GENERAL ZOOLOGY 



Electron gun 



Rg. 2.4. Electron microscope. This 

 instrument is almost 8 feet high and 

 weighs about 1400 pounds. Objects 

 with a diameter of only 20 angstrom 

 units can be resolved. Initial mag- 

 nification range is x 1400-30,000; 

 useful photographic enlargements of 

 X 200,000 magnification can be ob- 

 tained. With a magnification of this 

 size, a dime would be more than 2 

 miles in diameter. (Courtesy Radio 

 Corporation of America.) 



Photographic 

 plate here 



separate layers in a centrifuge tube. These layers can then be selectively 

 removed and relatively uniform groups of cell parts obtained. Biochemical 

 techniques are used in an effort to determine the chemical composition of such 

 isolated cell parts and to investigate their function in the life of the cell. 

 Cells and their parts are usually studied as taken from their normal positions 

 in the organs of an animal. However, information about the capabilities 

 of individual cells or groups of them can be increased by growing cells 

 removed from the control of the coordinating mechanisms of the organism. 

 Cells, wherever they are, must have their basic requirements for life satisfied. 

 They must be handled with sterile techniques, so that they are not contami- 

 nated with microorganisms, be able to obtain essential nutrients and oxygen, 

 and be kept moist. They must also be incubated at their normal temperatures 

 and have the waste products of their metabolism removed. When the technique 

 of tissue culture is used, small bits of tissue are removed from an organism 

 and placed in tubes or flasks in which a nutrient solution bathes them as the 

 containers rotate in an incubator. Cells migrate out from the original bit of 



16 



