Page:The yeasts (1920).djvu/9

 FOREWORD

O class of microorganisms 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 Egyptian mummies, it is known that these people were familiar with yeast fermentations, although they probably did not have explanations 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. Today 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 deficiency 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, were 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 Guilliermond. The investigations of this authority make the book especially valuable. These facts made it seem advisable to translate the volume for publication in the English language in order that the data might be available to the practitioners and students who do not read