24 MAMMALIAN ANATOMY 



with these colors in order to show the course and distribution of the 

 blood-vessels. 



Weight. The dried bone is light: its coverings have been stripped 

 off, and the softer part of the bone substance, the marrow, the blood- 

 vessels, and the nerves, which fill its interior, have been removed, and 

 their place is taken by air. The actual weight of bones varies with 

 their size ; their relative weight varies with the density, or com- 



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pactness, of the bone tissue. When the weight of a bone is compared 

 with the weight of an equal volume of distilled water, the result is 

 known as the specific gravity of bone. Hence if the weight of the 

 bone's volume of water be put at 1, the weight of the bone in a fresh 

 state will be found to vary from 1.87 to 1.97. 



Odor. A perfectly clean bone should be odorless ; usually, how- 

 ever, a faint odor can be detected, due to the chemicals used in cleaning, 

 or to the dried and partially decomposed particles in the medullary 

 cavity, or in the bone substance. 



Hardness. With the single exception of the teeth, bone is the 

 hardest substance in the animal body. If the central part of a 

 long bone be cut with a sharp knife, it will be noticed that the hard 

 tissue is thick and dense, but if the end be shaved the hard tissue 

 will soon be cut through and a spongy tissue exposed. Thus there 

 is a difference in hardness in different parts of a bone. There is 

 also a difference in the hardness of different bones. 



Strength. A dried long bone can be easily broken. This, how- 

 ever, is not a fair test of strength, inasmuch as it has lost many 

 toughening qualities ; nor are the living conditions by any means 

 present under experiments to show the weight which a piece of bone, 

 fresh or dried, will support before crushing, or the number of pounds 

 which can be suspended from it before its fibres separate. 



Elasticity. It will be noticed that the bone under examination 

 can be bent slightly and when released will assume its original form. 

 If it be dropped end downward on the floor, it will rebound. These 

 facts show that it possesses elasticity, the power of returning after 

 pressure to the original form and size. 



External Appearance. If the surface of the bone be now exam- 

 ined more closely, it will be seen to be for the most part smooth and 

 shining and covered by very fine lines and minute holes ; nearer the 

 ends, however, it is rougher and more porous. Roughened lines and 



