320 PHYSIOLOGY AND HEALTH. 



whose backs have no other employment than to hold the 

 spine erect. 



734. The curvature of the spine not only injures the sym- 

 metry of the frame and lessens its height, but it distorts the 

 chest and diminishes its capacity, and interferes with the free 

 motions of the ribs. Accordingly, the lungs have less space 

 for rest and less room for expansion, and therefore can re- 

 ceive less air at each inspiration; then, imperfect purification 

 of the blood, and, lastly, a deficient nutrition of the body, 

 must necessarily follow. Sometimes serious diseases of the 

 lungs are brought on by this curvature of the spine, and 

 Dr. Hope says, " The majority of hump-backed persons are 

 ultimately attacked by disease of the heart." 



735. The rings in the vertebrae (Fig. XXXIV.) being placed 

 one upon another, form a channel or tube through the whole 

 spinal column. This channel is of the utmost importance in 

 the animal structure, for it encloses the great nerve called 

 the spinal marrow, that extends from the brain to the trunk 

 and the lower part of the. system, and supplies all these parts 

 with the principle of life. This great nerve begins in the 

 brain, and reaches to the end of the spinal column. In the 

 course of its descent, it sends out on each side nerves to the 

 heart and lungs, to the organs of digestion and of motion. 

 All the parts, therefore, of the trunk and all the extremities 

 depend, more or less, upon the healthy condition of this great 

 nerve for their fulness of life and freedom and energy of 

 action. 



736. Any change in the shape of the spinal column, or in 

 the relations of these bones to each other, must diminish the 

 capacity of this canal, and, of course, press somewhat upon 

 this great nerve. This pressure upon this nerve interrupts its 

 freedom of action, and interferes with the communication 

 between the brain and the parts of the body which receive 

 nerves through this channel. This must be the natural con- 

 sequence of all distortions of the spine, all permanent curva- 

 tures from side to side, and of all unnatural curvatures from 

 front to back, or from back to front. 



