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 AUTHOR'S PREFACE

SINCE the celebrated memoir by Pasteur on alcoholic fermentation, the yeasts have never ceased to assume an ever-increasing importance in agriculture and the industries. The classic investigations by Pasteur, followed by those of Hansen, have shown the profit that may result from a methodical study of the various species of yeasts, by a knowledge of the conditions necessary for their development and biochemical characteristics for application to the fermentation industries. No one may overlook the benefits which came to such industries by the use of pure cultures and selected species, and the avoidance of yeasts which caused defects in fermented products. The fermentologists have also benefited greatly by these methods. Finally, the relatively recent investigations have shown the relationship of yeasts to certain diseases in man and animals.

From a purely theoretical point of view the yeasts, on account of the facility with which they allow themselves to be cultivated in artificial media, and by the relatively large size of their cells, are especially favorable objects for experimentation upon which very important investigations of physiology, cytology and sexuality have been made. They have contributed appreciably to the progress of general physiology and biology.

It seemed useful to me to collect into one book all of the knowledge required on the morphology, physiology and taxonomy group of fungi, and to arrange it in such a manner that the data would be available for biologists, practitioners in industrial work, agriculturalists and physicians. That is what I attempted to accomplish in the little volume published in the Encyclopédie Scientifique under the editorial supervision of Dr. Toulouse.

Professor Tanner, of the University of Illinois, undertook the translation of this book into the English language in order to render it more accessible to American students and American investigators. This is indeed a great honor to me, one which I did not dream of when I prepared this modest work a few years ago. I am very happy to have this indication of friendship between scientific America and France, a friendship which I hope may become stronger and stronger. One sufficiently understands the significance of a scientific alliance of