SYNTHESES IN THE BODY. 



Experiments made by adding various combustible sub- 

 stances, as sugar, to fresh blood, also fail to prove the oc- 

 currence of any oxidation of such bodies in that liquid. 



Tissue-Building and Energy- Yielding Foods. The- 

 Human Body, like that of other animals, is, on the whole, 

 chemically destructive; it takes in highly complex sub- 

 stances as food, and eliminates their elements in much 

 simpler compounds, which can again be built up to their 

 original condition by plants. Nevertheless the Body has 

 certain constructive powers; it, at least, builds up protoplasm 

 from proteids and other substances received from the- 

 exterior; and there is reason to believe it does a good deal 

 more of the same kind of work, though never an amount 

 equaling its chemical destructions. Given one single pro- 

 teid in its food, say egg albumen, the Body can do very 

 well; making serum albumen and fibrin factors out of it 

 for the blood, myosin for the muscles, and so on : in such 

 cases the original proteid must have been taken more or 

 less to pieces, remodeled, and built up again by the living 

 tissues; and it is extremely doubtful if anything different 

 occurs in other eases, when the proteid eaten happens to be- 

 one found in the Body. In fact, during digestion the pro- 

 teids are broken down somewhat, and turned into peptones; 

 in this state they enter the blood and must again be built 

 up into proteids, either there or in the solid tissues. 



The constructive powers of the Body used to be rather 

 too much ignored. Foods were divided into assimilable and 

 combustible, the former serving directly to renew the organs 

 or tissues as they were used up, or to supply materials for 

 growth; these were mainly proteids and fats; no special 

 chemical synthesis was thus supposed to take place, the 

 living cells being nourished by the reception from outside of 

 molecules similar to those they had lost. Fat-cells grew 

 by picking up fatty molecules, like their contents, received 

 from the food; and protoplasmic tissues by the reception 

 of ready-made proteid molecules, needing no further 

 manufacture in the cell. The combustible foods, on the 

 other hand, were the carbohydrates and some fats: these, 

 according to the hypothesis, were incapable of being made? 



