IS THE ORGANISM A MECHANISM? 657 



fraction of this energy is dissipated as heat; a large fraction 

 in the case of a heat-engine, and a smaller fraction in the case 

 where chemical energy transforms directly to electrical energy, 

 and then the latter to mechanical energy. We cannot, however, 

 be quite sure that any part of the potential energy of the food is 

 so dissipated in the metabolism of the perfectly health}' animal. 

 Heat is certainly radiated away from the bod}'' of a mammal, 

 but we must regard heat-production as a definite, purposeful 

 activity in such an organism. It maintains its body at a certain 

 constant temperature, which is that temperature at which its 

 metabolism proceeds with the greatest advantage to itself. The 

 organic system, like the inorganic one, conforms to van't HofFs 

 law, and it is obviously an advantage that the rate of chemical 

 change should be independent of the temperature of the environ- 

 ment. Constant bodily temperature is therefore a compensatory 

 adaptation. The warm-blooded animal is, however, the ex- 

 ception, for the majority are cold-blooded ; that is, their 

 temperature is identical with, or approximates very closely to, 

 that of their immediate environment. In such animals the 

 potential energy of the compounds taken as food transforms 

 into the kinetic energy of the movements of the body without 

 passing through the form of heat. Further, since it is very 

 difficult, or impossible to demonstrate by exact calorimetric 

 experiments, any heat production in a cold-blooded animal, we 

 cannot say that energy is dissipated in its transformations. - 



In disease, or in imperfect functioning, there is, of course, 

 more or less wasteful heat production. But we cannot demon- 

 strate that there is an inevitable, fairly large dissipation of 

 energy in the organic system, and so we cannot apply to it the 

 second law of thermodynamics with all the strictness in which 

 it applies to inorganic systems. Certainly it is misleading to 

 compare the " animal machine " with the heat-engines of physics. 

 The animal organism is a system in which energy falls from 

 a state of high, to a state of low potential, as in, say, the Carnot 

 engine. Some part of the energy of the heat-engine transforms 

 to mechanical energy — does work against resistance — and some 

 part is dissipated and becomes unavailable. In the animal, also, 

 potential energy transforms to mechanical energy, but it certainly 

 has not been shown that any large part of the potential energy 

 taken in becomes truly dissipated, in the cold-blooded animal 

 at all events. 



