CHAPTER V. 

 THE CELL. 



The most simple living beings consist of single struc- 

 tures, i.e., cells, and are known as protozoa when of 

 animal nature, protophyta, when of vegetable nature. 

 More complex beings are composed of an increasing 

 number of cells which eventually become innumerable. 

 Such are known as metazoa and metaphyta, respectively. 

 An analysis of structure thus leads to the cell as the 

 unit, and before complexly organized beings can be 

 understood a knowledge of cells becomes imperative. 



Until the nineteenth century, microscopy had not 

 reached a point at which it was able to place satisfactory 

 interpretation upon the minute structure of either 

 plants or animals. This came in 1838 when Schleiden, 

 a German botanist, showed that vegetable tissues were 

 composed of various combinations of more or less similar 

 living units formed in a true and orderly manner, and 

 Schwann discovered the same to be true for animals. 



The living vital nature of the structural units 

 formed the basis of Kolliker's new science of histology, 

 became the foundation of a new conception of physiology 

 in the hands of Verworn, and was made the basis of 

 modern pathology by Virchow. 



The term cell came to be applied to the elementary 

 structural units in a peculiar way. In 1665 Robert 

 Hooker, examining a piece of cork with the microscope, 

 found it made up of a large number of minute compart- 

 ments, which reminded him of the cells of a monastery. 

 He, therefore, called each "a cell," and though time has 

 revealed the true nature of the elements, and showed them 

 to be other than closed spaces, the name has survived. 



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