Some psychiatrists attribute great importance to the neuro-insane diathesis as a factor in the causation of insanity, whilst others belittle its influence. The term is misleading, for it suggests that this diathesis is confined solely to the mentally afflicted, and, further, its precise meaning is vague. A person is generally accused of possessing the neuro-insane diathesis if he presents a temperament which appreciably diverges from the mean of the sanguine and of the phlegmatic; if his actions are unduly strenuous or torpid, his expressions unwarrantably enthusiastic or lukewarm, his moods very variable or religiously constant; in brief, the neuro-insane diathesis may be resolved into a tendency to psychic or motor reaction disproportionate to the exciting stimulus. In common speech the person is emotional. But every person who is emotional is not an incipient lunatic. The faculty of conceiving undue enthusiasm, of persevering unfalteringly in ambition, in order to attain the acme of success in any sphere of life, demands an emotional power in excess of the normal. It is ridiculous thus to brand the best men of all nations as possessors of the neuro-insane diathesis. The term, with its plausible air of scientific accusation, is misleading and vague, and should be wholly discarded. All that psychiatrists wish to convey by it may be more accurately and more descriptively called the emotional diathesis.