After studying for his Ph.D. in 1954 with Hebb at McGill University in Montreal, he began to work with patients who suffered from "phantom limb" pain — people who feel pain in an arm or leg that has been removed. He found that pain often has little survival value, and some pains are entirely out of proportion to the degree of tissue damage, sometimes continuing long after injured tissues have healed. While still a postdoctoral student, Melzack began collecting "pain words" and putting them into classes that belonged together, like "hot," "burning," "scalding," and "searing".