DIFFERENCES BETWEEN ANIMALS AND PLANTS. 23 



theoretically, invariably true, it would nevertheless be prac- 

 tically impossible to apply it to the greater number of those 

 minute organisms concerning which alone there can be any 

 dispute. 



As a broad rule, all plants are endowed with the power of 

 converting inorganic into organic matter. Thzfood of plants 

 consists of the inorganic compounds, carbonic acid, am- 

 monia, and water, along with small quantities of certain 

 mineral salts. From these, and from these only, plants are 

 capable of elaborating the proteinaceous matter or protoplasm 

 which constitutes the physical basis of life. Plants, there- 

 fore, take as food very simple bodies, and manufacture them 

 into much more complex substances. In other words, by a 

 process of deoxidation or unburning, rendered possible by 

 the influence of sunlight only, plants convert the inorganic 

 or stable elements ammonia, carbonic acid, water, and 

 certain mineral salts into the organic or unstable elements 

 of food. The whole problem of nutrition may be narrowed 

 to the question as to the modes and laws by which these 

 stable elements are raised by the vital chemistry of the 

 plant to the height of unstable compounds. To this gene- 

 ral statement, however, an exception must seemingly be 

 made in favour of certain fungi, which require organised 

 compounds for their nourishment. 



On the other hand, no known animal possesses the power 

 of converting inorganic compounds into organic matter, but 

 all, mediately or immediately, are dependent in this respect 

 upon plants. \ All animals, as far as is certainly known, 

 require ready-made proteinaceous matter for the mainten- 

 ance of existence, and this they can only obtain in the first 

 instance from plants. Animals, in fact, differ from plants 

 in requiring as food complex organic bodies which they 

 ultimately reduce to very much simpler inorganic bodies. 

 The nutrition of animals is a process of oxidation or burn- 

 ing, and consists essentially in the conversion of the energy 

 of the food into vital work ; this conversion being effected 



