CELLS 43 



Amitotic cell-division is often a means of increasing the 

 nuclear surface in a cell. In many active cells the nucleus 

 becomes very much branched, and it is only a step beyond 

 this to have it break up into pieces. It will be remembered 

 that the nucleus controls synthetic metabolism in the cyto- 

 plasm around it. The cell can build up faster with the in- 

 creased surface brought about by division, just as man can 

 freeze ice cream faster with small pieces of ice than he can 

 with large chunks. 



Cell-division does not take long in some cases from ten 

 minutes to half an hour. Many cells in your body have 

 divided mitotically since you started to read this chapter. 

 As to differences between the two types mitosis is pri- 



Fio. 26. Amitosis, or direct cell division. The nucleus elongates and pinches 

 in two. A membrane is formed between the two new nuclei, thus making two 

 cells. Amitosis is a quick method of increasing nuclear surface. 



marily for the exact division of the chromatin; amitosis is 

 chiefly for increasing the amount of nuclear surface in pro- 

 portion to the cytoplasm. 



THE CELL THEORY 



The modern "cell theory" asserts that cells are the units 

 which build every living organism. No plant or animal 

 exists which does not have the protoplasm divided upon 

 into cells. Though this view is generally accepted by the 

 scientific world, it is less than a hundred years since it was 

 pronounced. 



In 1665 an Englishman named Hooke, when making a 

 careful examination of a piece of bark, discovered that it 

 was made up of little compartments arranged in regular 



