It is not an easy task to prepare a revision of a book in a rapidly growing field. The preparation of this third edition has taken many long hours. But there have been compensations, for now and again as I have searched through the many journals that record the efforts of a host of workers, isolated bits of information have seemed to fit into a pattern which has helped to give more meaning to our broad understanding of the living substance and its mechanism. Indeed, at times, I have felt like a man working on a jigsaw puzzle. At first the separate pieces of the puzzle seem to bear little relation to each other, but after a while, one or two pieces fit together and then gradually occasional others fall into place and this makes further progress possible, so that the assembled pieces take shape and have meaning.
The puzzle that faces the general physiologist is perhaps the most difficult of all those that face the inquiring human mind, for in the small compass of a living cell are marvelous intricacies of mechanism. Certainly at the present time there is nothing like a complete understanding of this mechanism. However, in the past decade much has been learned and the knowledge that has been gained gives us new insight which will help in the solution of problems of importance both on the theoretical and on the practical side. If we could know why muscles contract, why cells divide, and why impulses pass along nerves, if we could know why living material behaves as it does when exposed to one chemical or another, we would have information which would help in the understanding of human ailments and human shortcomings.
In the attempt to solve physiological problems, the general physiologist has the great advantage of being able to attack these problems in the simplest and most rewarding material. More and more we have come to appreciate the amazing similarity of all forms of life. What is true for the protoplasm of an ameba is often true for the protoplasm of man. Little by little our understanding is growing. From our knowledge of the simpler types of living substance we can attempt to interpret more complex types. Such interpretation has been of great value in the immediate past and beyond doubt will be of even greater value in the years to come. Indeed the future of the science of general physiology has never looked brighter. It is my hope that this book will be of help both to those who approach the subject for the first time and those who are experienced workers in the field. The beginner will . . .