NATURE OF LIFE. 3 



d. Mode of Increase. When unorganised bodies increase in 

 size, as crystals do, the increase is produced simply by what is 

 called "accretion;" that is to say, by the addition of fresh 

 particles from the outside. 



Organised bodies increase by what is often called the " in- 

 tussusception " of matter ; in other words, by the reception of 

 matter into their interior and its assimilation there. To this 

 process alone can the term " growth " be properly applied. 



e. Cyclical Change. Unorganised bodies exhibit no actions 

 that are not purely physical or chemical, and they show no 

 tendency to periodical vicissitudes. Organised bodies are pre- 

 eminently distinguished by the tendency which they show to 

 pass through spontaneous and cyclical changes. 



To sum up, all bodies which are composed of an aggrega- 

 tion of diverse but definitely related parts, which have a defi- 

 nite shape, bounded by curved lines and presenting concave 

 and convex surfaces, which increase in size by the intussus- 

 ception of foreign particles, and which pass through certain 

 cyclical changes, are organised; and it is with the study of 

 bodies such as these that Biology is concerned. 



In the foregoing it has been assumed, for the sake of simpli- 

 city, that all living bodies exhibit organisation. It is to be 

 remembered, however, that there are living bodies (e. g. Fora- 

 minifera) to which the term of " organised," as above defined, 

 cannot be applied. Such bodies are living, but they are not 

 organised. In these cases the distinction from dead matter de- 

 pends wholly upon the mode of growth, and upon the presence 

 of vital activity as shown by the occurrence of various periodic 

 changes. 



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, as we have defined it, 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 cause of organisation, or the result of 

 t ? 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 the assumption underlies them all that life is 



