660 EVENING DISCOURSE. 



dynamics, restricts the direction of energy transformations. Thus a large tank of 

 hot water at an even temperature will not he found to cool itself and the disappearing 

 heat energy to appear as the kinetic energy of a revolving fly-wheel or as the increased 

 potential energy of a raised mass of metal, no other changes of any sort having 

 taken place. Such a transformation need not, however, in any way conflict 

 with the Law of Conservation. Unco-ordinated energy in statistical equilibrium, 

 i.e. of even potential, does not spontaneously transform itself into co-ordinated 

 energy. Now it would be a discovery of tremendous importance if plants or animals 

 were found to be exceptions to this rule. But, so far as is known, the facts of biology 

 and physiology seem to show that living beings, just like inanimate things, conform 

 to the Second Law. They do not live and act in an environment which is in perfect 

 physical and chemical equilibrium. It is the non-equilibrium, the free or available 

 energy of the environment which is the sole source of their life and activity. A steam 

 engine moves and does work because the coal and oxygen are not in equilibrium, 

 just as an animal lives and acts because its food and oxygen are not in equilibrium. 

 As Bayliss has so finely put it, equilibrium is death. The chief source of life and 

 activity on this planet arises from the fact that the cool surface of the earth is constantly 

 bathed in a flood of high temperature light. If radiation in thermal equilibrium with 

 the average temperature of the earth's crust were the only radiant energy present, 

 practically all life as we know it would cease, for then the chlorophyll of the green 

 plants would cease to assimilate carbonic acid and convert it into sugar and starch. 

 The photo-chemical assimilation of the green plant is a fact of supreme importance 

 in the economy of life. This transformation of carbonic acid and water into starch 

 and oxygen represents an increase of free energy, since the starch and oxygen tend 

 naturally to react together and give carbonic acid and water. Such an increase in 

 free energy would be impossible if there existed no compensating running-down or 

 degradation of energy. But this running-down or fall in potential is provided by the 

 difference in temperature between the surface of the sun and the surface of the earth, 

 a difierence of some five or six thousand degrees. All living things live and act by 

 utilising some form of non-equilibrium or free energy in their environment. The living 

 cell acts as an energy transformer, running some of the free energy of its environment 

 down to a lower level of potential and simultaneously building some up to a higher 

 level of potential. The nitrifying bacteria investigated by Winogradsky and recently 

 by Meyerhof utilise the free energy of ammonia plus oxygen. By burning the ammonia 

 to nitrous or nitric acid they are enabled to assimilate carbonic acid and convert it 

 into sugar or protein. Other bacteria utilise the free energy of sulphuretted hydrogen, 

 plus oxygen. Fungi and anferobic bacteria utilise the free energy available when, 

 complex organic compounds pass into simpler chemical compounds. The close study 

 of these energy exchanges and transformations is becoming a very important branch 

 of cellular physiology, and in the hands of Warburg and Meyerhof in Germany and 

 of A. V. Hill in England — to mention only a few eminent names — has already yielded 

 results of the greatest value and importance. It would be a great thing if one of 

 these investigators were to find a case where the Second Law of Thermodynamics 

 broke down. Up to the present, however, it appears that all these energy trans- 

 formations of the living cell conform with the Second Law as it applies to the inanimate 

 world. Thus another part of the apparent freedom or spontaneity of life, of which 

 I spoke before, disappears. A living being is not a magical source of free energy 

 or spontaneous action. Its life and activity are ruled and controlled by the amount 

 and nature of the free energy, the physical or chemical non-equilibrium, in its 

 immediate environment, and it lives and acts by virtue of this. The cells of a human 

 brain continue to act because the blood stream brings to them chemical free energy 

 in the form of sugar and oxygen. Stop the stream for a second and consciousness 

 vanishes. Without that sugar and oxygen there could be no thought, no sweet 

 sonnets of a Shakespeare, no joy and no sorrow. 



To say, however, that the tide of life ebbs and flows within the limits fixed 

 by the laws of energy, and that living beings are in this respect no higher and 

 no lower than the dead things around us is not to resolve the mystery. 

 Consider for a moment a few of the phenomena exhibited by living things. 

 The fertilisation of the ovum, the growth of the embryo, the growth of the complete 

 individual, the harmonious organisation of the individual, the phenomena of 

 inheritance, of memory, of adaptation, of evolution. Viewing these phenomena 

 in the light of the facts known to physics and chemistry, it is little wonder 

 that some modem philosophers have followed in the stejis of certain older ones and 



