CHAP. XI.J FUNCTIONS OF THE CEREBRAL CONVOLUTIONS. 365 



pable of a single mental nervous action, whether voluntary or 

 sensitive. 



When the membranes of the brain are in a state of inflammation, 

 disturbance of the mental faculties is an invariable accompaniment 

 to an extent proportional to the degree of cerebral irritation, and 

 more especially so when the inflammation is seated in the pia mater 

 of the convolutions. This disturbance of mind is frequently in- 

 dicated by the manifestation of delirium of a more or less violent 

 kind. It is plain that in such a case, the delirium arises from the 

 altered state of the circulation in the gray matter of the convolu- 

 tions, the blood-vessels of which are immediately derived from those 

 of the pia mater, so that the one cannot be affected without the 

 other likewise suffering. And it may be stated, as a fact no less 

 interesting in a physiological than important in a practical point of 

 view, that in many, if not in most, instances of violent delirium, 

 such, for example, as delirium tremens, the vesicular matter of the 

 convolutions is found after death to be bloodless, as if its wonted 

 supply of blood had been completely cut off from it. Thus it 

 happens in the delirium after great operations in that of rheu- 

 matic fever and perhaps also of gout and in that which occurs 

 in the more advanced stages of continued fever. 



We learn from the most trustworthy reports of the dissections of 

 the brains of lunatics, that there is invariably found more or less 

 disease of the vesicular surface, and of the pia mater and arachnoid 

 in connexion with it, denoted by opacity or thickening of the latter, 

 with altered colour or consistence of the former. 



From these premises it may be laid down as a just conclusion, that 

 the convolutions of the brain are the centre of intellectual action, or, 

 more strictly, that this centre consists in that vast sheet of vesi- 

 cular matter which crowns the convoluted surface of the hemi- 

 spheres. This surface is connected with the centres of volition and 

 sensation (corpora striata and optic thalami), and is capable at once 

 of being excited by, or of exciting them. Every idea of the mind 

 is associated with a corresponding change in some part or parts of 

 this vesicular surface ; and, as local changes of nutrition in the ex- 

 pansions of the nerves of pure sense may give rise to subjective sen- 

 sations of vision or hearing, so derangements of nutrition in the 

 vesicular matter of this surface may occasion analogous phenomena 

 of thought, the rapid development of ideas, which, being ill-regu- 

 lated or not at all directed by the will, assume the form of delirious 

 raving. 



The actions of the convoluted surface of the brain, and of the 



