The Cell as a Fundamental Unit of Life 



Today it is generally understood that cells are the basic units of 

 living matter, but such a concept has come into general acceptance only 

 in comparatively recent times. Before the days of the modern micro- 

 scopes it was thought that all living things were individual units in 

 themselves without any subdivision into smaller parts. Then, as the 

 primitive microscopes were developed, it gradually became apparent 

 that there were smaller units of organization, in some forms of life at 

 least. To Robert Hooke, an English biologist, goes the credit for early 

 observation and naming of cells. In 1665 he published a book describ- 

 ing the compartmentalized nature of many different forms of living 

 matter he had observed. In particular he described this structure as 

 seen in thin slices of cork. The compartments which he saw reminded 

 him of the cells of a honeycomb in a beehive and he, therefore, sug- 

 gested that they be called "cells." Of course, he saw only the dry, dead 

 cell walls in the cork, for all of the protoplasm had died and was dried 

 up, but the suggested name received general acceptance and we use it 

 today. 



In the course of time the nature of cells became better known ; and 

 finally, in 1839, two German biologists, Schleiden and Schwann, after 

 thorough research on both plant and animal material, formulated the 

 cell theory, which held that all living things are composed of cells. 

 Continued study has shown this theory to be essentially correct, al- 

 though we now know that there are certain very elementary forms of 

 life, such as viruses, that must be excepted from such broad generaliza- 

 tions. Much biological research today is concentrated on the cell, for 

 we realize that the key to many of our complex problems of heredity, 

 growth, reproduction, embryology, and physiology lies within the cell. 

 Before beginning a study of the animals as a whole, therefore, we will 

 spend some time learning something about this smallest unit of animal 

 organization, the cell. 



The Parts of a Cell 



If you wish to see some cells from the human body you can obtain 

 them easily by gently scraping the skin on the inside of your cheek 



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