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310 attributable to "embolism" of the middle meningeal artery, whereby the passage of blood through it is greatly impeded; this "embolism" consisting in the plugging of the artery by a fibrinous clot brought from the heart, where it has been produced by valvular disease. In the second of the cases just referred to, the usual brain-lesion having been found, and the middle meningeal artery having been examined, the fons et origo of the mischief was found to be, not "embolism," but a morbid deposit on the inner wall of the artery, producing a corresponding .obstruction to the circulation. Looking, then, to the fact that immediate cessation of Mental activity is distinctly and unmistakably produced by the entire suspension of Blood-circulation through the Brain, how can the Physiologist refuse to recognize, in this local reduction of the Circulation, the Physical cause of that limited reduction of Psychical activity which so distinctly follows it?

But further, this singular fact, taken in connection with the recent great extension of our knowledge as to the local alterations in the calibre of the Arteries, which are produced through the "Vaso-motor" system of Nerves, obviously points to the probability that the limited but transient lapses of Memory just alluded to are due to a local reduction of the blood-supply in the part of the Cerebrum which ministers to the lost function; and that the sudden recovery which sometimes occurs is the result of the renewal of the normal circulation, through the giving way of the impacted clot, or the yielding of the spasmodically-constricted arterial wall.

Thus Dr. Rush, of Philadelphia, was acquainted with a person of considerable attainments, who, on recovering from a fever, was found to have lost all his acquired knowledge. When his health was restored, he began to apply himself to the Latin Grammar; and, while, one day, making a strong effort to recollect a part of his lesson, the whole of his lost impressions suddenly returned to his remembrance,so that he found himself at once in possession of all his former acquirements.—The like sudden restoration, after an equally sudden loss, occurred in another case in which all acquired knowledge was lost for a whole year; and in both the loss and the recovery there was clear evidence of strong Emotional excitement, which is well known to the Physiologist to have a most powerful control over the calibre of the Blood-vessels.

There is another class of familiar phenomena, which affords strong evidence of the dependence of the recording process upon Nutritive changes in the Brain. Every one is aware that what is rapidly learned—that is, merely committed to Memory—is very commonly forgotten as quickly, "one set of ideas driving out another." That thorough apprehension of what is learned, on the other hand, by which it is made (as it were) part of the Mental fabric, is a much slower process. The difference between the two is expressed by the colloquial term