112 PHYSIOLOGY AND HEALTH. 



solid and liquid matter a day ; and yet our weight does not 

 usually increase. Even after making this daily addition for 

 successive years, we weigh about the same at sixty as we did 

 at twenty. This food is digested and converted entirely, or 

 in part, into blood ; and this blood is converted- into flesh, 

 muscle, fat, nerve, &c. ; arid yet these organs^ and parts 

 remain of the same size. 



243. The diligent arteries are almost incessantly adding 

 atom after atom to these organs, and yei: do not enlarge 

 them. The object of their work is, -not merely to make new 

 atoms of flesh, but to make those which will supply the place 

 of other atoms, which have served their purpose in the living 

 body, and have been carried away. It has already been 

 stated ( 1, p. 9) that however long the body, as a whole, 

 may continue to live, none of its component particles can 

 enjoy any considerable duration of life. These particles are 

 deposited, by the arteries or the capillaries, in the various 

 organs and tissues ; and then they are endowed with life, 

 and the peculiar properties of the part in which they arc 

 placed. In the muscle, they have the power of contraction, 

 and in the brain, the power of feeling and perception; and in 

 the bone, they are hard and strong, and apparently in- 

 sensible. 



244. But in a little while this vitality, this property of 

 life, is exhausted, and the atom is dead^ Then it is removed, 

 and another atom takes its place, to go through the same 

 course of life, action, and death. This succession of parti- 

 cles, this change from life to death, and this renewal of life, 

 are constant, and almost universal, in the animal body. We 

 are dying, atom after atom, daily, hourly, momently ; and 

 we are renewed and revived in the same degree, and at the 

 same time. We enjoy, therefore, a constant freshness of 

 life. This is the united work of the arteries, which bring 

 the new and living atoms, and of the veins and absorbents^ 

 which carry the old and dead atoms away. The arteries 

 and veins have already been described. The absorbent ves- 

 sels seem to be spread throughout all the tissues. Wherever 



