INTRODUCTION. 



FIG. 1. 



IN examining different objects and substances, we in- 

 stinctively distinguish between inorganic and organic 

 matter. Organic matter presents us with material which 

 has, or once had life, and is of a definite structure. It 

 is made up of one or many units, so-called cells, each of 

 which, though generally of small size, bears the same re- 

 lation to an organism that a tile might bear to a build- 

 ing. On examining several cells from different organisms, 

 as we might examine the tiles from different houses, we 

 find that they resemble one another, in that each is com- 

 posed of a nutritive material, the pro- 

 toplasm (pro'to plazm), which may be 

 inclosed by a thin cell-wall, and may 

 contain an area, the nucleus (nu'kle us), 

 which in turn may present one or more 

 foci, the nucleoli (nu kle'o li). An isolated 

 cell, absorbing food, may grow and sub- 

 divide, each subdivision again subdividing, until a com- 

 plex organism, or broad patches, called tissues, are formed. 

 Organisms are naturally divided into two kingdoms 

 the vegetable and the animal the lower forms of each 

 of which so resemble one another as almost to defy dis- 

 tinction. 



Group of Cells. Cw, Cell- 

 wall. JV, Nucleus, n, 

 NuclS'olus. P, Pro- 

 toplasm. (Greatly en- 

 larged.) 



