656 SCIENCE PROGRESS 



change, by active, compensatory adaptations of its functioning ; 

 capable of indefinite growth by accretion and dissociation 

 (reproduction); and effecting energy-transformations without 

 cessation (for in the general sense the organism does not die). 

 The definition withstands criticism. We cannot here defend 

 it in detail, and all we are immediately concerned with is the 

 conception of the organism as a system in which compensatory 

 energy-transformations proceed. We can show that it conforms 

 to the two laws of thermodynamics, but the second law must 

 be regarded as having a double sign. 



The body of a plant or animal is a system conforming strictly 

 to the law of conservation. 1 If the weight of an animal remains 

 constant, there is an exact balance between the mass of the 

 ingesta and that of the egesta. If the energy-values of ingesta 

 and egesta be determined, a difference will be found; that is, 

 the energy-value of the ingesta is greater than that of the egesta. 

 But the difference will be represented by the value of the energy 

 of the mechanical work done by the animal, by the heat con- 

 ducted away from its body by conduction and radiation, and by 

 the heat of the egesta. The animal body is therefore a machine 

 that transforms energy just as a heat-engine does, with the 

 limitation that we have suggested, of the second law of energetics. 



It is a much more " efficient" machine than those of thermo- 

 dynamics, if we like to put the difference in this way. But it 

 is hardly accurate to speak of the efficiency of the organic 

 mechanism in the same way as an engineer speaks of the 

 efficiency of a heat-engine ; for the animal efficiency is an 

 adaptation. The efficiency of an overfed, sedentary man is 

 only a small fraction of the efficiency of a soldier in perfect 

 health and in " hard " training. The fraction of the potential 

 energy of the food which transforms to the kinetic energy of 

 bodily movements obviously depends on the "will" of the 

 animal — it is an adaptation to the circumstances in which the 

 animal places itself. 



There is a certain loss in the transformation of chemical 

 energy into mechanical work in an inorganic system. Some 



1 That is, the organism considered like other physico-chemical systems as 

 an object in space, objectively considered. Subjectively some things — dreams, 

 visions, some memories, hallucinations — are not conserved. We get over this 

 difficulty by saying that the things that are not conserved, though they possess 

 existence, are unreal. The things that are real are the things that are conserved. 



