All biological systems are regulated, that is, maintained at a level of performance necessary for homeostasis. Regulation implies existence of a controller such as the hypothalamus for temperature, the hypophysis for endocrine levels, brain centers for blood CO2 levels. Reviews of these and many other such systems comprise this book, with contributions primarily from associates of the University of Pennsylvania.
Some biological controls and regulations are exceedingly intricate and puzzling. Concepts and principles common to control engineers have recently helped to solve some of these puzzles. The concept of "set point," for example, explains how the hypothalamus can control temperature efficiently and yet permit fever and diurnal variations, a process which Hammel and Hardy cover in two stimulating chapters. The concept of "negative feedback" can explain why injections of cortisone depress the adrenal cortex and hypophysis, a system discussed by Smith and McCann. Study of engineering control "loops" can