LECT. XIV. XV. CEREBRO-SPINAL SYSTEM. 255 



Characters of the Nervous Force. I shall commence by 

 briefly explaining the characters of the nervous force and 

 its laws, according to the present state of physiological 

 science. 



Cerebro-spinal System. All animals having a certain 

 degree of development, possess organs, by which they are 

 enabled to influence their muscles, and by the intervention 

 of which they perceive external actions. These organs 

 constitute the cerebro-spinal nervous system, which is prin- 

 cipally composed of an infinite number of ramifications, 

 disseminated throughout the body of the animal, and uniting 

 in a central mass, constituted by the brain and spinal 

 marrow. 



If we divide one of these ramifications in a living animal, 

 and afterwards touch, with either a red-hot iron or potash, 

 or wound with a needle, or pull with pincers, the portion 

 which remains in communication with the cerebro-spinal 

 axis, the animal manifests evident signs of pain ; but if we 

 apply these irritants below the section or ligature of the 

 nerve, no signs of pain are exhibited, and we perceive, 

 merely, contractions in the muscles to which the irritated 

 nerve is distributed. If we excite the uninjured nerve, 

 both pain and contraction simultaneously occur. Lastly, 

 if we tie the nerve in two places, and then irritate the part 

 included between the two ligatures, we produce neither 

 pain nor contraction. The nerve, then, has no other office 

 than that of transmitting and propagating the action of the 

 stimulant applied to it. This double action consists in a 

 sensation carried to the brain, and in a muscular contraction 

 communicated to the muscles. 



The physiologists, Bell, Magendie, Miiller, Pandyza, and 

 others, have discovered that there are some nerves which, 

 when excited, merely produce muscular contractions, and 

 others which, when submitted to the like irritation, only 



