THE BIOLOGICAL UNIT 43 



ing wall. It streams, now in this direction, now 

 in that, but always under the ameba's control. If, 

 by any chance, one presses too heavily upon this 

 delicate organism, the life of the ameba is de- 

 stroyed and the protoplasm begins to mix freely 

 with the water. In two or three minutes the body 

 of the ameba becomes unrecognizable. One has 

 the same difficulty in trying to describe what was 

 destroyed in the ameba as in man. A beginning 

 student can tell whether an ameba is dead or 

 alive, while the ablest philosopher or scientist can- 

 not tell what the ameba lost when accidently 

 crushed. 



The life thus seen to center in a microscopic 

 ameba is similar in all essential details to the life 

 in man: every fundamental fact associated with 

 the biological units in man is present in an ameba. 

 It is true that man does not contain in his body 

 any cell that can carry on as many vital processes 

 as does the ameba, but it is also true that the 

 ameba cannot move as quickly, transmit stimulus 

 as rapidly, nor protect itself as effectively as does 

 man. Generalized ameba is not as efficient as 

 specialized man. 



The second type of biological unit existing 

 within the limits of a single cell which we will 

 consider, are bacteria. All bacteria are plants 

 but they are but one of many plants that live in a 



