388 



NATURE 



[May 26, 192 1 



researches of Emil Chr. Hansen. It is now 

 realised not only that many industrial concerns 

 depend for their success on a maintenance of con- 

 ditions favourable to the multiplication of the 

 yeast plant, but also that new fields of interest 

 are unfolded to biologists and students of medical 

 research. A book such as this is a timely addi- 

 tion to our literature, for hitherto we have had to 

 be content with books on the subject of yeasts 

 which had a purely industrial bias. In Prof. 

 Guilliermond's book the whole subject is treated 

 in a comprehensive fashion, and the reader will 

 be able to follow the advances in the subject from 

 different points of view. 



Prof. Guilliermond's " Les Levures " appeared 

 in 1912, but the present book is not a mere trans- 

 lation of the French edition ; it is rather a collabo- 

 ration of Dr. Tanner with the author to produce 

 an English work in which it would be possible 

 to incorporate the new material which has 

 appeared since 1912. The idea is a happy one, 

 but it has its disadvantages from the point of view 

 of the reader. Thus, in the first chapter, in which 

 the morphology and development of yeasts are 

 discussed. Prof. Guilliermond is referred to in the 

 third person, with the result that he becomes both 

 counsel and judge in the estimation of the value 

 of his own researches. There is little doubt as to 

 the value of his contributions, but some of the 

 points that have been raised are of a controversial 

 nature, and not such that all biologists ca-i 

 accept without supporting evidence from indepen- 

 dent investigators. Such, for example, are the 

 heterogamic copulation of yeasts, and the attitude 

 adopted in regard to the nuclear structures of 

 these bodies. Many statements are of an ex parte 

 nature, and raise doubts in the reader's mind as 

 to whether he has heard both sides of the ques- 

 tion. Incidentally, Mr. Wager is referred to by 

 the name of " Wagner " throughout this section 

 of the subject. 



There is a very useful chapter on the nutrition 

 and physiology of yeasts, which concludes with 

 an unexpectedly scanty account of the theories 

 which have been advanced to account for the 

 alcoholic fermentation they induce. This is dis- 

 appointing, for, after all, alcohol is responsible for 

 having brought yeasts to the forefront, and the 

 subject is honeycombed with tunnels of investi- 

 gation. 



On the question of phylogeny it is not possible 

 to share the writer's optimism that matters are 

 now " more settled." It is well established that 

 particular growths of micro-organisms may be 

 side-tracked into exceedingly minute structures 

 which can in such a condition multiply indefinitely, 

 NO. 2691, VOL. 107] 



and apparently never emerge into any other forms. 

 It is a common phenomenon in bacterial cultures, 

 and the present reviewer can vouch for the appear- 

 ance of the phenomenon among some of the higher 

 bacteria. The probability that yeasts are side- 

 tracked offshoots of modern fungi may not be 

 great, but there is sufficient evidence to make this 

 theory not untenable even if some recent work 

 in this direction must be set aside on account of 

 cultural impurities. The chapters on the prac- 

 tical methods that are adopted for the studying 

 of yeasts are somewhat perfunctory. Un- 

 doubtedly the most valuable portion of the book 

 is the short description which is given of all the 

 yeasts known to science. The authors have done 

 for yeasts what Migula in his " System der 

 Bakterien " accomplished for bacteria. We are 

 grateful to them for having accomplished this 

 arduous work. Greater knowledge has resulted 

 in slight changes in the classification, but in essen- 

 tials no striking changes have been effected. 



As a book of reference this publication will 

 remain a standard for some time to come. A 

 warning must, however, be given, due to our 

 imperfect knowledge of the activities of micro- 

 organisms. It must not be taken for granted that 

 the discovery of a yeast in a particular medium 

 necessarily credits or discredits it for changes 

 that occur in that medium ; nor does it follow 

 that if a name is given to a supposedly new species 

 that species has not been named before. We 

 know that several species of bacteria have received 

 each several names, and it is probable that we are 

 suffering from the same malady in the investiga- 

 tion of the yeasts. This, however, is an irregu- 

 larity which a general text-book cannot be ex- 

 pected to rectify. We can say in conclusion tl^at 

 this book ought to be in the hands of all those 

 who are interested in yeasts either from the purely 

 scientific or from the industrial point of view. 



David Ellis. 



Introduction to the Theory of Curves. 



Plane Algebraic Curves. By Prof. Harold Hilton. 

 Pp. xvi + 388. (Oxford : At the Clarendon, 

 Press, 1920.) 285. net. 



DURING the present century there has been a 

 very considerable increase in the number 

 of students of the calculus, and this increase has 

 been accompanied by a change in the character 

 and content of the text-books. In the latter half 

 of last century a considerable section of works on 

 the calculus dealt with the theory of higher plane 

 curves, and students with a liking for geometry 

 were often led on to a fuller study of that theory,, 

 as expounded, for example, in Salmon's well- 



