THE NEBVOUS SYSTEM. 101 



first very simple, and their sensations do not seem very 

 distinct. In the earth-worm, a knotted cord extends through- 

 out the whole length of the body, and to and from these 

 knots or ganglions the nerves proceed; but each of these 

 parts seems equal to every other, and there is no special- 

 ization of any. This simplicity of structure gives way to a 

 form more complex as we ascend in the animal scale. 



196. Functions of the Nerves. All parts of the body 

 are not equally supplied with nerves, and there are parts 

 which seem to have none. Hence, no doubt, is the fact that 

 whilst some parts are extremely sensitive, others are but little 

 so, or wholly insensible. No experiments are required to show 

 that a part owes its sensibility to the contiguity of the nerve 

 which connects it with the central organs of the nervous 

 system. The nerves, then, are not the organs by which the 

 sensations are perceived ; they merely transmit them to the 

 central system, where all perception resides.* 



197. Where, then, is the seat of the faculty of perception ? 

 Which is the perceiving organ ? 



198, Influence of the Encephalon. Does perception 

 reside in the spinal marrow, the cerebellum, or the cerebrum ? 

 Experiments on living animals, surgical operations, and 

 accidents, have repeatedly proved that the seat of perception is 

 not in the spinal marrow. The cutting this across in a living 

 animal merely destroys the sensibility, and paralyzes the 

 movements of all the parts supplied with nerves from it below 

 the point divided. 



With the brain it is quite otherwise. The surface of 

 the brain and its substance generally, may be cut or irritated 

 in a living animal without it being sensible of any injury 

 or pain ; but remove it, and the whole body of the animal 

 instantly becomes insensible. The action of the brain is as 

 essential in the perception of sensations as for the acts of 

 volition. 



199. The insensibility of the brain when cut or rudely 

 touched is a remarkable circumstance, long known however 

 to surgeons. But the faculty of perceiving sensations caused 

 by impressions on the organs, resides in it ; and it would 

 seem, from Flourens's experiments, to reside more especially 



* It is now certain that perceptions or impressions on the central organs of 

 the nervous system are of two kinds ; one attended with consciousness, the 

 other without. R. K. 



