A Guide to the World of the Yeasts J. F. T. Spencer and D. M. Spencert As the well-known authority on yeasts, the late Professor Rose, frequently pointed out, it is impossible for one person to present, in a single volume, the details of the life, composiotion, habitats, relationships, and actual and potential uses to man­ kind of the 500 (at last count) known species of yeasts. This book confirms the truth of this statement. However, our aim is actually more modest than that, and this book is an attempt to introduce the general reader, and possibly some interested specialists, to the lives of the yeasts in their natural and more artificial habitats, their use by human beings, and to give some idea of the wonderfully complex activities within the yeast cell, the characteristics of the metabolism and molecular biology of yeasts, and the applications of these characteristics to life in the present-dayworld ofhuman existence. The book proceeds from a brief chapter on what is and is not known of the origins and early history of the yeasts, through a description of their classification, relationships, habitats and general life style, their external morphology and internal structures and mechanisms within their cells, the regulatory mechanisms controlling processes such as signal transmis­ sion, mating, cell fusion, and many others.