



For summary of this paper see Naturk of October 11 

 (p. 1104). 



June 14. — "'Studies on Enzyme Action. Lipase, 11." 

 By Prof. Henry L. Armstrong, F.R.S., and Dr. Ernest 

 Ormerod. 



Inasmuch as the ethereal salts which are hydrolysed 

 under the influence of lipase are all compounds of the type 

 R'.CO.OX', it cannot well be supposed, as R' and X' 

 may be varied within wide limits, that the selective action 

 of the enzyme is exercised with reference either to R' or 

 to X' : consequently the controlling influence must be 

 ailribuled to the carbo.xyl radicle (CO.O) ; the enzyme 

 must be so constituted that it can " fit itself to this group." 

 The problem to be solved is — why should ethereal salts 

 derived from the lower terms of the acetic series be so 

 much less readily hydrolysed than the higher? The 

 ditiferences in stability do not accC'Unt for the differences in 

 behaviour of homologous salts ; in fact, ordinary hydrolytic 

 agents appear to act more readily on the lower terms. 

 Nor can the difference be attributed to the destruction of 

 the enzyme by the acid which is liberated from the salt, 

 as this destructive effect can be avoided by diluting the 

 solutions to the necessary extent. Their experiments have 

 led the authors to fortii the provisional hypothesis that the 

 hydrolysis of the ethereal salt by lipase involves the direct 

 association of the enzyme with the carboxyl centre and 

 that such association may be prevented by the " hydra- 

 tion " of this centre : consequently, that those salts which 

 are the more attractive of water will be the less readily 

 hydrolysed. The facts generally seem to be in accordance 

 with this view, inasmuch as the solubility in water of 

 ethereal salts diminishes as the series is ascended ; salts 

 such as ethyllc formate and acetate undoubtedly tend to 

 form h^'drates (hvdrols) in solution, such as • 



CH;,.CO. OEt + OH, = CH.,.CfnEi ) 



OR 

 OH- 



A noteworthy result in harmony with the view is the 

 fact that ethylic malate is but slowly acted upon bv lipase 

 in comparison with ethylic succinate and that ethylic 

 tartrate is practically unaffected. The explanation of the 

 differences to be observed between animal and vegetable 

 lipase is probably to be sought for rather in differences in 

 their emulsifying power than in peculiarities inherent in 

 the lipoclast. The main difficulty the investigation pre- 

 sents lies in securing uniform conditions : if an effective 

 comparison is to be made between ethereal salts, it is an 

 essential condition of success that the substances compared 

 be in solution. Peculiar difficulties are encountered on this 

 account in studying the action of lipase from various 

 sources on fatty substances. 



June 21. — " Ionic Velocities in .\ir at different Tempera- 

 tures." Bv P. Phillips. Communicated by Prof. J. J. 

 Thomson, F.R.S. 



The object of this paper is to find at different tempera- 

 tures the velocity in an electric field of the ions produced 

 by Rontgen rays in air at atmospheric pressure. The 

 method used for determining the velocities is that devised 

 by Langevin in !Q02, and published in his " Recherches 

 sur les Gaz ionis^es," Paris, T902. 



The general arrangement of the apparatus is very little 

 different from that used by Langevin, the only serious 

 difference being that the vessel containing the electrodes 

 is made so that it may be immersed in baths at different 

 temperatures. 



The velocities have been found at temperatures ranging 

 from — lyq" C. to -1-138° C, and the following are the 



N'^. 1929, VOL. 74] 



values of /;, and U,, the velocities of the +vii and —ve 

 ions under a field of one volt per centimetre : — A 



2 00 



I 95 

 1-85 

 I -Si 

 1-67 

 I 60 

 '■39 

 0945 

 0-235 



2-495 

 2-40 

 2-30 



2-21 

 2125 

 2 00 



1-785 

 1-23 



0-235 



Ttmp., abs 



,.. 411 



••• 399 



- 383 



- 373 

 ... 348 



•• 333 



.. 285 



... 209 

 ... 94 



When />;, and />-, are plotted against the temperature we 

 see that between the temperatures 200° and 411° /c, and 

 /.', seem to be proportional to the absolute temperature, but 

 at 94" fc| and fe, seem to be equal, and much smaller 

 than would be given by this linear law. 



-Making use of the kinetic theory of gases, we can arrive 

 at the following expression for /c, and fe„ : — 



-■["(--n-^:)']' 



where X is the field in absolute units, e the charge on 

 the ion, A. the mean free path of a molecule, m the mass 

 of a molecule, v the mean molecular velocity of the mole- 

 cule, and H the number of molecules in an ion. Making 

 use of the values of fe, and fe, given above, we obtain the 

 following values of », and 11, : — 



Tenip. , abs ;/j « 



94 4-63 4-63 



209 ... 2-12 ... 1-82 



285 1-76 1-43 



348 1-64 1-34 



411 1-52 1-25 



When n, and 11, are plotted against the temperature they 

 show a very rapid increase as the temperature of lique- 

 faction of air is approached. This is what might be 

 expected, as the ions in a vapour near its liquefaction 

 temperature are usually large. .At the upper temperature 

 the curve shows no very marked tendency, so that it is 

 difficult to predict what might happen at a higher tempera- 

 ture. 



The fact that n varies continuously, and not in jumps, 

 would seem to show^ that there is a continual exchange 

 going on between ions and uncharged molecules ; at some 

 collisions several molecules remain attached to the ion, 

 while at others one or more of them is knocked off, and 

 so a dynamical equilibrium is set up. .As the temperature 

 of the gas rises, the collisions are more violent, and, 

 statistically, fewer molecules are attached to an ion : this 

 gradual change would go on until the collisions became 

 so violent that at times corpuscles would be shot off with- 

 out even a single molecule attached to them. When this 

 happened the velocity of the ion would very rapidly increase 

 with the temperature, and so we might expect in flames 

 those very rapidly moving ions which consist of single 

 unloaded corpuscles for an appreciable fraction of their 

 existence. 



" Note on Opalescence in Fluids near the Critical 

 Temperature." By Prof. Sydney Young:, F.R.S. 



The e.xperiments described by Travers and Usher were 

 mostly carried out at constant volume, the temperature 

 being raised very slowly. In the author's experiments 

 the substance was kept at its critical temperature, and the 

 volume altered by equal stages. The tubes employed were 

 much narrower. Where comparison is possible the observ- 

 ations confirm those of Travers and Usher, and the follow- 

 ing generalisations may be deduced from them : — (i) When 

 observations were made during compression no opalescence 

 was visible until a definite volume was reached : opal- 

 escence then appeared at the bottom of the tube, that is 

 to say. just over the mercury ; on further compression the 

 opalescence or inist became denser, and extended further 



