38 



THE HUMAN MECHANISM 



These walls are relatively thick in the arteries, usually some- 

 what thinner in the veins; in the capillaries, however, they 

 are very thin, and it is through these thin capillary walls 

 that all interchanges of matter take place. That the con- 

 nective tissue surrounding the capillaries bears an important 

 relation to the circulation we shall now see. 



10. The lymph spaces of the connective tissue ; the lymph. 

 Careful examination shows that the fine connective tissue 



within which the capillaries 

 are embedded is not a solid or 

 continuous mass, but rather 

 a mass or mesh of extremely 

 fine fibers or bundles of 

 fibers, with here and there 

 connective-tissue cells which 

 keep the fibers in repair. 

 The connective tissue, there- 

 fore, is everywhere channeled 

 by irregular spaces running 

 between the fibers and other 

 structures ; these spaces com- 

 municate freely with each 

 other and contain a colorless 

 liquid known as lymph ; the 

 spaces of the connective tis- 

 sue may thus be conveniently 

 described as lymph spaces. 

 They serve as communicating 

 channels between the cells and the walls of the capillaries. 



11. Origin of the lymph. The lymph which the spaces 

 contain is derived partly from water and soluble food mate- 

 rials which have passed through the capillary walls from the 

 blood and partly from material produced by the neighboring 

 cells (see the next chapter); on the other hand, the cells 

 absorb from the lymph substances which the latter has 



FIG. 29. Superficial and some deeper 

 lymphatics of the hand 



