148 THE CELL 



hydrates, and convert these again into fats and albuminous sub- 

 stances, supply to the animal organism the ternary and quater- 

 nary substances which are necessary for its nutriment, and which 

 it is unable to elaborate, as the plants do, from such simple sub- 

 stances. In this manner the vegetable and animal kingdoms con- 

 stitute a life cycle, in which they assume opposite positions and 

 complement each other. This antithesis may be formulated as 

 follows : 



In the green plant cell the organic substance is formed syn-> 

 thetically from carbon dioxide and water, whilst the vital force 

 which is obtained from the sunlight becomes potential ; on the 

 other hand, the animal cell uses as nutriment the ternary and 

 quaternary compounds formed in the vegetable kingdom, for the 

 most part oxidising them. By this means it reconverts the 

 potential energy stored up in the complex compounds into vital 

 energy whilst performing work and evolving heat. The plant, 

 whilst its chlorophyll is exercising its function, absorbs carbon di- 

 oxide, and gives off oxygen ; the animal breathes in oxygen, and 

 breathes out carbon dioxide. In the chemical processes of the 

 plant reduction and synthesis predominate, whilst in those of the 

 animal oxidation, combustion and analysis are most important. 



However, from this one example of antithesis occurring in the 

 economy of nature between the animal and vegetable kingdoms, 

 it must not be concluded that plant and animal cells are quite 

 opposed in all their ordinary vital phenomena ; for this is not 

 true. Close investigation shows that there is universal unity in 

 the fundamental processes of the whole organic world. The 

 above-mentioned difference is only due to the fact that the plant 

 cell has developed a special faculty which is lacking in animal 

 cells, namely, the power of decomposing carbon dioxide by means 

 of its chlorophyll. With the exception of this one function, exer- 

 cised by chlorophyll, many of the metabolic processes which 

 are essential for the maintenance of life are performed in the 

 protoplasm in a perfectly similar manner in both plant and 

 animal cells. 



In both the protoplasm must breathe, take up oxygen, evolve 

 heat, and give up carbon dioxide if the vital processes are to be 

 carried on. In both plants and animals the decomposition and 

 reconstruction of protoplasm follow one another, and complicated 

 processes of correlated chemical analysis and synthesis occur. 



This similarity can be more easily understood when it is re- 



