ENERGY CHANGES IN ORGANISMS 481 



ence between the slow burning which takes place in the body and any 

 burning which takes place outside it seems to be very perfect when one 

 considers several facts. Food and fuel are both converted into simpler 

 chemical substances, and during this conversion a certain amount of 

 potential energy is liberated as free energy, chiefly as heat and light. In 

 both cases carbon dioxide and water are formed, and in both cases the 

 unburned residue remains, forming the ashes of the fire or the feces passed 

 out of the body. Chemical changes taking place outside the body liberate 

 the same amount of energy as when these changes take place within the 

 body, but the conditions within the body determine the speed of libera- 

 tion and the manner in which the energy is expended. 



498. Organism Compared to an Engine. — In certain respects the 

 comparison between the body and the fire is inadequate. The fire 

 liberates kinetic energy but this kinetic energy can be controlled and 

 directed only in case there is added to the fire some form of apparatus by 

 means of which this control is possible. Such an apparatus is an engine. 

 The body may, therefore, be compared to the fire plus the engine which 

 utilizes the energy and directs its expenditure. As a result of this 

 control the organism is capable of doing a large amount of effective 

 mechanical work. 



499. Organism More Than a Machine. — An organism, though it may 

 be compared to an engine, is, however, far more than any inorganic 

 machine for the following reasons: 



1. It possesses control from within. It is true that living organisms 

 are constantly stimulated and caused to act by various forces in the 

 environment, but it also seems to be true that the very organization of 

 living matter, unstable as it is and prone to change, makes possible 

 activities which are initiated from within the organism without any 

 immediate stimulus from the outside. 



2. It exhibits a degree of harmonious activity between structures 

 which exceeds that shown by any nonliving assemblage of parts. 



3. It has the capacity to regenerate itself. Changes taking place in 

 inorganic masses lead to disintegration and are permanent unless the 

 masses are again acted upon by an outside agent. 



4. It has the power of reproduction, which implies the development of 

 new individuals like the parent. 



5. It possesses individuality, and this individuality is capable of 

 being transmitted from parent to offspring through many generations. 



500. Individuality. — Individuality, as has been indicated in a previous 

 chapter (Sec. 464), is universal among animals. In reference to man it is 

 what we call personality. Its source is in minute differences in the precise 

 character of the organization and, therefore, in the exact functioning 

 of the organism. It involves distinctions which we recognize as existing 



