, 



SITTING. 283 



The sitting posture, even without the support of the 

 back, can be maintained much longer than that of stand- 

 ing, because the centre of gravity is thrown nearer the 

 base ; and because the weight is diminished, and conse- 

 quently the muscular power required to support the erect 

 posture, is lessened. But this position, without the sup- 

 port of the back, after a time, becomes too painful to be 

 endured with patience. 



The sad consequences of long confinement in the sit- 

 ting posture, without any support for the back, have 

 already been described at some length, under another 

 head, but the more we have thought upon, and examin- 

 ed this subject, the more important it appears, and we 

 cannot therefore, in duty to the youth of our country, 

 dismiss it, without some further considerations and re- 

 marks. 



Causes of Spinal Curvatures. It is proposed here to 

 trace the effects of the causes to which we have already 

 referred with respect to curvatures of the spine, and to 

 show why certain positions will make this deformity 

 permanent. 



The spine itself, detached from all other parts, is fig- 

 ured and described at p. 84, Fig. 63, where the light col- 

 ored transverse lines between each two vertebrae, 

 show the cartilages of the spine. These cartilages are 

 in the young subject, about the fourth of an inch in 

 thickness, and are compressible, and elastic like pieces 

 of India rubber. Were it not so, the spine would be 

 rigid, and, unyielding as though it was formed of one 

 continued piece of bone. Its motions therefore are in 

 consequence of the elasticity of these cartilages, so that 

 when the spine is bent, one of their sides, or edges, are 

 compressed more than the other. 



In the night, when we take the recumbent posture, 

 and there is no pressure on the spinal column, these 

 elastic plates swell and become thickened, but their 

 thickness is again reduced by the weight of the body 

 during the day, and especially in laborers who carry 

 weights on their heads. The diurnal difference in the 

 thickness of each cartilage, from these causes, it is true, 

 is very slight, but their number is such, as to make an 



