THE CARE OF THE DOG'S SKIN. 



119 



are constantly going on, with the result that useful and 

 harmful products are being constructed. This, if not the 

 essence of life, is inseparable from all vital processes. 

 The animal in all its parts is built up from its food, but 

 sooner or later the whole fabric is renewed completely ; 

 as a matter of fact, the building up and tearing down go 

 hand in hand, and constitute what physiologists term the 



FIG. 5. PAPILLAE OF SSIN OF PALM OF HAND (AFTER SAPPEY). 



A vascular network in all cases, and in some nerves and tactile corpuscles, enter 



the papillae. 



metabolism of the body. Science can not at present trace 

 all the changes a piece of meat undergoes from the time it 

 enters the body till it leaves it. There are no doubt very 

 many intermediate bodies formed of which we are as yet 

 ignorant. But we do know part of the story. The meat is 

 digested or changed to blood albumin ; this is assimilated or 

 built up into the different parts of the body, and is finally 

 broken down and expelled in forms of relative chemical 

 simplicity. 



Taking food as a whole, it may be considered as reap- 

 pearing in the waste of the body (excretions) largely as 

 water, carbon dioxide (usually called carbonic-acid gas), 



