140 PHYSIOLOGY. 



phragm is paralyzed, and death sooner or later follows from 

 suffocation. $ If it be divided about the first dorsal vertebra, 

 then life may be maintained for a considerable time, although 

 the ribs cannot be elevated, as the intercostal muscles are 

 rendered paralytic.. Breathing is, however, kept up by the 

 action of the diaphragm. I have seen a man whose spine 

 was dislocated in this region, live seven or eight weeks. All 

 sensation and motion were lost in the parts below the seat of 

 the injury, but his reason and senses were perfect. 



13. As the heart, lungs, larynx, and many of the most im- 

 portant organs of the body are supplied with nervous influ- 

 ence by the eighth pair of nerves, or par vagum, why is it 

 that a division of the spinal marrow causes death ? This 

 question is easily answered, by remembering that one of the 

 functions of the par vagum is, to convey to the brain the 

 sense of the want of air, or of respiration, and that this 

 stimulus reacts upon those parts of the spinal cord which give 

 rise to the respiratory nerves of the chest,} Now if this com- 

 munication be cut off, the influence of the brain, or the me- 

 dulla oblongata, cannot be transmitted so as to excite those 

 muscles which are employed in breathing. 



14. That this is the true answer to the above question is 

 also shown by dividing the par vagum in the neck. This 

 causes palsy of the lungs, and also of the muscles which open 

 the larynx ; in consequence of which, the top of the wind- 

 pipe is immediately closed, and death follows from suffocation. 

 Besides this, it also prevents transmitting to the medulla o&- 

 longata, the sense of the want of respiration, and thus pre- 

 vents also the reaction of this part upon the spinal marrow. 



15. Does the spinal marrow exert any influence upon the 

 circulation of the blood ? (It is ascertained that the action of 

 the heart is nearly independent of the spinal marrowj Its 

 nervous influence is derived from the par vagum and the 

 great sympathetic nerve, the former of which has but little 

 connection with the spinal cord. The whole spinal marrow 

 has been removed, and still the heart has continued to act. 



