108 LIFE AND DEATH. 



purely and simply, the energy brought into play, 

 consumed, or, better still, transformed in the active 

 organ, or tissue. Food as it is introduced, inert food, 

 does not, in fact, take up its place as it z's, without 

 undergoing changes in that organ and that tissue, in 

 order to restore the status quo ante. 



Before building up the tissue it will have undergone 

 various modifications in the digestive apparatus. It 

 will have also undergone changes in the circulatory 

 apparatus, in the liver, and in the very organ we are 

 considering. It is after all these changes that assimila- 

 tion takes place. It will find its place and will have 

 then passed into the state of reserve. 



The food digested, modified, and finally incorporated 

 as an integral part in the tissue in which it will be ex- 

 pended, is therefore in a new state, differing more or 

 less from its state when it was ingested. It is a part 

 of the living tissue in the state of constitutive reserve. 

 Its potential chemical energy is not the same as that 

 of the food introduced. It may differ from it very 

 remarkably in consequence of sudden alterations. 



We do not know for certain at the expense of what 

 category of foods this or that given organ builds up 

 its reserve stuff. There is a belief, for instancej 

 according to M. Chauveau, that the muscle does its 

 work at the expense of the reserve of glycogen which 

 it contains. The potential chemical energy of this 

 substance would be a source of muscular mechanical 

 energy. But we do not know exactly at the expense 

 of what foods, albumenoids, fats, or carbohydrates 

 the muscle builds up the reserve of glycogen expended 

 during its contraction. It is probable that it builds it 

 up at the expense of each of the three categories after 

 the various more or less simple alterations undergone 



