Book excerpt: Physical Techniques in Biological Research, Volume IV: Special Methods presents the methods of determining body fluid volume. This book is composed of six chapters that discuss the techniques of vascular perfusion and evaluate the nature of the electrode reaction. It also demonstrates the certain characteristics of the oxygen cathode. Some of the topics covered in the book are the methods for pressure measurement; techniques in gas volume measurement; modes of gas flow measurement; applications of pressure, volume, and flow measurements; and procedures for gas analysis. Other chapters deal with the contents of perfusion media, the determination of extracellular fluid volume, and an analysis of the components of perfusion apparatus. Applications of ultrasonic fields to the study and alterations of biological systems are presented. The last chapter is devoted to the developments made in the use of flame photometry and its description. The book can provide useful information to doctors, students, and researchers.