MATTER AND ENERGY 87 



plant protoplasm, however, while it performs 

 this operation, also, in connection with its 

 own special activities, sets free kinetic energy. 

 Thus certain of the parts of plants produce 

 heat, and energy may appear as motion, 

 when rootlets press through the soil, or when 

 certain parts move. Still the main relation of 

 plant life to energy is that it stores it up, or 

 renders it potential. 



45. Chemical Phenomena of Animal Life. 

 The activities of an animal are mainly of an 

 opposite kind. The animal lives on plants 

 or upon the tissues of other animals. Animal 

 protoplasm cannot exist on ammoniacal 

 compounds, water, and saline matters alone. 

 It has little or no power of forming those 

 into more complex substances. But it 

 takes proteins, carbo-hydrates, and fats, 

 and along with saline matters and water it 

 builds these up into its own protoplasm. It 

 may possibly use them to some extent 

 directly, that is to say, without incorporation 

 into its protoplasm, but this is doubtful. 

 It is probable that there is a true incor- 

 poration, but, before incorporation, the 



