PROTOPLASM: THE PHYSICAL 

 BASIS OF LIFE 



CHAPTER 2 



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Protoplasm and 



Cellular 



Organization 



What is life? 



This is a question the biologists have been 

 trying to answer for centuries. As a matter 

 of fact, biology may be defined as the sci- 

 ence of life. A fly buzzing about on a win- 

 dow pane is certainly alive, but after it is 

 swatted successfully, it is just as certainly 

 dead; life has departed from it. The most 

 obvious change that has taken place in the 

 fly is the loss of its ability to move and to 

 take in food. It has lost the power to respond 

 in any way to stimuli; for example, we can 

 poke it with a pencil without observing any 

 reaction. Evidently the visible activities of 

 the fly have ceased. As we shall see later, the 

 cessation of visible activities is due to the 

 cessation of activities within the substance 

 of the body. This living substance is known 

 as protoplasm. As long as protoplasm is able 

 to carry on its activities, it is alive; when 

 these activities cease, it is no longer alive. 

 Therefore, life may be studied in terms of 

 the activities of protoplasm. 



Most of our present knowledge of biology 

 is attributable to a century of work on the 

 chemistry and structure of protoplasm. In 

 fact, if we want to know what makes the 

 heart beat, a cell divide, or any other normal 

 function of the body, we seek explanations 

 in terms of the protoplasm that is in all liv- 

 ing cells. Since disease and aging result from 

 changes in the normal activities of proto- 

 plasm, understanding of normal protoplasm 

 is one of the best approaches to understand- 

 ing disease, for diseases are, in the final anal- 

 ysis, problems of protoplasm. 



Physical organization 

 of protoplasm 



The structure of protoplasm cannot be 

 seen with the naked eye, hence we can learn 

 about it only with the aid of a microscope. 

 The amoeba, to be studied later, affords an 

 excellent opportunity to make actual ob- 



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