THE SPINAL MARROW AND ITS FUNCTIONS. 139 



process occupies but an instant.?" Thus we have two channels 

 of nervous influence ; the one transmitting intelligence to 

 the mind, the other conveying the purposes of the will to the 

 muscles necessary to carry them into effect. 



10. That such is the chief function of the spinal marrow, 

 is proved by the well-known fact, jthat if it is divided 

 in any part of its course, that portion of the body, as well 

 as the limbs, which are situated below the seat of the 

 injury, will be paralyzed ; that is, all sense and motion will 

 be lost, while the parts above the injury will be unaffected. 

 Jf the injury occur very high up in the neck instant death 

 will ensue,|because the nerves, which go the diaphragm and 

 are necessary to carry on breathing, are separated from their 

 connection with the brain. These leave the spine as high 

 as the third vertebra of the neck. 



11. I have stated that it has been proved, that the 

 ^principle of motion resides to some extent in the spinal 



marrow itself. | This is shown by the following experiment. 

 If after the spinal cord be divided in the neck, and then lower 

 down in the back, we irritate any -of the muscles which are 

 supplied with nerves from this isolated segment, motion will 

 be produced. If the foot, or the hand be pricked, it will im- 

 mediately contract ; and this contraction is produced by the 

 irritation being transmitted to that portion of the spinal mar- 

 row, from whence the nerves of the part arise, and whose 

 connection with the brain has been severed, and then an im- 

 pulse is sent back again from this portion to the muscles of 

 the hand or foot which causes them to contract. Still, all 

 voluntary motion, as well as sensation, depend on the brain. 



12. If the medulla oblongata is injured, breathing imme- 

 diately ceases. If the spinal marrow is severed opposite the 

 second bone of the neck, death also speedily follows ; because 

 the nerves of respiration are cut off from their connection 

 with the part above. If the spinal cord be divided, as low as 

 the fifth cervical bone, thcn(lif3 will not be immediately de- 

 stroyed ; but the breathing will be difficult ; because the dia. 



