The enzyme, ß-glucuronidase, present in mammalian tissues, catalyses the breakdown of ß-d-glucuronides in vitro to glucuronic acid and the corresponding "aglucone ". Although evidence for its presence was obtained by Roehmann in 1906 and by Sera in 1911ß., it was not till fairly recently that this enzyme was studied in any detail. At one end of the scale in the animal species there are the carnivores with a comparatively simple alimentary tract. At the other end come the herbivores with a much more elaborate digestive apparatus. The omnivores occupy an intermediate position in this respect.