which means to chew the cud. first described in ancient times, and mentioned in the writings of aristotle, rumination syndrome was clinically documented in 1618 by italian anatomist fabricus ab aquapendente, who wrote of the symptoms in a patient of his. among the earliest cases of rumination was that of a physician in the nineteenth century, charles-édouard brown-séquard, who acquired the condition as the result of experiments upon himself. as a way of evaluating and testing the acid response of the stomach to various foods, the doctor would swallow sponges tied to a string, then intentionally regurgitate them to analyze the contents. as a result of these experiments, the doctor eventually regurgitated his meals habitually by reflex. numerous case reports exist from before the twentieth century, but were influenced greatly by the methods and thinking used in that time. by the early twentieth century, it was becoming increasingly evident that rumination presented itself in a variety of ways in response to a variety of conditions. although still considered a disorder of infancy and cognitive disability at that time, the difference in presentation between infants and adults was well established. studies of rumination in otherwise healthy adults became decreasingly rare starting in the 1900s, and the majority of published reports analyzing the syndrome in mentally healthy patients appeared thereafter. at first, adult rumination was described and treated as a benign condition. it is now described as otherwise. while the base of patients to examine has gradually increased as more and more people come forward with their symptoms, awareness of the condition by the medical community and the general public is still limited. in other animals the chewing of cud by animals such as cows, goats, and giraffes is considered normal behavior. these animals are known as ruminants. such behavior, though termed rumination, is not related to human rumination syndrome, but is ordinary. involuntary rumination, similar to what is seen in humans, has been described in gorillas and other primates. macropods such as kangaroos also regurgitate, re-masticate, and re-swallow food, but these behaviors are not essential to their normal digestive process, are not observed as predictably as the ruminants', and hence were termed "merycism" in contrast with "true rumination".