32 



APPLIED BIOLOGY 



Later we shall see small branches of the three veins in various parts 

 of the body. In fact every organ which has an artery in which 

 blood comes from the heart must have a vein for the return of 

 blood to P the heart; for the blood circulates from heart to arteries, 

 from arteries to smaller tubes called capillaries, from these to veins, 



FIG. 6. Diagram of chief arteries of 

 frog, p, to lungs ; c, to skin ; b, to 

 arm ; I, to head ; m, to digestive 

 organs ; a, aorta ; r, to kidneys ; 

 i, to legs. (From Thomson, after 

 Ecker.) 



Fitf. 7. Diagram of chief veins of 

 frog, j, from head ; b, from arm ; 

 c, from skin ; p, from lungs ; h, from 

 liver and digestive organs (i); k, 

 from kidneys ; /, s, from legs. (From 

 Thomson, after Ecker.) 



and thence back to the heart. See diagrams of the circulation in 

 Figs. 6 and 7. 



(D) Capillaries. Watch the flowing of blood through the 

 capillaries in the tail of a small tadpole allowed to lie on its side on 

 a wet plate of glass, or in the spread web of a frog's foot. Use low 

 power of microscope. 



In addition to the system of blood-tubes carrying blood from the 

 heart, through the capillaries in all organs, and back again to the 

 heart, there are H all organs many small tubes which collect a 

 watery fluid called lymph. This fluid is derived from the liquid 

 part of the blood, and it ultimately flows back into the blood. 



