Foreword - Prof Lewis Wolpert

A central issue in developmental biology is how genes control the behaviour of cells in the embryo so that reliable functional organs, like kidneys and brains, develop. While there has been good progress in understanding the early specification of the cells in such organs much still needs to be learned about their later development and growth. Indeed, growth control of the fetus is of particular importance as there is evidence that failure of the human fetus to grow properly can lead to both cardio-vascular disease and diabetes in later life.

Studying the growth of organs like the kidney, brain and pancreas - and indeed other organs - presents a special problem as they are made up of a very large number of functional units. In the case of the kidney one needs to know both the number and size of glomeruli, while in the brain it is often necessary to count the number of a particular class of neuron or synaptic connections. However, with almost all pertinent studies, it is not possible to count the number of relevant units directly. Yet the information is essential if we want to know how changes in genetic constitution of an animal affect the organ's development. For example, what effect does the absence of a particular growth factor or reduced nutrition have on the number or size of glomeruli in the kidney, and at what stage of development does this occur? Has behavioural experience or environmental insult affected the number of neurons in a particular brain structure such as the amygdala?

The only reliable way to obtain such information is by means of stereology. Stereology is an absolutely essential tool for any biologist who needs to know the number of units in any system - whether they be functional units like glomeruli or cell organelles like mitochondria. It also provides a means of obtaining both the size and surface area of the objects under consideration. Stereology is a technique that enables one to obtain data on the number of identifiable objects in a three-dimensional structure by sampling in two dimensions. That is, it provides a technique for counting the objects on a slice from the structure such as a histological specimen viewed under the microscope. It has the enormous virtue of having a rigorous mathematical foundation and rules for counting that also give a reliable measure as well as an indication of the precision. It is inexpensive and, once learned, easy to use.

Stereology has all too often been neglected, so this book provides the necessary information for all biologists interested in numbers of objects in a structure. It is thus invaluable for both developmental biologists and toxicologists. The book not only provides a detailed description of stereology and how to use it but also includes exercises, attempts at solutions of which could even be entertaining. They will certainly be rewarding.

Lewis Wolpert 1997

Lewis Wolpert is Emeritus Professor of Biology as Applied to Medicine in the Department of Anatomy and Developmental Biology of University College, London. His research interests are in the mechanisms involved in the development of the embryo. He was originally trained as a civil engineer in South Africa but changed to research in cell biology at King's College, London in 1955. He was made a Fellow of the Royal Society in 1980 and awarded the CBE in 1990. He was made a Fellow of the Royal Society of Literature in 1999.