Probably the most obvious characteristic of animals and people is that they are always doing something. We, for instance, work, think, read, and move around as long as we live. Even when we seem to do nothing at all, our hearts beat, and we breathe, think, and see. These things happen because our nerves and muscles work every moment of every day.
If you have ever stopped to ask what laws govern these never-ending activities of animals and men, you are in good company; intelligent people have wondered for centuries how the brain and muscles manage to work together to produce behavior. What are the biological laws that operate when one of us sees objects, hears sounds, gets hungry, or makes muscles work to move his body from one place to another? In the old days people figured it would forever be impossible to discover these laws; they believed that what went on in living things was too complex for mere mortals to understand. By now, however, the idea that the special rules operating for nerves and muscles are simple variants of the well-known laws all matter obeys has taken firm root. How this idea grew out of physical and chemical measurements on living tissue is to be the main topic of this book.
To anyone with plain common sense most biological