PHENOMENA OF LIFE 



II 



caying matter. In a general way we may say that the structure 

 and habitat of any animal limits its size. 



(2) Form. The various species of animals have character- 

 istic forms by which they may as a rule be recognized. Many 

 organisms are extremely irregular in form; for example, sponges 

 incrust the surfaces of rocks or piles in an infinite variety of 

 shapes, and no two trees of the same kind have a similar set of 

 branches, yet every species has certain distinct peculiarities. A 

 person who is familiar with sponges is able to recognize the differ- 

 ent species at a glance, and any one can distinguish an oak from a 

 poplar as far as he can see them. 



Non-living bodies in most cases have no regularity of shape. A 

 piece of granite may form a slab or a boulder or assume any other 

 contour; the water in a lake conforms to the shape of the lake-bed. 



(3) Chemical Composition. If a sufficient variety of inor- 

 ganic bodies are collected and analyzed, every one of the eighty 

 or more chemical elements known to science will be represented. 

 If, on the other hand, any number of living organisms are col- 

 lected, generally not more than twelve elements can be secured 

 by analysis. Furthermore, only five of these will usually be 

 represented in considerable quantities. Thus a typical animal 

 would be found to contain the following elements: 



Carbon 



Oxygen 



Nitrogen 



Hydrogen 



Sulphur 



Phosphorus 



Chlorine 



Potassium 



Sodium 



Magnesium 



Calcium 



Iron 



99 per cent of weight ; 



i per cent of weight. 



