76 NERVOUS SYSTEM. 



24. That sensations may be perceived, it is necessary that the 

 nerves transmit them from the point where they are produced 

 to the brain, either directly, or through the intervention of the 

 spinal marrow. 



25. The brain is, at the same time, the seat of the WILL and of 

 the perception of sensations ; when, in consequence of a wound 

 or strong compression, this organ cannot perform its functions, 

 the animal becomes insensible, ceases to execute voluntary 

 motions and falls into a state resembling profound sleep. 



26. It is remarkable that the nerves which arise from the right 

 side of the spinal marrow communicate with the left hemisphere 

 of the cerebrum and vice versa ; this results from the crossing of 

 the fibres in the medulla nblongutn, and hence it is that when the 

 brain is paralysed on one side only, it is the members of the op- 

 posite side of the body which lose their sensibility and motion. 



27. Farther, the brain, although the seat of perception of sen- 

 sations, is itself very slightly sensible ; we may prick or cut it in 

 a living animal without causing pain. 



28. The spinal marrow is, on the contrary, extremely sensi- 

 ble, and when it is wounded, the animal is convulsed ; if it be cut 

 or compressed so that it cannot perform its functions, all the parts 

 of the body whose nerves arise below the point of injury are at 

 once paralysed. 



29. The cerebellum seems to be designed to regulate motion. 



30. The second portion of the nervous system, or NERVOUS 

 SYSTEM OF ORGANIC LIFE, communicates with the nerves which 

 arise from the spinal marrow by a great number of small fila- 

 ments, but it is distinct from it. 



31. This apparatus, which is also designated under the name 

 of yanglionic. system, or great sympathetic, on account of the con- 

 nection which it establishes between different parts of the body, 

 Is composed of a great number of small nervous masses called 



24 What is necessary to enable an animal to perceive impressions made 

 upon it? 



25. What occurs, if, from any cause, the functions of the brain be inter- 

 rupted ? 



26. What is remarkable in the origin of the nerves ? 



27. Is the brain itself'sensible ? 



28. Is the spinal marrow sensible or not ? When the spinal marrow 

 compressed or wounded^what occurs? 



2). What seem-s to be the office of the cerebellum? 



30. Does the nervous system of organic life communicate with the ner- 

 vous system of relation ? 



31. Why is the nervous system of organic life called the great sympa. 

 thetic ? Why is it also called the ganglionic system ? What is a ganglion ? 

 To what parts are those nerves distributed which arise from the ganglion*? 



