174 



APPLIED PHYSIOLOGY 



Arrangement of capillaries. 



a smallest artery. 



b smallest vein. 



c network of capillaries. 



laries is about three hundred times that of the arteries, 

 and hence the blood pressure is much less than in them ; 



yet the pressure is always 

 sufficient to keep the blood 

 in steady motion. 



302. Action of the white 

 blood cells in the capil- 

 laries. Often a white blood 

 cell will adhere to the wall of 

 the capillary and partially block 

 the blood stream for a moment. 

 It may work its way through 

 the wall of a capillary, and yet 

 leave no hole behind it. Many 

 are thus found in the spaces 

 outside the capillaries, and are 

 finally returned to the heart by 

 means of another set of tubes 



called lymphatics. When a capillary is injured, many of the white 



cells adhere to the injured spot and furnish food for its repair. They 



may even grow and change 



to connective tissue for its 



further repair. 



303. Diffusion of blood 

 plasma in the capillaries. 



The slight pressure to 

 which the plasma is sub- 

 jected is just sufficient to 

 cause it with its albumin 

 to diffuse through the ex- 

 ceedingly thin wall of the 

 capillary. It fills the 



spaces between the capillary network and bathes each cell 

 of the body with an abundant supply of nourishment. 



Diagram showing how food reaches the 

 cells from the capillaries. 



