LIVING MATTER 



59 



plant and animal cells. It has been found convenient to stain 

 masses of cells with various kinds of pigments or dyes, to make 

 the structure stand out more distinctly under the microscope. 

 When certain dyes are used, the nucleus becomes particularly 

 distinct, since it absorbs these dyes more readily than do other 

 parts of the cells, and within the nucleus we can sometimes 

 see fine little rods or strands 

 (Fig. 28). 



47. Numbers of cells. Most 

 plants and animals that you 

 have seen probably have in- 

 definite numbers of cells, and 

 these run into countless mil- 

 lions. Some living things, how- 

 ever, have a very definite and 

 limited number of cells. 



Fig. 30. Green slime. ( x 500) 



This plant consists of a single cell. When 

 the cell divides into two, the daughter 

 cells may cling together or they may be 

 separated. Sometimes a cluster, or "col- 

 ony," is formed, containing many cells; 

 in such a cluster each cell is independ- 

 ent of the others, since each is capable 

 of making its own food as well as of 

 absorbing the raw materials from the 

 environment 



One of the simplest animals is 

 the one-celled ameba, which lives 

 in stagnant pools and other wet 

 situations. Under the microscope 

 it appears to be an irregular lump 

 of jellylike matter, in which vari- 

 ous granules and bubbles can be 

 made out. There is a nucleus, and 

 all around it movements are con- 

 stantly taking place. The shape of 



the mass of naked protoplasm is constantly changing, resulting in slug- 

 gish movements of the animal. The slimy mass swallows particles that 

 may serve as food, and it crawls away from contained particles that are 

 no longer of service. The animal is sensitive to physical and chemical 

 forces in the environment, and responds to disturbances by contractions 

 of the protoplasm (Fig. 29). 



In many species of plants each individual consists of a single 

 cell. The bacteria, of which everybody hears a great deal, 

 are one-celled plants. The "green slime," which lives on the 

 shady side of trees or on damp shingles, is another one-celled 

 plant. 



