CHAPTER XVI. 



NUTRITION AND THE METABOLIC CHANGES 

 IN THE TISSUES. 



The scene of activity is now shifted from the alimentary 

 system, from the liver, and even from the circulating blood 

 and directed to the individual living cells wherever in the 

 body they may occur. Here the most vital part in the his- 

 tory of the foods is played; it is here where the food is 

 built into new tissues ; it is here where the energies of the 

 body are liberated. 



A number of perplexing questions at once present them- 

 selves, the solution of which in every case is not yet forth- 

 coming. Are all of the foods taken into the body built up 

 into living tissue, or are some of them merely oxidized 

 without ever becoming an integral part of the body ? Is 

 the energy derived by a direct oxidation of these foods, or 

 is the energy a result of the disintegration of living ma- 

 terial ? When oxygen and its properties were first dis- 

 covered by Priestly and Lavoisier, the conclusion seemed 

 irresistible that the oxidations of the body occurred in the 

 lungs. According to this view it was explained that the 

 animal heat originated here, and was by the circulating 

 blood carried over the body, and in this manner the neces- 

 sary energy for bodily work distributed. It was, however, 

 soon found that the blood coming from the lungs was not 

 warmer than that going to the lungs, and so this view had 

 to be abandoned. The seat of oxidation was later placed 

 in the blood, then in the liver, then in other organs; but 

 there is no question at all now but that the seat of oxidation 

 is in the individual living cells in the various tissues all 

 over the body. It is in the living tissues where the union 

 of the foods and the oxygen occurs. 



(365) 



