THE VEINS. 205 



point could not be inserted between two of them, as, for 

 instance, in the deep layers of the skin which can hardly 

 be pricked anywhere with a needle without drawing blood. 

 It is while flowing in these delicate tubes that the blood 

 does its nutritive work, the arteries being merely supply- 

 tubes for the capillaries, through whose delicate walls 

 liquid containing nourishment exudes from the blood to 

 bathe the various tissues. Imagine a piece of the finest 

 lace, with all its threads consisting of hollow tubes, and 

 diminished twenty times in size, and you will have some 

 idea of the capillaries. 



The Veins. The first veins arise from the capillary net- 

 works in various organs, and like the last arteries are very 

 small. They soon increase in size by union, and so form 

 larger and larger trunks alongside the main artery of the 

 part, but there are many more large veins just beneath the 

 skin than there are large arteries. This is especially the 

 case in the limbs, the main veins of which are superficial, 

 and can in many persons be seen as faint blue lines through 

 the skin. 



Why the large Arteries usually lie deep. The heart 

 pumps the blood with great force into the arteries, and if 

 an artery is cut very rapid and dangerous bleeding occurs ; 

 the veins, if cut, do not bleed nearly so violently as an 

 artery of the same size. Hence it is less dangerous to have 

 a large vein than a large artery close under the skin. 



Point out a fact illustrating the closeness of the capillaries in 

 many parts of the body. What does the blood do as it flows through 

 the capillaries? 



Where do the first veins arise? What is their size? How do 

 they increase in size? Where do the larger veins lie? In what parts 

 of the body do we especially find large veins close beneath the skin? 



Why are the large arteries, as a rule, placed deeper than veins of 

 corresponding size? 



