4 MANUAL OF ZOOLOGY. 



are developed into the likeness of the parent. 4. The matter 

 of a living body is subject to the same physical and chemical 

 forces as those which affect dead matter ; but it is further the 

 seat of something in virtue of which the living body can over- 

 ride the physical laws which control all dead matter. The 

 living body is the seat of energy, and can overcome the pri- 

 mary law of the inertia of matter. It has certain relations 

 with the outer world other than those of mere passivity. 

 However humble it may be, and even if it be permanently 

 rooted to one place, some part or other of every living body 

 possesses the power of spontaneous and independent move- 

 ment a power possessed by nothing that is dead. Living 

 bodies, in short, possess the power of controlling and directing, 

 and to some extent suspending, the action of the physical forces 

 of the universe. 



3. NATURE OF LIFE. 



We have next to determine and the question is one of 

 great difficulty what connection exists between organisation 

 and life. Is organisation essential to the manifestation of life, 

 or can vital phenomena be exhibited by any body which is 

 devoid of an organised structure ? In other words, is life the 

 catftTVf- organisation, or the result of it ? And first, what do 

 we mean by life ? 



Life has been variously defined by different writers. Bichat 

 defines it as " the sum total of the functions which resist death ; " 

 Treviranus, as " the constant uniformity of phenomena with 

 diversity of external influences ; " Duges, as " the special acti- 

 vity of organised bodies ; " and Beclard, as " organisation in 

 action." All these definitions, however, are more or less objec- 

 tionable, since they either really mean nothing, or the assump- 

 tion underlies them that life is inseparably connected with 

 organisation. In point of fact, no rigid definition of life 

 appears to be at present possible, and it is best to regard it as 

 being simply a tendency exhibited by certain forms of matter, 

 under certain conditions, to pass through a series of changes 

 in a more or less definite and determinate sequence. 



As regards the connection between life and organisation, 

 it appears that whilst all organised bodies exhibit this ten- 

 dency to change, and are therefore alive, all living beings are 

 not necessarily organised. Many of the lowest forms of life 

 (such as the Foraminifera amongst the Protozoa) fail to fulfil one 

 of the most essential conditions of organisation, being devoid 

 of definite parts or organs of any kind. Nevertheless, they 



