Early on in the movie Dr. Brooks (Sidney Poitier) enters the Doctors Room to change to get his whites on. It's clear that he actually never zips up the zipper of his pants.
After Dr. Brooks retrieves the spinal tap tray from the cabinet and heads back to the ward where Ray and John Biddle are being treated, the shadow of the boom microphone can be briefly seen on the wall upper left on the screen.
The Deputy asks Dr. Brooks if he's going to need any instruments, and he replies, "You keep them locked up." The deputy's answer is, "This ain't no maternity ward, doc" implies they can be used by any criminal as weapon against the staff. However, they are not locked in a secure cabinet in a nondescript room; they're locked in cases with glass doors that line the hallway of the ward - cases that could easily be smashed, giving access to instruments that could be used as weapons.