Introduction to the Dunham Lectures at the Harvard Medical School, 1928-29.[long dash]The author presents a new theory to explain coordinated action of the nervous system. It is based on his earlier theory that conduction between 2 anatomical units is possible only when they are "isochrone", that is, when the chronaxies are equal or at least within a ratio of 1 to 2. On the basis of experiments indicating changes in the chronaxie of a nerve or nerve center as a result of peripheral stimulation, the author suggests that the constitutional chronaxie of a tissue is subject to modification, through nervous influences, and suggests that coordination in the nervous system depends upon appropriate modifications of chronaxie, and the consequent opening and closing of nervous pathways.