Donald C. Jackson's "Life in a Shell"

Donald C. Jackson is Professor Emeritus of Medical Science, Brown University.

He applied the “Page 99 Test” to his new book, Life in a Shell: A Physiologist’s View of a Turtle, and reported the following:

My book Life in a Shell describes studies that I and others have conducted on turtles and is written in a personal style that tries to give the flavor of biological research. Many aspects of the turtle’s physiology are covered including a striking adaptation for which turtles are particularly well-known. This is their capacity to survive for long periods without oxygen, a trait that helps species like painted turtles survive winter months in frozen ponds. Page 99 is within the chapter where I discuss this trait. On that page I am completing the description of an experiment that a graduate student and I conducted in which we had painted turtles submerged for 3 months in cold water near the freezing point without being able to breathe and with no oxygen in the water. This sounds inhumane, but turtles in the temperate zone of North America can experience this every winter. In the experiment described on page 99, we have connected a tube that had previously been surgically implanted in an artery of one of these turtles and were attempting to measure its heart rate and blood pressure with appropriate instumentation. Once everything was hooked up, we watched the pen on the polygraph but it was a flat line and stayed that way for several minutes. We (and now I quote from page 99)

were starting to fear that the turtle had no blood pressure when slowly, very slowly, the pen began to move upward. It reached its highest level and then even more slowly began to descend toward the baseline. The turtle’s heart had finally produced a beat. We continued to record the pressure, and sure enough additional beats continued to occur at long intervals, the longest interval between beats being an astounding ten minutes! In a human heart at rest, the interval between beats is normally one second or less.

The slow heart rate of the cold anoxic turtle is associated with an incredibly low metabolic rate that is one of the key reasons that explains its ability to survive without oxygen. The rest of the book discusses other physiological features of this remarkable animal, many of which are influenced by its iconic anatomical feature, its shell.

Learn more about Life in a Shell at the Harvard University Press website.

--Marshal Zeringue