ANIMALS AND THEIR ENVIRONMENTS ADAMS. 517 



pounds, and thus concentrates powerful chemical energy in such a 

 form that the animal, by a further change, is able to set it free and to 

 utilize it. Sugar, starch, and gluten are familiar examples of this 

 " tablet " or " cartridge " form of chemical energy which animals 

 explode or set free and then use in maintenance. During this trans- 

 formation, in v\'hich chemical energy is set free, waste products — 

 inert chemical substances — are formed which if not eliminated from 

 the' animal sj'stem will prevent its operation, just as ashes if not 

 removed will check a furnace. Respiration aids in the removal of 

 carbonic-acid gas — a waste product — from the body, but we often 

 forget that the chemical energy derived from the oxygen is an im- 

 portant feature in respiration. By another process the liquid and 

 the solid waste is removed. Thus gases, liquids, and solids are taken 

 into the body and later returned to the environment in a different 

 chemical condition, thus completing a cycle of transformation. That 

 the animal body is so largely made up of solutions and gaseous sub- 

 stances is an important factor in its relatively unstable chemical con- 

 dition, a condition of vmstaMe equilibriuTn,, which determines the 

 active and dynamic character of the animal. Since, then, chemical 

 acti^dty is one of the essential characteristics of a living organism, its 

 influence forms one of the main problems of the zoologist when 

 studying the changes in animal activities, their orderly sequence, and 

 the laws which govern them. 



On account of the fact that the animal is a chemical engine, it is 

 able to use chemical energy to the fullest extent. If we assume a 

 hierarchy in the forms of energy, chemical energj^ seems to belong 

 to the upper class; for though some forms of energy are not readily 

 transformed into chemical energy, chemical energ}^ CEin be trans- 

 formed into all others. As a result the animal, being a chemical 

 engine, has, as it were, an " inside track " to the main sources of en- 

 ergy, and thus by transformation is able to utilize chemical energy 

 to form light, as in the firefly, or electricity, as in the electric eel ; and 

 other forms of energ}^ useful to the animal are similarly derived. 

 This study of the activities of living animals, as contrasted with the 

 study of dead ones, is a phase of the general science of energetics, 

 a science which furnishes the basis for the correlation of many di- 

 verse branches of knowledge. 



The activities and transformations within the animal body show 

 us very clearly how an animal is dependent upon environmental 

 conditions. The animal transforms air, water, and rock, and all 

 animal habitats and environments must contain these elements. In 

 nature these are combined in a multitude of ways. The interrela- 

 tions of these fundamental environmental units have been strilringly 

 expressed by Powell (1895:22-23) as follows: 



The envelopes of air, water, and rock are so distinct that they can be 

 clearly distinguished ; and yet, when they are carefully studied, it is dir,covei-ed 

 65133°— SM 1917 34 



