Thus plants are fed in great part by their leaves, taking an important part of their nourishment from the air, while by their roots they draw from the earth the water, the phosphates, the mineral salts, and the nitrates required for the formation of their albuminoid constituents. A vegetable is a laboratory in which is carried out the process of organic synthesis by which mineral materials are changed into organic matter. The first synthetic reaction is the formation of a molecule of formic aldehyde, CH_2O, by the combination of a molecule of water with an atom of carbon. From this formic aldehyde, or formol, we may obtain all the various carbohydrates by simple polymerization, i.e. by the association of several molecules, with or without elimination of water. Thus two molecules of formol form one molecule of acetic acid, 2CH_2O = C_2H_4O_2. Three molecules of formol form a molecule of lactic acid, 3CH_2O = C_3H_6O_3. Six molecules of formol represent glucose and levulose, 6CH_2O = C_6H_{12}O_6. Twelve molecules of formol minus one molecule of water form saccharose, lactose, cane sugar, and sugar of milk, 12CH_2O = C_{12}H_{22}O_{11} + H_2O; _n_ times six {10} molecules of formol minus one molecule of water, _n_(C_6H_{10}O_5), form starch and cellulose. Animals derive their nourishment from vegetables either directly, or indirectly through the flesh of herbivorous animals. The mineral matter, rendered organic in its passage through a vegetable growth, is finally returned by the agency of animal organisms to the mineral world again, in the form of carbonic acid, water, urea, and nitrates. Thus vegetables may be regarded as synthetic agents, and animals and microbes as agents of decomposition. Here also the difference is only relative, for in certain cases vegetables produce carbonic acid, while some animal organisms effect synthetic combinations. Moreover, there are intermediary forms, such as fungi, which possessing no chlorophyll are nourished like animals by organic matter, and yet like vegetables are able to manufacture organic matter from mineral salts. The work of combustion begun by the animal organism is finished by the action of micro-organisms, who complete the oxydation--the re-mineralization of the chemical substances drawn originally from the inorganic world by the agency of plant life. To sum up. Vegetables obtain their nourishment from mineral substances, which they reduce, de-oxydize, and charge with solar energy. Animal organisms on the contrary oxydize, and micro-organisms complete the oxydation of these substances, returning them to the mineral world as water, carbonates, nitrates, and sulphates.