Persin is a fungicidal toxin present in the avocado. It is generally harmless to humans, but when consumed by domestic animals in large quantities it is dangerous. Persin is an oil-soluble compound structurally similar to a fatty acid, and it leaches into the body of the fruit from the pits. Negative effects in humans seem to be primarily in allergic individuals. Animal studies show that exposure to persin leads to apoptosis in certain types of breast cancer cells. It has also been shown to enhance the cytotoxic effect of tamoxifen in vitro. Persin is however highly insoluble in aqueous solutions and more research will be needed to put it into a soluble tablet form. In birds (which are particularly sensitive to the avocado toxin), the symptoms are: increased heart rate, myocardial tissue damage, labored breathing, disordered plumage, unrest, weakness, and apathy.