The chemical caused lab rats to lose weight. When pregnant rats were exposed to it, their pups lost weight, too, and their pups’ skulls, ribs, and pelvises tended to develop abnormally. The compound, referred to by the number “647-42-7” in Environmental Protection Agency records, also caused discoloration of the teeth, increased liver weights, decreased how much their infants nursed,and lowered the animals’ red blood cell counts.