Geophagia in response to stress and arthritis.

Geophagia, the consumption of nonnutritive dirt, has previously been shown to be increased when rats have been made acutely ill. The present paper reports two experiments in which geophagia in response to stress and arthritis was measured. In the first experiment, experimental rats were injected with Freund's Complete Adjuvant (FCA), a mineral oil suspension of killed Mycobacterium butyricum. They ate significantly more kaolin (a nonnutritive substance) than controls, suggesting that geophagia is a behavioral measure of illness. In a second study, kaolin consumption was similarly elevated in stressed and/or arthritic animals as well as in control rats living in the same room. Nonstressed controls housed in a remote room ate significantly less kaolin than rats in all other groups. It was concluded that geophagia may occur in response to any homeostatic alteration (stress state). Furthermore, this state can presumably be communicated to naive rats from adjacently-housed stressed animals. Geophagia was postulated to occur in animals who experience a generalized stress reponse since this state may involve gastro-intestinal malaise.