ACCOMPLISHED IN THE ENCEPHALON. 113 



tissue or organ by the amount of nervous supply, which his research 

 discloses. It may well be doubted, however, whether such sensibility 

 be by any means in proportion to the number of nerves received by 

 a part. Nay, some parts are acutely sensible in disease into which 

 nerves cannot be traced. To explain these cases, Reil 1 supposed that 

 each nerve is surrounded at its termination by a nervous atmosphere, 

 by which its action is extended beyond the part in which it is seated. 

 This opinion is a mere creation of the imagination. We have no evi- 

 dence of any such atmosphere ; and it is more philosophical to presume, 

 that the reason we do not discover nerves may be owing to the imper- 

 fection of our vision. 



We may conclude, that the action of impression occurs in the nerves 

 of the part to which the sensation is referred. As to the mode in 

 which this impression affects them we are ignorant. Microscopic ex- 

 amination of the nerves connected with sensory organs would seem to 

 show, that they come into relation with a 

 substance very analogous to the gray mat- Fig- 33 - 



ter of the encephalon, although its elements 

 are somewhat differently arranged. The 

 nervous fibres, too, appear to terminate in 

 close approximation with a vascular plexus ; 

 and a granular structure is present, which 

 as in the cortical portion of the brain 

 seems to be intermediate. This point has 

 been regarded as the origin of the afferent 

 fibres ; and as the seat of changes made by Distribution of Capillaries at the 



external impressions. 2 surface of the skin of the finger. 



The facts mentioned show, that the ac- 

 tion of perception takes place in the encephalon ; and that the nerve is 

 merely the conductor of the impression between the part impressed 

 and that organ. If a ligature be put round a nerve, sensation is lost 

 below the ligature ; but it is uninjured above it. If two ligatures be 

 applied, sensibility is lost in the portion included between the liga- 

 tures ; but it is restored if the upper ligature be removed. The spinal 

 marrow is sensible along the whole of its posterior column, but it also 

 acts only as a conductor of the impression. M. Flourens destroyed the 

 spinal cord from below, by slicing it away ; and found, that sensibility 

 was gradually extinguished in the parts corresponding to the destroyed 

 medulla, but that the parts above evidently continued to feel. Per- 

 ception, therefore, occurs in the encephalon ; and not in the whole, but 

 in some of its parts. Many physiologists Haller, Lorry, Rolando, and 

 Elourens 3 sliced away the brain, and found that the sensations continued 

 until the knife reached the level of the corpora quadrigemina ; and, again, 

 it has been found, that if the spinal cord be sliced away from below 

 upwards, the sensations persist until we reach the medulla oblongata. 



1 Exercitat. Anatom. Fascic., i. p. 28, and Archiv. fur die Physiologic, B. iii. 



9 Carpenter, Human Physiology, p. 85, Lond., 1842. 



3 Rolando, Saggio sopra la vera Struttura del Cervello, Sassari, 1809; and Flourens, Re- 

 cherches Experimental sur les Proprietes et les Fonctions du Systeme Nerveux, &c., 2de 

 edit., Paris, 1842. 

 VOL. I. 8 



