The case of Nicolai has unquestionably been that of many whose love of science has not been able to overcome their natural reluctance to communicate to the public the particulars attending the visitation of a disease so peculiar. That such illnesses have been experienced, and have ended fatally, there can be no doubt; though it is by no means to be inferred, that the symptom of importance to our present discussion has, on all occasions, been produced from the same identical cause. Dr. Hibbert, who has most ingeniously, as well as philosophically, handled this subject, has treated it also in a medical point of view, with science to which we make no pretence, and a precision of detail to which our superficial investigation affords us no room for extending ourselves. The visitation of spectral phenomena is described by this learned gentleman as incidental to sundry complaints; and he mentions, in particular, that the symptom occurs not only in plethora, as in the case of the learned Prussian we have just mentioned, but is a frequent hectic symptom--often an associate of febrile and inflammatory disorders--frequently accompanying inflammation of the brain--a concomitant also of highly excited nervous irritability--equally connected with hypochondria--and finally united in some cases with gout, and in others with the effects of excitation produced by several gases. In all these cases there seems to be a morbid degree of sensibility, with which this symptom is ready to ally itself, and which, though inaccurate as a medical definition, may be held sufficiently descriptive of one character of the various kinds of disorder with which this painful symptom may be found allied.