October 13, 1923] 



NATURE 



533 



aberrations of photographic objectives, which has been 

 recently adapted to microscopic objectives also. 



Reference may now be made to one other part of the 



dioptric mechanism, namely the " accommodation." 



iOf this Dr. Troland writes (p. 40) that Helmholtz's 



theory " borders on the line between legitimate infer- 



[ence and mere hypothesis." In this connexion we 



Imay recall that many physiologists hold Tscherning's 



theory to be the correct one. In fairness to the 



^memory of Helmholtz, it should, however, be stated 



[that several recent workers have obtained results 



[wholly in favour of his view. 



Of the retina, and the nature of the processes by 

 which light and colour are perceived, Dr. Troland 

 writes (p. 43) : "It is to be regretted that relatively 

 little work upon the microscopic anatomy of the retina 

 has been done in recent times, the epoch-making re- 

 searches of Raman y Kajal having found no worthy 

 successors." With this opinion every physiologist must 

 regretfully agree ; but will there be such unanimity 

 over Dr. Troland's dismissal of Edridge-Green's theory 

 in the following words ? — " Views such as those of 

 Edridge-Green, who regards the rods as non-photo- 

 sensitive manufacturers of visual purple, which latter 

 is operative only in stimulating the cones, may be dis- 

 missed at once without serious consideration." Now, 

 however difficult it may be for some of us (who have 

 been, as it were, brought up on the duplex theory of 

 von Kries, which teaches that the rods function in 

 night vision, and that while the hen has no rods and 

 is therefore night blind, the bat has no cones and is 

 therefore day blind) to accept Edridge-Green's hypo- 

 thesis, we must feel that to dismiss it without con- 

 sideration is to act too impulsively. 



The criticisms which Edridge-Green advances against 

 the older view are very weighty and worth serious 

 thought. It is possible that, as so often in physiology, 

 parts of both views are true and that there may be 

 some half-way hypothesis acceptable to both parties ; 

 such, for example, 'as this : that while cones function 

 principally by day for the appreciation of colour, and 

 rods by night, yet cones do function to some extent at 

 night, by a partial retention of the old functions of the 

 rods from which they were presumably developed, 

 while, on the other hand, rod vision is still to some 

 extent operative in day vision, particularly in regions 

 of the retina, on which are falling parts of the image 

 corresponding to the shadows. It is only by dismiss- 

 ing nothing without consideration, and by research on 

 the lines of Kuhne and of Hecht, that this important 

 problem will be finally solved. 



Much the same statement must be made concerning 

 the appreciation of colour. New hypotheses, based on 

 the quantum theory, are springing into being, and there 



NO. 2815, VOL. 112] 



are not sufficient data to enable a decision to be made 

 between them and the older trichromatic theory of 

 Young. Colour mixture equations would suggest that 

 there are pigments present in the retina other than 

 visual purple, but there is great need of direct proof 

 of their existence and quantitative information con- 

 cerning their distribution in the retina and their 

 spectrophotometric properties. It is not the repetition, 

 which Dr. Troland advocates, of older work that is 

 wanted so much as entirely new lines of attack. 



Many other important branches of visual science are 

 dealt with by Dr. Troland in his book, but enough has 

 been written here, perhaps, to show that the volume 

 is a very real contribution to knowledge. No better 

 incentive to future research could have been compiled ; 

 let us hope that the harvest will be a rich one. 



H. Hartridge. 



The Brackish-water Area of the Zuiderzee. 



Flora en Fauna der Zuiderzee. Monografie van een 

 Brakwatergebied onder redactie van Dr. H. C. 

 Redeke en met medewerking van Tera van Benthem 

 Jutting, H. Engel, H. C. Funke, Dr. A. C. J. van 

 Goor, J. A. W. Groenewegen, Dr. B. Havinga, 

 J. Hofker, Dr. R. Horst, Prof. Dr. P. N. van 

 Kampen, Geertje de Lint, Dr. J. G. de Man, Prof. 

 H. F. Nierstrasz, Dr. A. C. Oudemans, Prof. Dr. 

 C. Ph. Sluiter, Dr. J. F. Steenhuis, Dr. J. J. Tesch, 

 Dr. Adriana Vorstman, Nel de Vos, Prof. Dr. Max 

 Weber en Dr. N. L. Wibaut-Isebree-Moens. Uitge- 

 geven door de Nederlandsche Dierkundige Vereeni- 

 ging ter Gelegenheid van Haar Vyftigjarig Bestaan. 

 Pp. 460. (Helder: C. de Boer, Jun., 1922.) 10 

 guilders ; for members of the Nederl. Dierk. Vereen., 

 f. 2.50. 



WITH the draining of the Zuiderzee one of the 

 largest brackish-water basins of Europe, and 

 a very peculiar one, will disappear. In the Baltic 

 Sea, the largest of all, tidal movements are of very 

 little importance : in the French and English river- 

 estuaries, tides are the predominating factor, while 

 in the Zuiderzee only a few small areas are struck by 

 regular tidal currents, and the greater part of the 

 southern basin is only shaken up from its lake-dreami- 

 ness by north-western gales. Therefore it was a very 

 useful work of the Dutch Zoological Society (Neder- 

 landsche Dierkundige Vereeniging), and specially of 

 Dr. H. C. Redeke, the director of the Zoological Station 

 in Den Helder, to bring together all that is known from 

 the Zuiderzee in this monograph, issued on the occasion 

 of the fiftieth anniversary of the Society. 



In recent years a few small expeditions have been 



P I 



