He was probably in the same mess as the Medical Assistants,or Sick Berth Attendants as they were called when I joined (1964). One of these would have been a DSA,or Dental Surgery Attendant,whose job it was to give injections of anaesthetic to dental patients,and known colloquially as "The Number".Of course ,the loss of such a person would have painful consequences for future dental attendees,thus it was no joke to "Lose the Number" of your mess.