Excellent detail about this hierarchy is given in the founding documents, or typika, of hospitals. On top of the doctors is the lecturer; This teacher's duties were to educate the next generations of doctors in medicine. This made hospitals learning centers for humoral medicine and became a significant source of medical professionals. The faculty trained doctors in much the same way that modern medical schools train theirs: starting with theory, followed by observation, and finally introducing them into practice. Today we call recent medical graduates interns, in the Byzantine Empire they were called perissoi or "extras". As their role as medical schools grew, xenons became important sources and repositories of medical treatises. Xenones occasionally hired scribes to bind or transcribe manuscripts—a prohibitively expensive process before the advent of the printing press. The fact that hospitals can afford to pay for this reveals that they are well-funded and therefore significant,