16 



but Ivvo cases, in wliich the natural backward flexure of the loins 

 was increased so as to amount to distortion. 



"When curvature of the spine has existed for any length of time, 

 the bodies of llie vertebrce, which are concerned, conform to the 

 wrong inclination the spine has assumed. They are rendered thin, 

 on one side, by absorption ; whilst the other side preserves, or iu 

 some places exceeds, its natural thickness. When any consider- 

 able curvature has existed for a length of time, it necessarily induces 

 a second in an opposite direction of some other part of the spine ; 

 and this asain often eives rise to a third in the direction of the 

 first. 



The means, which are most commonly supposed to be necessary 

 for avoiding deformities of the spine are, I believe, those which 

 ha\ e Ihe greatest share in producing the usual spinal curvature. I 

 allude to the attempts which are made to oblige young people to 

 maintain the body immoveably in the erect posture ; and to the 

 restraint, which is imposed on the developement of the trunk, and 

 the exercise of its muscles, by the early use of stays. 



Il may not be improper to state some physiological principles, on 

 which the above opinion is founded. 



It is a well known law of nniscular action, that it cannot be 

 maintained without intervals of repose. No determination will 

 enable a person to hold the arm, in the extended position, more 

 than a few minutes. The sensation of fatigue is more intoler- 

 able than the greatest pain. We have frequent opportunities of 

 seeing this exemplified during surgical operations. 



It is generally acknowledged, that muscles are strengthened by be- 

 ing exercised ; but the difference between the ordinary actions of 

 muscles, and those attended with effort, has been overlooked. The 

 bulk and strength of muscles are not increased by the customary 



