140 STRUCTURE OF BONES. 



the heart and respiratory muscles depended on the 

 will, as that of the muscles of locomotion do, the 

 circulation of the blood and the process of breathing 

 would both have ceased whenever sleep or any 

 other cause overcame the power of attention, arid 

 life would in consequence have been extinguished. 



From the different constitution of the voluntary 

 and involuntary muscles, it is clear that the former 

 were designed for alternate activity and repose. 

 Had it so pleased the Creator, He could as easily 

 have rendered the one set of muscles incapable of 

 fatigue, as he has actually rendered the other ; but 

 then the powers of man would not have been in 

 harmony with the purpose of his existence. Inces- 

 sant muscular activity would not only have been 

 incompatible with the highest human enjoyment, 

 that arising from the gratification of the moral and 

 intellectual faculties, but it would have lacked ob- 

 jects on which to expend itself usefully, and, un- 

 guided by intellect, would only have served to over- 

 turn and destroy the best provisions of nature for our 

 happiness. 



CHAPTER VI. 



The Bones essential to Motion, and to the Security of the Vital 

 ^ Organs The Skeleton Bones are composed of Animal and 

 , of Earthy Matter The Animal Part the Seat of their Vitality 

 The Proportions between these vary at different Periods of 

 Life Vessels, Nerves, Life, Growth, and Decay of Bones 

 Advantages of their Vitality and Insensibility Their Adapta- 

 tion to contained Parts Conditions of Health Necessity of 

 Exercise. 



THE hardness, strength, and insensibility which 

 form the distinguishing properties of healthy bones 

 fit them in a remarkable degree for serving as a basis 



