Maybe Sharper Image sells one of these :
Santorio Sanctorius, the 17th-century Paduan physician and father of quantitative medicine, spent the better part of thirty years eating, sleeping, working, and making love in a specially constructed “statical chair” that was attached through his ceiling to the arm of a finely calibrated balance. His scientific mission: to precisely weigh all of the food and liquid he consumed as well as the “sensible discharges” excreted by his body. Subtracting one from the other, he was able to calculate his “insensible perspiration,” the weight lost through the pores and during respiration. By taking measurements while fasting, Sanctorius determined that the average invisible excretion over the course of a day was 1.25kg — greater than the total loss through the more malodorous visible excretions. This ingenious experiment layed the foundation for the science of metabolism and the proud tradition of scientific self-experimentation.