Psychopaths Then and Now

 The other day I came across a curious case of how words change their meanings over (quite a short) time. Reading Willa Cather's 1922 novel One of Ours (of which, probably, more in due course), I found this passage, in which the protagonist Claude Wheeler, with the US army in France, asks a hospital doctor about a curious young man who has caught his attention. 'Oh yes!' says the doctor. 'He's a star patient here, a psychopathic case.' This is a young man who has lost his left arm in action and suffered some brain damage. Rather than be shipped home, he has elected to stay behind and make himself useful at the hospital – nothing remotely psychopathic about that... Then it gets stranger still, as the doctor continues, 'This psychopath, Phillips, takes a great interest in him and keeps him here to observe him.' At this point the penny drops: a 'psychopathic' case is a case in psychopathology, what we would now call psychiatry; and 'psychopath' is here simply short for psychopathist, i.e. psychiatrist. 
'Psychiatry' and 'psychopathy' (in the general sense of mental illness) seem to have come into the language at much the same time: the OED gives a date of 1846 for the first, 1847 for the second. Presumably they coexisted well into the 20th century, sowing confusion for the modern reader.