102 ANIMAL LIFE 



in free oxygen. Plants and lowly animals possess a 

 disruptive faculty, by which they can in the absence of 

 free oxygen break up their store of carbonic gas and 

 set it free. From reserves in seed or muscle fresh 

 energy is obtained by this analytic action. Moreover, 

 in ordinary muscle-breathing the oxygen in the blood 

 is not directly used by the tissue, but is first stored, 

 controlled, and delivered subtly to the muscle, under 

 the pressure of that inward, invisible governor that 

 converts the breath of air into the breath of life. 



Nor, again, is the contrast of economy in vital 

 actions with the waste of fuel a less conspicuous 

 feature of their work than variety or inwardness. 

 The best coal-motors are wasteful, and give out in the 

 desired form of work but one-eighth to one-ninth of the 

 energy imparted, the rest escaping by conduction, in- 

 complete combustion, and other wasteful outlets. 

 Beings are rather more productive and less wasteful. 

 A man given 0*44 kilos of food, representing a million 

 units of energy, gives out in a day, work estimated at 

 one-fifth to one-sixth of this. This economy, unequalled 

 in other carbon-combustions, is due to the central and 

 peripheral control of the nervous system playing upon 

 the fitful external supply, and is signalised in our 

 constant temperature, equable pulse, and regular 

 breathing. 



The quest for oxygen : respiration and evolution. 

 Water contains air, as we see by the bubbles that 

 rise on heating ; but the amount of oxygen is a mere 

 fraction of that contained in an equal volume of the 



