364 ANNUAL REPOET SMITHSONIAN INSTITUTION, 1933 



is the basis of life, is a continuous alternating series of making and 

 unmaking of complex molecules in protoplasmic substance (fig. 1). 

 Its constructive phase requires a constant supply of new building 

 material (food) and new energy; its destructive phase is accom- 

 panied by a quick union of some of the protoplasmic substance with 

 oxygen, and results in the liberation of energy and the production 

 of waste materials. Animal cells require relatively complex, energy- 

 containing food material, which normally is the source of most of 

 their energy released. Some of the latter is consumed within the 

 cells by the constructive processes of metabolism and growth, the 

 remainder is available for the work of the animal. The green cells 

 of plants take energy from the sun's radiation and build up energy- 

 Intake of Oxyo^ert 



Constructive X ^'^ \ Destructive 



Phase ■^--./ / \ V-''"PHase 



Disctiar'g'e of 

 __ „ _, Waste Products 

 Iixtake of 

 Energ-y-containingp / \"""~'- ReIeased Ener gy 



Food. Materials / ^ 



Intemally-Gonsumed 



Energ^^y" 



Figure 1. — Diagram of animal metabolism. 



containing compounds from simpler substances. Life is the spark 

 of surplus energy that escapes at each destructive phase of proto- 

 plasmic metabolism. The structural organizations of animals are 

 mechanical devices for the utilization of their vital energies. The 

 energy of life is not different from the forms of energy existing in 

 inanimate nature; the feature that distinguishes living matter from 

 nonliving matter is its chemical mechanism for furnishing a con- 

 tinual output of energy. A grain of powder once exploded is done 

 for ; the explosions of protoplasmic metabolism began with the origin 

 of life and will not cease until life is extinct, because each is accom- 

 panied by a constructive process that builds up a new explosive. 

 Life, in the physical sense should not be confused with consciousness, 

 which may or may not be an adjunct of living organisms, but is not 

 the cause of metabolism. 



Protoplasm itself is a soft watery substance, not at all remarkable 

 in appearance, and it is held in the form of cells only because each 

 mass is covered by a thin outer layer of denser material having a 



