Biologists Study Animals and Plants 



Fig. io The 7nan is using an 

 electron 7/ncroscope. With 

 its use it is possible to obtain 

 photographs 200,000 times as 

 large as the objects. Yon can 

 see that the electron micro- 

 scope bears no resemblance 

 to the compound micro- 

 scope, (r.c.a.) 



II 



a little world of wriggling, squirming 

 creatures never before seen by man. 

 When he reported his discovery, men 

 in other countries used their lenses to 

 examine similar drops of water. They, 

 too, saw these living things that had 

 been invisible until then. They studied 

 them, filled notebooks with descriptions 

 of their activities, and drew careful dia- 

 grams to illustrate their structures. 



The biologist improves his tools. As 

 microscopes were improved, smaller 

 and smaller living things were found 

 and examined. Today, good microscopes 

 enable us to study objects so tiny that 

 50,000 of them laid end to end would 

 measure only one inch. But increase in 

 magnifying power has not been the 

 only advance. More important than that 



has been the increase in clearness of 

 vision. 



Modern microscopes are impressive 

 instruments of shiny enamel and polished 

 chromium but improvement in appear- 

 ance is much less important than the 

 improvements in the lenses. They are 

 marvels of fine grinding, far, far better 

 than any in the early microscopes. 

 Modern instruments are unlike the 

 early ones in another way; they magnify 

 twice, by two sets of lenses. They are 

 therefore called compound microscopes. 

 The two magnifications are multiplied. 

 If the lens near the object magnifies fifty 

 times and the lens near the eye ten 

 times, the total magnification is 500. The 

 microscope that biologists or physicians 

 use can generally magnify 1 800 times. 



