CHAPTER 3 



UNITS OF LIFE— CELLS 



Going back to the story of the origin of 

 hfe, it will be remembered that protoplasm 

 came into being very slowly and its organi- 

 zation into cells must likewise have required 

 a very long time. All cells, from the free- 

 living one-celled Protozoa to the many- 

 celled animals, are extremely complex, and 

 certainly the result of hundreds of millions 

 of years of evolution. All cells perform es- 

 sentially the same functions whether they 

 are deep in the muscles of an elephant or 

 exist as independent individual units like 

 the amoeba. Before we examine the general 

 cell structure more carefully, a little of tlie 

 historical background of cell studies may 

 help us in our perspective of modern sci- 

 ence. 



Long ago, about 1665, an English biolo- 

 gist by the name of Robert Hooke cut thin 

 slices of cork and placed them under his 

 newly fashioned microscope. He noted that 



this material was composed of numerous 

 tiny compartments to which he assigned the 

 name "cells," a name that has come down to 

 the present time. He gave them this appel- 

 lation because they reminded him of the cu- 

 bicles in monasteries in which monks of his 

 time lived. Today any beginning biology 

 student can repeat Hooke's experiment and 

 be rewarded with a much better visual 

 image of cells, although he would probably 

 lack some of the enthusiasm that compelled 

 this inquiring man of the seventeenth cen- 

 tury to make the discovery. 



Everyone who was sufficiently curious 

 to follow the exciting hobby of looking 

 through the newly invented microscope of 

 this early period saw that all parts taken 

 from living things were composed of these 

 tiny "bladders," as Grew called them. Their 

 first and only interest seemed to lie in the 

 fact that animals and plants were made up 



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