62 



APPLIED PHYSIOLOGY 



114. Capillaries. The end of each artery divides into a 

 number of fine tubes called capillaries. The capillaries 

 make a network so fine that they touch every cell of the 

 body. The point of a needle cannot prick the skin with- 

 out bursting some of the capillaries and so drawing blood. 

 Each capillary has sides so thin and soft that the liquid 



parts of the blood easily 

 soak through to reach the 

 cells, and even the white 

 blood cells burrow through 

 its sides without harming 

 the tube. The capillaries 

 are only just large enough 

 to let the blood cells 

 pass through. 



115. How to see the 

 capillary circulation. 

 The web of a frog's foot 

 is very thin and clear, and yet contains many capillaries. 

 If it is spread out untler a microscope, you can see 

 the blood as it shoots through the tiny tubes. You can- 

 not see the liquid part, for it is like water, but you will 

 see the red blood cells, which, in the frog, are egg-shaped. 

 They will pass through the larger tubes in a stream too 

 rapidly for you to see the separate cells. In the smallest 

 tubes, a cell may get stuck crosswise for a moment and 

 stop up the whole tube, but it soon becomes free again 

 and passes on. Sometimes a cell starts to go through, 

 when a little movement of the leg will press it back again. 

 You should get your teacher or some physician to show 

 you this circulation. This will help you to remember 

 that millions of these tiny streams are continually flowing 

 through every part of your body. 



Diagram showing how food reaches the 

 cells from the capillaries. 



