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 which chemical energy is set free, waste products — inert 

 chemical substances — are formed which if not eliminated from the ani- 

 mal system 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 important feature in 

 respiration. By another process the liquid and the solid waste is re- 

 moved. 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 transft^rmation. That the animal body is 

 so largely made up of solutions and gaseous substances is an important 

 factor in its relatively unstable chemical condition, a condition of uii- 

 stablc equilibrium, which determines the active and dynamic character 

 of the animal. Since, then, chemical activity 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 activi- 

 ties ; their orderly secjuence 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 hier- 

 archy in the forms of energy, chemical energy seems to belong to the 

 upper class; for though some forms of energy are not readily trans- 

 formed into chemical energy, chemical energy can be transformed into 

 all others. As a result the animal, being a chemical engine, has, as it 

 were, an "inside track" to the main sources of energy, 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 en- 

 ergy 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 en'^rgetics, a science which fur- 

 nishes the basis for the correlation of many diverse branches of knowl- 

 edge. 



The activities and transformations within the animal body show 

 us very clearly how an animal is dependent upon environmental condi- 

 tions. 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 interrelations of these 

 fundamental environmental units have been strikitigly expressed by 

 Powell ('95: 22-23) -'^ 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 



