Temple, J. G.: Animal Magnetism: Using magnetic stir bars to learn about digestive passage rate in snakes.

Snakes, as classic ectotherms, are interesting subjects for studying the relationship between temperature and physiological processes. They are particularly well-suited for studying digestive passage rate given the linear anatomical arrangement of their digestive tracts. In this paper, a simple and inexpensive laboratory exercise in which your students can design and carry out an experiment to track the passage of an ingested meal through the digestive system of the garter snake (Genus Thamnophis) is described. Teflon-coated micro stir bars are placed in a meal and their location in the snake is determined using a standard compass. Using the guided inquiry approach, the students are provided background information on the topic and the experimental techniques, and they are then allowed to develop their own hypotheses and design their own experiments with guidance from the instructor. The digestive passage rate is determined over a range of temperatures, and the direct relationship between temperature and digestive passage rate can be easily demonstrated using relatively small sample sizes. This exercise is effective for discussions of comparative physiology and anatomy in vertebrates. The straightforward technique can be easily modified to fit the needs of courses with all levels of students.