I think it is a little unfair for DOCTOR to mean DS... Is there such a thing as a Doctor of Surgery? Don't doctors become Misters when they qualify as surgeons?
I took "Goes on kidney machine" to be short for "[He who] goes on kidney machine...", ie a dialyser. I would never have got manatees.
This was one tough puzzle!
Thank you both, kayakamina and amtaff, for clearing up some confusion I had.