“Unlinked by a pacemaker, the cells beat irregularly, spasmodically, each tapping out a rhythm approximate to the 350 beats a minute normal to a chick. But as the observer watches, over a period of hours an astonishing phenomenon occurs. Instead of five independent heart cells contracting at their own pace, first two, then three, and then all the cells pulse in unison. There are no longer five beats, but one. How is this sense of rhythm communicated in the saline, and why?”