28 ANATOMY AND PHYSIOLOGY. 



in water, so as to remove entirely the blood and oil which pervade 

 them, they become of a beautiful white. 



As bones are living parts, they of necessity are provided with 

 blood-vessels and nerves. On the surface of every bone may be 

 remarked an infinity of minute pores, into which small blood-vessels 

 run. If the surface of a bone be exposed in the living body by an 

 injury, it will be seen to bleed, and it can be colored artificially. 

 This coloration, however, is practicable only in young subjects, 

 where a great afflux of blood takes place to the bones, for their 

 growth ; in adult years, when they have reached their full size, and 

 have become hard and compact, much less blood in proportion cir- 

 culates through them. There is another very curious way in which 

 the vascularity of young bones can be demonstrated, by making the 

 blood itself the vehicle of the coloring matter with which they are 

 to be injected. If a young growing animal be fed for a fortnight or 

 so, on food in which a proportion of chopped madder is mixed, the 

 coloring principle of the madder will pass into its blood, arrive in 

 its bones, and there chemically combine with the lime, tinging the 

 bones of a beautiful rose color, which is permanent, even after the 

 bones have been cleaned and well washed in pure water. The 

 nerves which are distributed to bones are very trifling, so that in 

 the healthy state they may be said to be almost insensible ; but 

 when they become inflamed, their sensibility is so much exalted, 

 that the slightest touch causes excruciating agony. 



The bones are covered with a dense membrane called the peri- 

 osteum, which adheres strongly to them, serves to convey the blood 

 vessels to them, and sends prolongations into all the little holes 

 which exist in such numbers on their surfaces. It also serves as 

 the medium for the attachment of tendons and ligaments to them, 

 having these parts in a manner interwoven and confounded with its 

 outer surface. The periosteum has also a considerable share in 

 the growth of young bones, and in the growth or reparation of old 

 ones, when fractures or other injuries may have rendered that ne- 

 cessary. 



Bones assume every variety of shape, as may be expected from 

 the various places and offices which they are destined to fill. 

 These varieties have been reduced by anatomists to four classes : 

 1st, the long or cylindrical ; 2d, the broad or flat ; 3d, the short or 

 round ; and 4th, the mixed or irregular. The long bones are dis- 

 tinguished by their length, which greatly exceeds their other 

 dimensions. They are found only in the extremities, and are 



