lo PLANTS AND ANIMALS. 



general way that the insoluble proteids are converted into soluble 

 peptones, insoluble carbohydrates into sugars, and fats into soaps and 

 glycerine, though in some cases the fats are emulsified or broken into 

 minute particles which are then carried into the organism. 



The next important point to notice is the constitution of 

 foods. Leaving out of consideration the minerals, which 

 are only of secondary importance, we find that the simplest 

 animal- foods are complex compounds of carbon, hydrogen 

 and oxygen, and that others have these elements with the 

 addition of nitrogen, sulphur and phosphorus. An animal is 

 incapable of building up its protoplasm from any simpler 

 products. It would be easy to supply an animal with mineral 

 salts alone, such as nitrates, sulphates and carbonates, con- 

 taining all the chemical elements in protoplasm, but they 

 would be of no practical use to the animal in the formation 

 of fresh protoplasm. 



Plants and Animals. — On the other hand, it is 

 typical of plants that they can build up protoplasm from 

 such simple compounds as carbonic acid, water and mineral 

 salts, all of which are soluble and diffusible, either as gas 

 or hquid. 



Hence the primary distinction between a plant and an 

 animal rests in the power of the former to perform the 

 synthesis of compounds containing carbon, hydrogen and 

 oxygen from carbonic acid and water. This power resides 

 in the presence of chlorophyll, a green colouring matter, 

 which under suitable conditions of warmth and sunlight 

 can effect the important synthesis. From this we can 

 derive the other differences between animals and plants. 

 The food of animals being solid, they require digestive 

 organs to bring it into a condition suitable for absorption. 

 Again, they require motor organs, for solids of this nature 

 are in isolated masses (plants and other animals) and must 

 be sought for. 



The liquid and gaseous food of plants being already in 

 a condition for absorption (or assimilation) no alimentary 

 organs are required, and, being universally distributed, there 

 is no necessity for movement; the absence of movement 

 imphes a low condition of the function of sensation. 



We have already referred to the relationship between 

 the surface and the bulk of an animal, and in a typical 



