CHAPTER IX. 



METABOLISM. 



THE food which has been properly digested within the stomach, 

 and intestines is absorbed by the chyle vessels and by the small 

 capillaries, whose union forms the portal vein. When once in the 

 blood-stream, it circulates with the blood-current, which carries it to 

 all of the various organs and tissues of the body. The absorbed nutri- 

 tive products are held in solution within the plasma of the blood. 



In order to nourish the structures outside of the vessel-walls, the 

 plasma, with its contained nourishment, is constantly being passed 

 through the capillary walls into the spaces between the living cells. By 

 this provision each cell is bathed in a plentiful supply of lymph, from 

 which medium it absorbs its nourishment. 



The various stages of the nutritive process viz., the transudation 

 of the nutritive plasma from the blood, the assimilation of parts of 

 this by the tissue under repair, the absorption of the other portion by 

 the lymphatics, and, last, the reabsorption of the final residue together 

 with that of the waste products of the tissues by the veins are per- 

 formed simultaneously and continuously in the living body. With the 

 entire organism in a healthy condition there is a perfect balance of 

 action. 



Action and use are always followed by a corresponding amount 

 of waste. The machinist must be making repairs to the locomotive or 

 other machine that is in use. So the tissues of the body are con- 

 tinually being destroyed, to pass away as effete matters, due to exercise 

 and action of the various organs of the economy. Thus, the simple 

 movement of the finger, our very thoughts and reasonings, are produc- 

 tive of waste in the tissues concerned. 



It is due to the repair by the machinist that the machine is 

 kept in normal running order.; likewise it is to the proper absorption, 

 assimilation and elimination of foodstuffs taken into our own 

 economies, that the body owes its normal function and health. 



The digested products, having arrived at their destination in 

 the organs and tissues, undergo two kinds of chemical processes in 

 the presence of oxygen, and under the peculiar activity of the cells. 

 The one is anabolism, or upbuilding; the other catdbolism, or destruc- 



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