“The clicking resulting from adjustment can never be shown to be ‘that bone has been thrown in place,’ as they so strenuously maintain. “The sudden separation of the facets takes place, and the ‘clicking’ sound is produced. “Separating the facets of the two bones—that is the articular surfaces—and lets the air in and gives the sound.”
An early claim that cavitation does not indicate a successful adjustent. He even mentions "air" being let in.
