FUNCTIONS OF THE CEREBRUM. 363 



either a diminution or a total absence of this fluid. It appears from the ex- 

 periments of Magendie (to whom our knowledge of the importance of this 

 fluid is chiefly due), that its withdrawal in living animals causes great dis- 

 turbance of the cerebral functions, probably by allowing undue distention of 

 the blood-vessels ; it is, however, capable of being very rapidly regenerated ; 

 and its reproduction restores the nervous centres to their natural state. 



477. As the cerebro-spinal fluid can readily find its way from the sub- 

 arachnoid spaces of the cranial cavity into those of the spinal, and as the 

 latter are distensible, to a very considerable extent, it evidently serves as an 

 equalizer of the amount of pressure within the cranial cavity ; admitting the 

 distention or contraction of the vessels to take place, within certain limits, 

 without any considerable change in the degree of compression to which the 

 nervous matter is subjected. That this uniformity is of the greatest import- 

 ance to the functional exercise of the brain, is evident from a few well-known 

 facts. If an aperture be made in the skull, and the protruding portion of the 

 brain be subjected to pressure, the immediate suspension of the activity of 

 the whole organ is the result ; in this manner, a state resembling profound 

 sleep can be induced in a moment; and the normal activity is renewed as 

 momentarily, as soon as the pressure is withdrawn. This phenomenon has 

 often been observed in the Human subject, in cases in which a portion of the 

 cranial envelope has been lost by disease or injury. The various symptoms 

 of Cerebral disturbance, which are due to a state of general Plethora, are 

 evidently owing to an excess of pressure within the vessels ; but an undue 

 diminution of pressure is no less injurious, as appears from the disturbance in 

 the Cerebral functions, which results from the very opposite cause, namely, 

 a depression of the power of the heart, or a deficiency of blood in the ves- 

 sels. It is of peculiar importance to bear in mind the disturbance of the 

 Cerebral functions, which is occasioned by internal pressure, when we are 

 endeavouring to draw inferences from the phenomena presented by disease. 



478. We shall now proceed with our Physiological inquiry into the func- 

 tions of the Cerebrum ; confining ourselves, in the present Section, to certain 

 general positions, with regard to which most Physiologists are agreed ; and 

 referring to the Appendix for a notice of the more detailed system of Cerebral 

 Physiology, first propounded by Dr. Gall. We shall, as before, apply to 

 Comparative Anatomy, to Experiment, and to Pathology, for our chief data. 

 Any general inferences, founded only upon observation of the phenomena pre- 

 sented by Man, must be looked upon with suspicion; since every advance in 

 Comparative Physiology leads us to perceive, how close is the functional rela- 

 tion between organs, that are really of analogous nature in different classes of 

 animals ; and how necessary, therefore, it is, to examine and contrast all the 

 facts which we can attain in regard to them, in order to impart to our con- 

 clusions the utmost validity of which they are capable. Our first general 

 proposition is, that the Cerebrum is the sole instrument of intelligence; by 

 which term is implied the intentional adaptation of means to ends, in a man- 

 ner implying a perception of the nature of both. The actions performed by 

 the lower animals are often such, as to leave us in doubt, whether they are 

 the result of a mere Instinctive impulse, or of an Intelligent adaptation of 

 means to ends ; and we are guided in our determinations, chiefly by the uni- 

 formity of these actions, in the several individuals of the same species. If 

 we analyze any of our own instinctive actions, we shall perceive the same 

 absence of design on our own parts, as that which we attribute to the lower 

 animals. No one would assert that the tendency to sexual intercourse is the 

 result of a knowledge of its consequences, and of a voluntary adaptation of 

 means to ends ; or that, if we can imagine a man newly coming into the 



