120 PLANTS, THE FOOD OF ANIMALS 



sugar formation is not a direct result of constructive metabolism, 

 but rather a direct effect of destructive metabolism through 

 oxidation. In the test tube the chlorophyll is destroyed by 

 this chemical change, but chlorophyll in the test tube is quite 

 another matter from chlorophyll in the living leaf where, if such 

 reactions are necessary in the formation of sugar, they are 

 balanced by the synthesizing activity of the chromogen com- 

 plex (MgN 4 C32H 3 oO) in the presence of CO 2 and H 2 O and with 

 the energy of sunlight. The chromogen complex would thus 

 play the part of a synthesizing enzyme activated in both con- 

 structive and destructive phases by the energy of light. Pres- 

 ent knowledge, however, is very incomplete in regard to photo- 

 chemistry of the chloroplast, and such deductions, while allur- 

 ing, must be regarded as purely hypothetical, although no 

 more hypothetical than the long-accepted view of the direct 

 union of CO 2 and H 2 O in the formation of hexose sugars by 

 photosynthesis. 



From this point on in nutrition, animals and plants alike have 

 the power to manufacture proteins. In the plant, the process 

 can be followed more easily than in animals; some of the simpler 

 compounds like asparagin consist of nitrogen added to the 

 carbohydrate (C 4 H 8 N 2 O 4 ), and from this relatively simple 

 amide, protein may be formed by the addition of the essential 

 elements. The formation of these substances is obscure, the 

 action, presumably, being brought about through the agency of 

 synthesizing enzymes. In animals, the protein materials 

 taken as food provide the necessary elements for this synthesis, 

 but in plants the proteins must be built up step by step. Plants 

 thus are essentially constructive while animals are destructive. 



In the manufacture of starch more oxygen is liberated from 

 combination than can be used, and this diffuses through the 

 leaves and into the air, while carbon dioxide is taken in. 

 Plants and animals, therefore, would seem to be well adapted 

 for mutual existence side by side. But the plant does more or less 

 work and utilizes its substance in providing the energy neces- 

 sary for this work, while waste matters, in the form of CO 2 and 

 water and nitrogenous substances, are formed. As in animals, 



