32 



Life: Its Nature and Origin 



Fig. 12. The stages of mitosis shown diagrammatically. For explanation of 

 stages see text. (After Mazia. ) 



stance glutathione, disulphide bridges which originally connected 

 parts of the same protein molecule are switched around to connect 

 adjacent molecules. 



The phenomena of cell growth, spindle formation, and division 

 are visible manifestations of a scries of highly complex chemical 

 reactions occurring in the cell. However, the sum of these reactions 

 requires both raw materials and energy which must be present in 

 the environment of the cells and which must be in such states that 

 the cell can absorb them. These ingested raw materials are the 

 nutrients of the cell. Nutrient material passes through the cell 



