ilETAEOLISM IX ANIMALS AND PLANTS. 19 



4. The chemical constituents and the 'metabolic 2>rocesses in animals 

 and plants present, on the whole, important features of difference. I 

 Formerly great importance was attached to the fact that plants 

 consist chiefly of ternary (non-nitrogenous) compounds, while animals 

 consist of quaternary nitrogenous compounds ; and a greater impor- 

 tance was attached in the former to the carbon, in the latter to the 

 nitrogen. But ternary compounds are found to be largely present 

 in the animal body, e.g., fats, carbohydrates ; while, on the other hand, 

 quaternary proteids play an important part in those parts of a plant 

 which are especially active in growth. Protoplasm found in the 

 living vegetable cell is richly nitrogenous, and of an albuminous 

 nature; and it agrees in its micro-chemical reactions with sarcode, 

 the contractile substance of the lower animals. In addition, the 

 modifications of egg albumen, known as fibrin, albumen, and casein, 

 are also found in vegetable cells. Finally, it is not possible to 

 mention any substance which is universally and exclusively found 

 either in animals or in plants. Chlorophyll (green colouring matter 

 of leaves) occurs in the lower animals (Stentor, Hydra, Bonellia), 

 while, on the other hand, it is totally absent in Fungi. Cellulose, 

 a peculiar non-nitrogenous substance found in the outer membranes 

 of vegetable cells, occurs in the mantle of Ascidians. Cholesterin, 

 and certain substances especially characteristic of nervous tL'sre~, 

 are also found in plants (Leguminosse). 



Of far greater importance is the difference in the nourishment and 

 metabolic processes. Plants take up with certain salts (phosphates 

 and sulphates of the alkalies and earths) more especially water, 

 carbonic dioxide (carbonic acid), and nitrates or ammonia compounds, 

 and build up organic compounds of a higher grade from these binary 

 inorganic substances. . Animals, in addition to taking up water and 

 salts, require organic food, especially carbon compounds (fat) and 

 nitrogenous, albuminous substances; which, in the cycle of metabo- 

 lism, break down to nitrogenous waste products (amides and acicls) T 

 kreatin, tyrosin, leucin, urea, etc. ; uric acid, hippuric acid, etc. Plants 

 exhale oxygen, whilst they are decomposing carbon dioxide by means, 

 of their chlorophyll under the influence of light, and are forming in 

 their chlorophyll corpuscles organic substances from carbon dioxide 

 and solutions containing combined nitrogen. Animals take up oxygen 

 through their respiratory organs for the maintenance of their meta- 

 bolism. The processes of metabolism and of respiration, therefore, in. 

 the two kingdoms are indeed mutually determinant, but have aa 

 exactly opposite result. The life of animals depends on the analysis 



