128 PLANTS, THE FOOD OF ANIMALS 



with chlorophyll; the rhizome elongates by apical growth 

 through the ground, until the young fern plant is fully estab- 

 lished and is ready to make and store up starch. The prothal- 

 lium gradually shrivels up and disappears. 



The work done by the fern is duplicated by every type of 

 plant life provided with chlorophyll. Sugars, starches, proteins 

 and lifeless woods are manufactured and stored in roots, fruits, 

 seeds, and trunks, and with them is locked up the potential energy 

 to be transformed into kinetic energy through physiological 

 and physical combustion by man and the lower animals. Noth- 

 ing is wasted in the life cycle of matter and energy. Sugars, in 

 addition to their food value for animals and plants, in the 

 presence of yeast are transformed into alcohol and carbon di- 

 oxide, and their contained energy is changed into heat, energy 

 of yeast protein and that of alcohol. Alcohol, in the presence of 

 bacteria, is turned into acetic acid, the potential energy being 

 converted into that of bacteria protein and that of acetic acid. 

 The latter is acted upon again by bacteria, and changed into 

 carbon dioxide and water in which the contained energy is nil, 

 the bacteria protoplasm again storing up that which was con- 

 tained in the acetic acid. 



The proteins, carbohydrates and fats, derived mainly from 

 plants, in the last analysis are the main foods of all animals 

 and their chief sources of energy. Both plants and animals re- 

 lease the stored energy in the form of heat, light, electricity or 

 movement, and in metabolism give off nitrogenous waste, car- 

 bon dioxide, and water. Of these, only the nitrogenous sub- 

 stances retain some energy of combination. Under the action of 

 bacteria this small store is transformed into energy of bac- 

 terial protein, while free ammonia, carbon dioxide and water 

 are returned to the earth and the air (NH 2 )-2CO -f- 2H 2 O 

 = 2NH 3 + CO 2 + H 2 O. The proteins of the dead bodies of 

 plants and animals, after furnishing food and energy for scaven- 

 gers of many kinds, are finally attacked by the army of nitrify- 

 ing and other bacteria, and slowly transformed into nitrites, 

 nitrates, sulphates, phosphates and other salts, and into free 



