20 



THE MICROSCOPE 



had said that blood moved through the body in a circuit and that 

 the beating of the heart supphed the propelhng force. He had 

 no microscope, but reasoned this out from observations made from 

 his dissections. Leeuwenhoek ground a lens to obtain proper 

 magnification, placed a tadpole in a glass tube, and adjusted the 

 tube in front of the fixed lens. When he looked through the lens, 

 he saw the blood, in the tail of the tadpole, come down one blood 

 vessel, cross to another, and return through still another. Thus, 

 by means of his lenses, he proved Harvey's reasoning was correct 

 in the specimen that he w^as studying. Leeuwenhoek did a great 

 deal to stimulate interest in perfecting the microscope. In his 

 day, for each new specimen studied a new lens had to be ground 

 and the object permanently fixed in relation to this magnifier. 

 To-day, microscopes are constructed quite differently. The lenses 

 are permanently mounted in relation to each other, forming 



-•■•'/ • 



Goncocve 

 "1,^X13 



Von Leeuwenhoek. 



One of his many microscopes. 

 What he said: 



What he saw. 



"In the year 1675 I discover'd living creatures in Rain water which had stood but a few 

 days in a new earthen pot, glazed blew within. When these living Atoms did move they put 

 forth two little horns, continually moving themselves. They had a tayl, near four times the 

 length of the whole body, of the thickness (by my Microscope) of a Spider web; at the end 

 of which appeared a globul." 



a compound microscope. We simply change the slides on which 

 the specimens are mounted. Many improvements have been made 

 in microscopes since the time of Von Leeuwenhoek, and the com- 



