VI PREFACE. 



leave various problems undiscussed. On the other hand, 

 repetition could not always be avoided for the sake of young 

 students, when similar subjects were discussed in different 

 sections. 



Among the many new questions demanding fuller treatment 

 in this, the fourth English edition, I may specially mention 

 the fermentation of milk and other dairy products ; the 

 enzymes, and the conditions of yeast nutriment. As regards 

 the technical part of the work, a new section deals with methods 

 of cleansing and disinfection in the fermentation industry, and 

 the section dealing with the application of pure cultures to 

 the various branches of the fermentation industry has been 

 considerably enlarged. In its present form the book will, I 

 hope, serve as a manual, not only to zymo-technologists, but 

 also to analysts and physiologists.* 



For convenience, the old names of yeast species have been 

 retained along with the new, in the systematic treatment 

 given in the fifth chapter. 



As the work is concerned with the micro-organisms of the 

 fermentation industry, due regard has been paid to the practical 

 application of research work, and the description of both 

 useful and injurious species has received special attention. 

 The classification of the yeasts has been partially based on 

 the same requirements. The description of each species em- 

 phasises those characteristics that are of special importance 

 to the industry. 



I am glad to take the opportunity of expressing my thanks 

 to the head of the students' department in my laboratory, 

 Herr J. C. Holm ; the systematic part of Chap, v., together 

 with the very full bibliography, are essentially his work. 



Finally, I wish to express my warm thanks to many authors 

 who have kindly sent me reprints of their published works. 

 I regret that the limited extent of my book has in many 

 cases prevented me from making use of valuable publications. 



COPENHAGEN, January, 1909. ALFRED JORGENSEN. 



* A short description of ths most important practical conditions found in 

 the fermentation industry and in the laboratory is to be found in my short work, 

 Practical Management of Pure Yeast. London, 1903. 



