36 



THE HUMAN MECHANISM 



chiefly of lifeless material containing large amounts of mineral 

 matter, with cells lying here and there in spaces which com- 

 municate with one another by means of minute channels. The 

 connective tissues, like that which binds the skin to the un- 

 derlying muscles or that which forms the sheath and septa of 

 glands and muscles, consist essentially of lifeless fibers run- 

 ning in all directions and thus ready to limit the extent of any 

 pull tending to separate unduly the adjacent organs. To organs 

 and tissues of this kind we may give the name of supporting 



organs and tissues, 

 and they form al- 

 most the sole excep- 

 tion to the general 

 rule that the essen- 

 tial part of a tissue 

 consists of its cells. 

 The latter state- 

 ment is true of all 

 organs and tissues 

 which do work 

 the active organs of 

 the body. In the 

 case of the support- 

 ing tissues the cells 

 which they contain 

 are the fundamental units of the organ, since they make the 

 intercellular lifeless substance ; but the part which the organ 

 plays in the work of the body as a whole is performed 

 by the lifeless substance (fibers, etc.) which the cells have 

 manufactured and keep in repair. 



9. The blood vessels are closed tubes in connective tissue. 

 The arrangement of connective tissues is fundamentally the 

 same in gland and muscle. These tissues serve the obvious 

 purpose of binding the anatomical units into organs, but 

 they also perform other functions equally important. 



FIG. 27. Longitudinal (A) and transverse (B) 

 sections of bone 



Showing the branching and communicating canals 

 in which are blood vessels and nerves surrounded 

 by the lifeless bone substance. In this are spaces 

 connected with one another by very minute channels. 

 Each of these spaces contains a living cell, shown in O 



