CHAPTER IX 



RECENT CYTOLOGY 



EVERY living creature may be regarded as being built 

 up of a number of structural units which are known 

 as cells. In the case of some of the simplest animals 

 and plants, indeed, the whole body of the organism is 

 composed of a single cell a small mass of living proto- 

 plasm, containing, as a rule, only one nucleus. But 

 in all the higher animals and plants the adult body is 

 made up of a great number of such cells living in 

 intimate association with one another. 



The living material of which the cell is composed is 

 known as protoplasm. Protoplasm is a highly com- 

 plicated and unstable combination of substances, 

 amongst the constituents of which the chemical 

 elements, carbon, oxygen, hydrogen, nitrogen, and 

 sulphur, play the chief parts. Its consistency is slimy 

 and semifluid. 



Concerning the nucleus the most essential and 

 characteristic of cell organs more will have to be said 

 later on. Other important organs of cells are a wall 

 or membrane which externally surrounds them, one 

 or more vacuoles or cavities containing a watery fluid, 

 or sometimes a gas, and a certain number of more solid 



