Having recently had some cases of myxoedema under my care I have had an opportunity of making the following analysis of their mental state. These patients are commonly sent to asylums as cases of dementia or melancholia. They present, however, few of the characteristics of either condition. Their memory for remote events is generally good and their impairment of memory for recent ones is slight and confined to a period coincident with the duration of their disorder. Their apprehension is fair, their coherence of thought is good, their reasoning power is sound, and their consciousness is clear. What depression they exhibit arises rather from a consciousness of their condition than from any more fundamental affection of the emotions... I submit then that the changes in the mental condition of those suffering from myxoedema are almost confined to the sphere of action. It seems necessary to suppose that either some toxin in the plasma surrounding the motor cells inhibits the chemical processes which originate a motor impulse or that the absence of some substance from the blood interferes with the discharge. This toxin is neutralised or this essential substance is supplied by the administration of thyroid extract; the patients get well and keep so as long as they continue to take thyroid. I have observed that the simultaneous exhibition of syrupus ferri iodidi appears to assist its action. We see this class of patients described by such terms as dull, listless, apathetic, taking a long time to comprehend and to answer questions, of sluggish ideation, of sluggish mentation, demented, depressed, moping, lethargic, suspicious, of impaired memory, sleepy, torpid, contented, and irritable. I suggest that this proves on careful inquiry to be but part of the truth and that the majority of these cases are sent to an asylum in error and could be as well treated outside one.