In this small book I have tried to confine myself to the absolute necessities in a field which requires a knowledge of both biology and physics. It is meant as a primer for biological undergraduates. I hope it will lead some of them to further, more advanced, study. It has not been easy to present the subject in so few pages, and I am aware of many omissions. I hope readers will agree that it is best to concentrate on a small number of topics, which...