6 MANUAL OF ZOOLOGY. 



b. Cyclical Change. All dead matter tends to assume a 

 condition of permanent stability and repose. Living matter, 

 on the other hand, is pre-eminently distinguished by its ten- 

 dency to pass through a series of cyclical changes, all the 

 actions of living bodies being accompanied by a correspond- 

 ing destruction of the matter by which these actions are 

 effected. All these cyclical changes are effected by the slow 

 but incessant reduction of the living matter of the organism to 

 the non-living condition. Active life, therefore, can only be 

 carried on by the constant destruction of portions of the liv- 

 ing matter of the body ; and to meet the loss thus caused, it 

 is necessary that a corresponding amount of non-living mat- 

 ter should be constantly " assimilated," and raised from the 

 statical condition of dead matter to the dynamical condition 

 of living matter. 



c. Relations to the outside World. Dead bodies are subject 

 to the physical and chemical forces of the universe, and have 

 no power of suspending these forces, or modifying their action, 

 even for a limited period. On the other hand, living bodies, 

 whilst subject to the same forces, are the seat of something in vir- 

 tue of which they can override, suspend, or modify the actions 

 of the physical and chemical forces by which dead bodies are 

 exclusively governed. Dead matter is completely passive, 

 unable to originate motion, and equally unable to arrest it 

 when once originated. Living matter, so long as it is living, 

 is the seat of energy, and can overcome the primary law of the 

 inertia of matter. However humble it may be, and even if 

 permanently rooted to one place, every living body possesses, 

 in some part or other, or at some period of its existence, the 

 power of independent and spontaneous movement a power 

 possessed by nothing that is dead. Similarly, the chemical 

 forces, which work unresisted amongst the particles of dead 

 matter, are in the living organism directed harmoniously to 

 given ends, their action regulated under definite laws, and 

 their natural working often strikingly modified, or even tem- 

 porarily suspended, and this as effectually and as perfectly in 

 the humblest as in the highest of created beings. 



As a result of this, dead bodies exhibit nothing but reactions, 

 and these purely of a physical and chemical nature, whilst they 

 show no tendency to pass through periodical changes of state. 

 On the other hand, living bodies exhibit distinct actions, and 

 are pre-eminently characterised by their tendency to pass 

 through a series of cyclical changes, which follow one another 

 in a regular and determinate sequence. 



