NATURE AND CONDITIONS OF LIFE. 5 



b. Arrangeinent of parts. — Dead bodies, when unmixed, are 

 composed of an aggregation of similar and homogeneous parts 

 which bear no definite and fixed relations to one another. 



Living bodies, on the other hand, are in the great majority 

 of cases composed of dissimilar and heterogeneous parts, 

 the relations of which amongst themselves are more or less 

 definite. In other words, most living bodies are " organ- 

 ised," being composed of separate parts or " organs," which 

 have certain definite functions in the general economy, li 

 must, however, be borne in mind, that organisation, though 

 in the vast proportion of cases a concomitant of vitality, is 

 not necessarily present in living bodies. Some living beings 

 (such as the minute organisms known as the Foraminifera) ex- 

 hibit no distinct parts or organs, and cannot therefore be said 

 to be "organised" in any proper sense of the term, whilst they, 

 nevertheless, exhibit all the essential phenomena of vitality. 



c. Form. — Dead bodies are either of no definite shape — 

 when they are said to be " amorphous "—or they are cr)'s- 

 talline, in which case they are almost invariably bounded 

 by straight lines and plane surfaces. Living bodies are 

 almost always of a definite shape, presenting convex and 

 concave surfaces, and being bounded by curved lines. 

 Some living bodies, however, cannot be said to have any 

 fixed form, but are extremely mutable in figure. In no 

 case, however, could such be confounded with either the 

 amorphous or the crystalline forms of dead matter. 



NATURE AND CONDITIONS OF LIFE. 



Life has been variously defined by different writers. 

 Bichat defines life as " the sum total of the forces which 

 resist death;" Treviranus, as "the constant uniformity of 

 phenomena with diversity of external influences ; " Duges, 

 as "the special activity of organised bodies;" and Beclard, 

 as "organisation in action." All these definitions, how- 

 ever, are more or less objectionable, either because they 

 really express nothing, or because the assumption under- 



