FOREWORD 



NO class of microoiganisms has been more intimately associated 

 with the progress and development of the human race than the 

 yeasts. Since the earliest times, these microorganisms have 

 been used to bring about changes which it would have been difficult to 

 have accomplished by other methods. Since microscopic examinations 

 have revealed the presence of yeast cells in bread found with Egyp- 

 tian mummies, it is known that these people were familiar with 

 yeast fermentations, although they probably did not have explana- 

 tions for the changes which were observed. The Norsemen prepared 

 an alcoholic drink from milk, as is done today by certain nomadic 

 races, the fermentation of which was, in part, caused by yeasts. To- 

 day we find the yeasts of ever-increasing interest and importance. 

 The food microbiologist must understand the physiology of these 

 organisms if he is to successfully cope with them. They are assuming 

 greater importance in medicine, especially in relation to certain de- 

 ficiency diseases, constipation, and skin infections. Great industries 

 have been established which rest entirely on the chemical changes 

 brought about by yeasts and their enzymes; some of them would be 

 developed with difficulty, we.re it necessary to use strictly chemical 

 methods. The compressed yeast industry itself has reached a high 

 state of development with its several factories located in different 

 parts of America and distributing agencies in practically all of the 

 cities and villages. Many industries have been greatly changed by 

 the availability of fresh, active yeast whenever it is needed. Despite 

 the facts that yeasts have always been of great significance to the 

 human race and that they will probably have greater significance in 

 the future, it remained for Guilliermond to collect the various data, 

 which have accumulated in regard to them, into one volume. Several 

 treatises have been prepared which deal with the yeasts in relation to 

 fermentations, but no real definitive treatise on the yeasts, as such, 

 has appeared which is comparable to the volume prepared by Guillier- 

 mond. The investigations of this authority make the book especially 

 valuable. These facts made it seem advisable to translate the vol- 

 ume for publication in the English language in order that the data 

 might be available to the practitioners and students who do not read 



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