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 cell was originally conceived to be an anatomical 

 unit, and it was supposed that all cells presented more 

 or less uniformity of structure; but it is now known that 

 their structures may be quite dissimilar. Indeed, this 

 dissimilarity of structure admits such latitude into the 

 concept "cell" that it becomes almost impossible to 

 define it. As here used, the term cell signifies a struc- 



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