NATURE 



[July 6, 191 1 



Fliirscheim, and Obermiiller are shown to be funda- 

 mentally untenable or self-contradictory. The author 

 concludes : — 



"Das Endergebniss unserer theoretischen Betracht- 

 ungen ist kein erfreuliches ; alle Versuche, welche bis 

 jetzt gemacht sind, um die Gesetzmassigkeiten, welche 

 den Ort bestimmen, wo ein zweiter Substituent im 

 Kern eintritt, zu ergriinden, sind vollkommen fehl- 

 geschlagen ; ja selbst ist es nicht moglich gewesen, 

 die Tatsachen in einer empirischen Regel zusammenzu- 

 fassen." 



After discussing the position taken up by the third 

 entrant group in chapter v., the author develops his 

 own views on the mechanism of substitution. These 

 views, which are published here for the first time, 

 are so eminently simple and rational that chemists 

 may be interested in the following brief outline. Fol- 

 lowing Kekule's idea that substitution is a succeeding 

 phase of an additive process, Prof. Holleman con- 

 siders that such a process as nitration, for example, 

 of a compound containing a substituent X produces in 

 the first place one or more of the following three 

 substances : — 



HO X 



HO X 



H NO, 



NO/I || 



X 

 H 



H 



OH 



< H 



NO., 



from which the elements of water are subsequently 

 detached. The nature of the predominating com- 

 pound or compounds will be determined by the 

 accelerating or retarding influence of the substituent 

 X, just as addition of bromine to an define will be 

 determined by the substituents already present. If X 

 accelerates the reaction of ortho and para, substitu- 

 tion will be the main result, if it retards, meta sub- 

 stitution (where the double link is unconnected with 

 the X complex) will be the primary effect. If X has 

 no marked effect meta and ortho, meta and para, or 

 all three may be formed. 



A work of this kind, which, the author tells us, 

 necessitated the careful perusal of upwards of a 

 thousand original papers, ungrateful and laborious as 

 the task of compilation may have been, will always 

 remain a standard book of reference, for which 

 chemists will feel fully grateful to the author. 



J. B. C. 



FERMENTS AND FERMENTATION. 

 Micro-Organisms and Fermentation. By A. Jorgen- 



sen. Translated by S. H. Davies. Fourth edition, 



completely revised. Pp. xi + 489. (London: C. 



Griffin and Co., Ltd., 1911.) Price 15s. net. 

 TN this translation of the fifth German edition 

 -L (dated January, 1909) of his well-known text- 

 book, the author has incorporated the main results of 

 investigations made since the appearance of the pre- 

 vious English edition about ten years ago. Although 

 the book has been, to a considerable extent, re- 

 written, its original characteristics are retained. 



Five of Ihc six sections of the work have been 

 NO. J 175, VOL. 8/] 



enlarged, whilst the sixth, dealing with the pure 

 culture of yeast on a large scale, has undergone 

 marked reduction in volume, possiblv because it forms 

 the subject of a separate publication by the author. 

 The illustrations have been increased in number from 

 83 to 101, nearly all of those found in the previous 

 edition being again given ; most of the figures are 

 good, but those numbered 12, 13, and 51 would un- 

 doubtedly bear improvement, while Fig. 80 fails to 

 bring out the peculiar bean- or kidney-shape of the 

 spores of Saccharomyces fragilis.. The bibliography 

 has been revised and supplemented ; it is, however, 

 questionable whether a bibliography placed at the 

 end of the book is more convenient than references 

 given as footnotes to the text. One new feature, 

 which will be welcomed by all readers, is the pro- 

 vision of an alphabetical index of subjects. 



As the author is a member of the Danish school of 

 micro-biologists, the book would naturally be expected 

 to give, as in reality it does, a prominent place to the 

 investigations of Hansen and his followers on the 

 micro-organisms met with in the brewing industry. 

 At the same time, the more important researches car- 

 ried out during recent years in Germany and elsewhere 

 are not, as a rule, lost sight of, although no reference 

 is made to the valuable work of Slator on alcoholic 

 fermentation, while the meagre notices given to the 

 results obtained by Ehrlich and by Harden and Young 

 might have been replaced profitably by more extended 

 discussions. 



The first chapter, headed " Microscopical and Physio- 

 logical Examination," deals with such subjects as 

 staining, sterilisation, antiseptics, nutritive substrata, 

 and pure culture methods. In this section the space 

 devoted to technique is very small, and a more detailed 

 description of the methods employed in the author's 

 laboratory would have been of value. In the part 

 dealing with nutritive media, no mention is made of 

 "eau de touraillons," which furnishes an excellent 

 basis for such media, and is largely employed by some 

 of the French investigators. Attention is directed to 

 the stimulating action of small proportions of various 

 poisons on the growth of micro-organisms, but no 

 reference is made to the very thorough researches 

 of Javillier on the influence of zinc on the growth of 

 vegetable organisms, including moulds. 



Chapter ii. treats of the biological examination of 

 air and water, chiefly from the point of view of brewery 

 requirements. 



In chapter iii., the functions and conditions of 

 growth of zymogenic bacteria are described. A para- 

 graph is given to the nitrifying bacteria, but nothing 

 is said of the very important class of nitrogen-fixing 

 bacteria. 



The moulds form the subject of chapter iv., which 

 also deals incidentally with enzymes and with the 

 influences of various external conditions on micro- 

 organisms in general. The occurrence and life-history 

 of most of the commoner moulds arc studied, and 

 reproductions are given of some of the excellent draw- 

 ings made by Brefcld and de Bary. 



The fifth chapter, occupying nearly two hundred 

 pages, is concerned with the yeasts, and deals, in 

 addition, with non-sporulating or Torula forms, as 



