CHAPTER III 

 CELLS AND THEIR ASSOCIATION 



We can imagine a giant of enormous stature and a 

 curious turn of mind who might walk about the earth 

 looking down upon the buildings which men have made 

 as we look at the pebbles in our path. For such a giant 

 a brick house might appear as an object with uniformly 

 red surfaces; the white lines of the mortar might easily 

 be too fine for his vision. He could not observe the fact 

 that the walls of the house are made of individual bricks. 

 This might be revealed to the colossus if he were provided 

 with a microscope of suitable proportions. 



Man has had an experience not unlike that which has 

 just been suggested. Through centuries of eager in- 

 tellectual life he could not see that the green surface of a 

 leaf is a mosaic of minute units. He could not re- 

 solve the substance of an animal body into its con- 

 stituent parts. The modern microscope had to be 

 perfected before this knowledge could be compassed. 

 More than two hundred and fifty years ago there were 

 drawings and descriptions of the appearance of parts 

 of plants and animals under high magnification. Some 

 of these were surprisingly accurate. But the lenses 

 available in the seventeenth century were poor affairs 

 which blurred and distorted the images which they 

 formed. The investigator had to make the best of 

 these faulty aids and, in addition, to ignore so far as he 

 could the fringes of rainbow colors which bordered every 

 object of his study. 



Great improvements in lenses were made about the 

 year 1830, and biologists hastened to employ the new 

 instruments. A fruitful period of research and publica- 



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