32 Animal Life and Intelligence. 



of its cells, consciousness and the mind-element emerges ; 

 of which we need only notice here that it belongs to a 

 wholly different order of being from the physical activities 

 and products with which we are at present concerned. 



No analogies between mechanical contrivances and 

 organic processes can be pushed very far. To liken the 

 organic cell to a gas-engine is better than to liken the 

 organism to a steam-engine, because it serves to indicate 

 the fact that the fuel does not simply combine with the 

 oxygen in combustion, but that an unstable or explosive 

 combination of " fuel " and oxygen is first formed ; and 

 again, because the effect of this is direct, and not through 

 the intervention of any substance to which the combustion 

 merely supplies the necessary heat. But beyond the fact 

 that a kind of explosive is formed which, like a fulminating 

 compound, can be fired by a touch, there is no very close 

 analogy to be drawn. Nor must we press the explosion 

 analogy too far. The essential thing would seem to be 

 this which, perhaps, the analogy may have served to 

 lead up to that the vital protoplasmic network of the 

 cell has the power of building up complex and unstable 

 chemical compounds, which are probably stored in the 

 plasm within the spaces between the threads of the net- 

 work; and that these unstable compounds, under the 

 influence of a stimulus (or, possibly, sometimes sponta- 

 neously) break down into simpler and more stable com- 

 pounds.* In the case of muscle-cells, this latter change 

 is accompanied by an alteration in length of the fibres 

 and consequent movements in the organism, the products 

 of the disruptive change being useless or harmful, and 

 being, therefore, got rid of as soon as possible. But very 



* It will be well here to introduce the technical terms for these changes. 

 The general term for chemical actions occurring in the tissues of a living 

 creature is metabolism ; where the change is of such a nature that complex 

 and unstable compounds are built up and stored for a while, it is called 

 anabolim; where complex unstable compounds break up into less complex 

 and relatively stable compounds, the term katabolism is applied. We shall 

 peak of anabolic changes as constructive ; katabolic, aa disruptive, or some- 

 times, expletive. 



