3 io THE POPULAR SCIENCE MONTHLY. 



ally 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 dis- 

 tinctly 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 fol- 

 lows 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 limit- 

 ed 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 min- 

 isters to the lost function ; and that the sudden recovery which some- 

 times 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 re- 

 stored, 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 acquire- 

 ments. 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 



