Exorcism
In Catholic Christianity, exorcisms are performed in the name of Jesus Christ. A distinction is made between a formal exorcism, which can only be conducted by a priest during a baptism or with the permission of a bishop, and "prayers of deliverance" which can be said by anyone.
The Catholic rite for a formal exorcism, called a "Major Exorcism", is given in Section 11 of the Rituale Romanum. The Ritual lists guidelines for conducting an exorcism, and for determining when a formal exorcism is required. Priests are instructed to carefully determine that the nature of the affliction is not actually a psychological or physical illness before proceeding.
Lewis Ashmore
Ashmore was a noted exorcist having performed hundreds of exorcisms since the 1950s. "For decades Rev. Lewis Ashmore cast out devils during tent revivals in the Central Valley. People foamed at the mouth, talked back to him in a strange voice and writhed uncontrollably on the ground." Aged 75, two years before he died, Ashmore concluded that demonic possession could be explained in the 21st century by modern medicine. "Back in Christ’s day, these mental conditions weren’t yet diagnosed,” he said. “All exorcisms can be explained by psychology and science."