C and /), different views of the 

 microscope used by Antony van 

 Leeuwenhoek (cf. p. 140) about 

 1673. A, the compound micro- 

 scope used bv Robert Hooke 

 (cf. p. 11) about 1665, show- 

 ing; method of illumination. 

 (C, D, and E, from W. B. 

 Carpenter, The Microscope and 

 Its Revelations, copyright 1891 

 by J. and A. Churchill, re- 

 printed by permission.) 



AND ACTIVITIES OF CELLS 



and rework it to satisfy his own needs. The more highly organized animals 

 have organs which are responsible for digesting their food, for obtaining their 

 oxygen, for eliminating undesirable materials, for transferring substances from 

 one part of the body to another, and for integrating all the activities of the 

 body. An understanding of these functions rests on an understanding of the 

 cells that make up the tissues and organs. In this chapter we are going to 

 discuss the structure and activities that cells of all animals, whether simple or 

 complex, have in common. 



The Cell Theory 



The discovery of cells was made possible by the use of the microscope, 

 which was invented about 1591 but was not utilized in scientific studies until 

 about 1650. Robert Hooke, one of the early English microscopists, discovered 



11 



