CHAPTER II. 



THE CBIvIy AND ITS LIFE. 



Probably the most fundamental conception in biology is 

 that of the cellular structure of all animals and plants. The 

 discovery that all living things are made up of separate and 

 individual cells laid the scientific foundation for the sciences 

 of histology and embryology, and very materially modified 

 physiological investigation. It is the bridge that connects 

 plants and animals, and is the key to the proper understand- 

 ing of the phenomena of their growth and development. 

 But such a far-reaching and clarifying conception did not 

 appear suddenly. Our present notions are the result of 

 much investigation and reach back through the observations 

 of many years. The ease and familiarity with which we 

 now speak of cells, of protoplasm, of nucleus, etc., might 

 argue at first sight that we are dealing with a long estab- 

 lished, always-evident bit of knowledge, while as a matter 

 of fact these ideas are even now in the process of formation. 



HISTORICAL VIEW. 



When L,eeuwenhoek, the pioneer in the use of the micro- 

 scope, began to extend human observations with the aid of 

 this added sight a new world was opened, and with avidity, 

 sometimes with mere curiosity, observers subjected all sorts 

 of things to the scrutiny of the microscope. In this way 

 Robert Hooke, of England, 1667, while examining some- 

 what indiscriminately all sorts of things with his rude micro- 

 scope, placed a thin section of ordinary cork under the 

 instrument and noticed that the section contained innumer- 

 able little chambers which, because of this, he called cells. 

 He had, of course, no idea as to the meaning of these cham- 

 bers, but used the term " cell " as we still employ the word 

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