4 INTRODUCTION 



dividual organism is limited. It comes to an end by death and 

 subsequent decay, by division, or by fusion of its body with 

 another similar body. In either case the living individual, as 

 such, ceases to exist. 



11. Crystals are inert, while organisms possess to some degree 

 the power of movement in response to an external stimulus. 



12. Thus we have the material world made up of lifeless, or 

 inorganic bodies, and living, or organic bodies. The following 

 table exhibits in parallel columns the similarities and differences 

 of the two classes of bodies: 



CRYSTALS 



1. Are unorganized. 



2. Grow by accretion (so 

 also hailstones, concretions, 

 stalactites). 



3. Have indefinite shape and 

 plane surfaces. 



4. Size not limited. 



5. Generate spontaneously. 



6. May exist indefinitely. 



7. Are inert. 



ORGANISMS 



1. Are organized. 



2. Grow by assimilation and 

 intussusception. 



3. Have definite shape and 

 curved surfaces. 



4. Size limited. 



5. Develop from a germ. 



6. Have a limited life period. 



7. Have power of motion. 



THE LIVING SUSBSTANCE 



13. All the activities of an organism, by which it is distin- 

 guished from inorganic bodies, are the activities of the living 

 substance, which is called protoplasm. But not all of the sub- 

 stance of an organism is protoplasm. Besides the protoplasm 

 there is usually more or less inert substance which was formed 

 by the protoplasm, but which does not of itself possess life. 

 Of such substances are the hard parts of bones and the super- 

 ficial layers of the skin, the corky layers of bark and the hard 

 fibres of wood, etc. This inert substance may be wholly want- 

 ing, or it may constitute the larger part of the body of the 

 organism. 



