This volume is a revised and enlarged version of Chapter 3 of. a book
with the same title, published in Romanian in 1968. The revision
resulted in a new book which has been divided into two of the large
amount of new material. The whole book parts because is intended to
introduce mathematicians and biologists with a strong mathematical
background to the study of stochastic processes and their applications
in biological sciences. It is meant to serve both as a textbook and a
survey of recent developments. Biology studies complex situations and
therefore needs skilful methods of abstraction. Stochastic models, being
both vigorous in their specification and flexible in their manipulation,
are the most suitable tools for studying such situations. This
circumstance deter- mined the writing of this volume which represents a
comprehensive cross section of modern biological problems on the theory
of stochastic processes. Because of the way some specific problems have
been treat- ed, this volume may also be useful to research scientists in
any other field of science, interested in the possibilities and results
of stochastic modelling. To understand the material presented, the
reader needs to be acquainted with probability theory, as given in a
sound introductory course, and be capable of abstraction.