Who in the rainbow can draw the line where the violet tint ends and the orange tint begins? Distinctly we see the difference of the colors, but where exactly does the one first blendingly enter into the other? So with sanity and insanity. In pronounced cases there is no question about them. But in some supposed cases, in various degrees supposedly less pronounced, to draw the exact line of demarcation few will undertake tho' for a fee some professional experts will. There is nothing nameable but that some men will undertake to do it for pay.

Ch. 21 - Billy Budd, the Sailor (1891)