PEEFACE TO THE THIKD EDITION. 



A GREAT portion of this edition has been entirely re-written 

 and considerably enlarged. Among its new features, I may 

 mention a biological treatment, performed in my laboratory, 

 of several English high-fermentation yeasts, isolated from 

 yeast used in breweries and distilleries in various parts 

 of Great Britain, and a summary of observations, made 

 in my laboratory in the course of years, on the vari- 

 ations which yeast undergoes during its use in factories', 

 further, descriptions of some particularly interesting yeast 

 species discovered in recent years ; and, finally, a concise 

 account of the organisms occurring in milk, and of the 

 use of pure cultures of lactic acid bacteria in dairies and 

 distilleries. 



These enlargements have necessitated the insertion of a 

 considerable number of new figures. 



Mr. S. H. Davies, M.Sc., has kindly revised, linguistically, 

 all the new sections inserted in this edition. I therefore 

 tender him my hearty thanks. 



ALFRED JORGENSEN. 



COPENHAGEN, July, 1898. 



