Lead has been known to attack the central nervous system in such a way as to produce an intellectual apathy and muscular weakness somewhat resembling the early stage of the demented form of general paralysis, but without its ataxic symptoms and its regular progress. The presence of lead in the urine, and the marked improvement from the use of {199} iodide of potassium, tonics, and electricity, are sufficient to establish the diagnosis. Chronic and persistent alcoholism is always attended with some mental impairment, which may so resemble the dementia of general paralysis, with marked moral perversion, mental exaltation, grand delusions, muscular tremor, ataxic symptoms, and impaired muscular power, as to make the diagnosis doubtful for several months, until removal of the cause (alcohol) in the course of time causes the symptoms to so abate as to make the real character of the disease evident. I have once seen chronic interstitial nephritis without its usual prominent symptoms and with mild uræmic convulsions mistaken for general paralysis. A tumor of the brain, if not attended with the common symptom of vomiting, may be the cause of convulsions and headache resembling those often seen in general paralysis. Optic neuritis or atrophy is usual in cerebral tumor, but rare in a stage of general paralysis so early that the diagnosis might be doubtful. Hemorrhagic pachymeningitis also now and then simulates an obscure case of general paralysis in the early stage, but a few weeks at most settle any doubts in the matter. Although diffuse cerebral syphilis is more apt to be associated with distinctly localized symptoms than the demented form of general paralysis, and although it is characterized by a mental apathy and physical torpor which follow a more regular course with more definite symptoms, resulting in a slow decay, yet there may be doubtful cases in which the differential diagnosis is impossible, and in which antisyphilitic treatment does not throw any light on the subject. Syphilitic new growths, endarteritis, and meningitis may so far improve from the use of mercury or the iodide of potassium as to end in an apparent cure, but in those cases the symptoms are not so marked as to make an exact diagnosis always possible. A distinct syphilitic cachexia is presumptive evidence of syphilitic encephalitis when there is doubt whether the syphilis is the cause or the diathesis. Profound melancholia is not so often as varying gloom or moderate despondency a symptom of general paralysis. When it is such, there are developed in time the other marks of that disease, and it will only be necessary to hold the diagnosis in reserve for their appearance. The melancholia masks the dementia unless it is very carefully sought for, and the tremor may be as marked in melancholia as in the early stage of general paralysis, but more universal.