Life of Plants and Animals 197 



than that these single cells are capable of leading an 

 independent existence, of moving, assimilating, grow- 

 ing, responding to stimuli, and multiplying by division. 

 They apparently select their own food, seem to avoid 

 danger, recognize their own kind, and enjoy the power 

 of spontaneous action. Without any evident external 

 cause they are able to arrest motion, to start again, 

 to turn to the right or to the left or to wheel com- 

 pletely about, retracing their steps. No one observing 

 the actions of one of these organisms could fail to 

 be impressed with its apparent intelligence. In fact, 

 this protoplasm moves without muscles, feeds without 

 a mouth or a stomach, and, shall we say, perceives, 

 thinks, wills, and knows without sense-organs or 

 without brains. Inasmuch as these various functions 

 have no corresponding organ, we must conclude that 

 they are various forms of protoplasmic activity. 



All these forms of protoplasmic activity are the 

 result of dissociation of complex organic molecules, 

 a breaking-up of complex substances into more stable 

 inorganic compounds, by which the necessary energy 

 is liberated. Such waste of energy must be made good 

 by the taking in of food, for even protoplasm cannot 

 create energy. When the food supply is exhausted, 

 therefore, when the algi put into the jar have been 

 disorganized and their substance used up by the 

 microbes, these necessarily die from starvation, and 

 the water, which at first became foul and turbid, gradu- 

 ally becomes clear, the organisms having themselves 

 been disorganized into a sediment of dead matter. 

 If more food is supplied the organisms continue to 

 live and multiply indefinitely. The waste resulting 

 from metabolism of the protoplasm is excreted by 

 the cell through the outer cuticle, and oxygen, the imme- 

 diate cause of this metabolism, is taken in in the same 

 way from the surrounding medium. Hence these or- 



