July 30, 1903] 



NATURE 



291 



" cusses the position of their colouring matter and 



'i ascribes the waterproof character of certain cell mem- 



i branes to the deposition of excreted fatty or waxy 



jl substances, pointing- out that this waterproof character 



I is of importance biologically, 



F " since it prevents the penetration of toxic substances 

 I from the surrounding aqueous medium, and thereby 

 also opposes the attempts of the mycologist to kill such 

 fungi by means of aqueous toxic solutions." 



A chapter is devoted to the mineral nutrient matter 

 milised by the Eumycetes, the author indicating that 

 \ certain substances which are not absolutely neces- 

 f sary for the nutrition of these organisms may still, as 

 '% in the case of nickel, cobalt, and manganese, like iron, 

 \ exert a stimulative action on the growth of fungi. 

 Sulphur, selenium, and silicon may also be found in 

 the protoplasm of these fungi, but phosphorus appears 

 to be a most important element in their composition, 

 and, although arsenic does not take the place of the 

 phosphorus in the Eumycetes, certain of these or- 

 ganisms appear to have the power of converting 

 arsenious acid into volatile compounds having an 

 odour of garlic. These organisms have, therefore, 

 been used for the purpose of indicating the presence 

 of arsenic in cases where, by the ordinary Marsh's 

 tests, only a doubtful reaction has been obtained. 

 The influence of light on the development of the 

 Eumycetes is discussed, and it appears that although 

 strong light interferes with their development, 

 moderate illumination interferes very little with their 

 activity. Chemotropism is discussed somewhat frag- 

 mentarily; this remark applies also to the diastatic 

 enzymes and the enzymes capable of decomposing fat ; 

 the enzymes of yeast, however, are described more 

 fully in the later part of the work. 



The special part of the book consists of two sections, 

 one devoted to the fermentation set up by Zygo- 

 mycetes, the other to a preliminary consideration of 

 yeast-fermentation. The first of these sections is 

 interesting to the technologist from the fact that 

 it deals with Calmette's Amylomyces Rouxii or Mucor 

 Rotixii, derived from the Chinese yeast-balls used in 

 the preparation of rice spirit. This produces a 

 powerful diastatic enzyme which first produces glu- 

 cose, and this, in the absence of oxygen, is converted 

 by yeast ferment into alcohol. For a full account 

 of the Amylomyces process the reader may be referred 

 the description of the use of the Mucoreas in the 

 lit industry. 



I he latter half of part i. of vol. ii. is devoted entirely 

 yeasts, especially the forms, structure, and chemical 

 . imposition of the yeast-cell, and anyone who studies 

 this will be amply repaid by obtaining a knowledge 

 <f the principles and mechanism of fermentation such 

 can be obtained elsewhere only by the study of 

 ilky treatises, though now and again one is a little 

 disappointed that the author has not elaborated his 

 descriptions somewhat more fully, this remark apply- 

 ing specially to the chapter on the chemistry of the 

 yeast-cell. The sketch given is so interesting that one 



Ijwould have welcomed a somewhat more detailed 

 iiccou'nt of this part of the work. 

 I After reading this work one feels the truth of 

 Hansen's statement that none of the text-books and 



manuals giving a summary of larger or smaller 

 sections of technical microbiology has treated the 

 subject of this extensive field from so comprehensive 

 a point of view as that of Dr. Lafar. In preparing 

 the work, the author has exhibited not only many 

 sided discernment and enthusiasm for his task, but 

 also great courage and endurance. Certainly, this 

 part of the second volume 



" will be welcomed not only by those for whom it is 

 primarily intended, viz., technical chemists, chemists 

 dealing with food stuffs, fermentation and agricul- 

 ture, pharmacists, and agriculturists, but many 

 another worker will derive benefit from its pages for 

 his lectures and researches." 



We can cordially recommend this section of Dr. 

 Lafar 's work as an excellent supplement to the first 

 volume, which has already been reviewed in our 

 columns. 



We are glad to learn that the translators have made 

 arrangements with the German publishers to obtain 

 advance proofs of the German work in order that the 

 concluding sections may appear as soon as possible. 

 This portion of the work fully maintains the interest 

 aroused by the first volume, and the translators are 

 to be congratulated on the fact that they have been 

 able to give so accurately not only the substance, but 

 the spirit of the German work. 



G. Sims Woodhead. 



VISUAL PURPLE. 

 Abhandlungen eur Physiologie der Gesichtsempfind-- 

 ungen. By J. von Kries. Heft, i., 1897, pp. vi4- 

 198; Heft, ii., 1902, pp. 197. (Leipzig: johann 

 Ambrosius Barth.) 



THIS is a collection of papers reprinted from the 

 Zeitschrift fiir Psychologic und Physiologie 

 der Sinnesorgane. The papers are the work of voa 

 Kries and his school, and deal chiefly with visual 

 purple and its functions. They give an account of one 

 of the most important of recent advances in our know- 

 ledge of the physiology of sensation. 



The discovery of visual purple in 1876 aroused great 

 hopes, which seemed to be frustrated when it was 

 found that the substance was absent from the fovea, 

 the place of most distinct vision, and physiologists 

 soon settled down to the view that a substance absent 

 from this situation could have little to do with the 

 production of visual sensations. 



In the early days, however, Kiihne suggested that 

 the great instability of visual purple made it probable 

 that it was a substance for the perception of feeble 

 light, and Parinaud in France later advanced the same 

 idea. It has been reserved for von Kries to develop 

 fully Kiihne 's idea. 



According to von Kries, visual purple is a substance 

 which supplies the retinal basis for vision at low 

 luminosities, and the accumulation of this substance 

 is accountable for the great increase in sensitiveness 

 of the dark-adapted eye — a thousand-fold increase 

 according to some computations. 



The change in the relative brightness of different 

 colours with varying illumination, first pointed out by 

 Purkinje, finds a ready explanation on this view. 



