ON THE NATURE OF LIFE 219 



carbohydrates, and proteids) do not, in general, accumulate, 

 since they are destroyed by bacteria, when they transform 

 chemically into mineral compounds, which again become avail- 

 able as the foodstuffs of plants. 



Evidently, then (and the thesis could be supported to a much 

 greater degree than our limits of space allow), the general 

 tendency of life upon the earth is towards the accumulation of 

 available energy in the form of chemical compounds of high 

 calorific value. The process is restricted mainly by animal and 

 bacterial life, and by the paucity on the earth of mineral 

 nitrogenous compounds. But it is clear that on a lifeless planet 

 the enormous store of available energy contained in the incident 

 solar radiation would at once be dissipated, whereas on one which 

 is the seat of life the energy so received tends to be accumulated. 



The feral animal, as a rule, disappears and leaves no addition 

 to the earth's store of available energy, except in the somewhat 

 rare cases where its tissues become partially converted into 

 bituminous substances. Of all the myriads of animals that have 

 existed on the earth in past geological times, this remains — here 

 and there some oily or bituminous shales and other rocks, and 

 for the rest " ashes and a skeleton and a name, or not even a 

 name." Throughout their lifetimes the chemical energy taken 

 into the bodies of these animals in the shape of foodstuffs has 

 been, in the main, transformed into mechanical energy, which 

 dissipates into heat that becomes radiated away into space. 

 Some of it goes to form the bodies of new individuals which reach 

 maturity, and then cease to grow, but the fraction which is 

 absorbed in reproductive processes (and therefore adds to the 

 mass of animal life, or accumulated available energy) is much 

 smaller than it is among plant organisms. Two tendencies 

 restrict this accumulation in the animal kingdom: (1) Death and 

 putrefactive decomposition by bacteria; and (2) the greater 

 mobility of animals, which carries with it dissipation of energy. 

 The former, however, do not seem to be inevitable processes, for 

 death is something that might have been averted (and is, indeed, 

 averted in the case of certain protozoa), while conditions in which 

 putrefactive decomposition need not occur are easily conceivable, 

 and may, indeed, be realised. 



The tendencies of vegetable metabolism, therefore, make for the 



. accumulation of available energy, but the opposite is the case 



with animal metabolism. Now this is mainly because the 



