“Are you an Alienist?” (47)

An alienist is another term for a mental pathologist or psychiatrist – that is, one who is capable of determining the mental fitness (“saneness”) of an individual. Alienists are often called upon in courts of law when an insanity plea is entered, to verify or negate this claim. It is logical that in Conrad's novella such an individual would also be called upon to identify any possibility of incompetence to participate in the voyage to the Congo; a business owner would not want to send an employee on such a mission only to find them mentally unable by virtue of insanity to complete their assigned duties.

Source:

"Alienist - Definition from Merriam-Webster's Medical Dictionary." Dictionary and Thesaurus - Merriam-Webster Online. Web. 24 Aug. 2009.

http://www.merriam-webster.com/medical/alienist.