16 PROTOZOANS. 



an almost structureless and colorless substance, in chemi- 

 cal composition much like the albumen of an egg. It is 

 the physical basis of life. Neither animal nor vegetable 

 life is known to exist apart from it. It is everywhere 

 present in the growing parts of animals and plants. It is 

 capable, as life's agent, of producing the most complex 

 structures. The nucleus within the amoeba is but a bit 

 of the protoplasm of slightly firmer consistency than the 

 rest ; but it is, perhaps, the most essential part. 



Simple as the amoeba is, and wanting in parts, it yet 

 leads an animal life, and exercises all the essential animal 

 functions. 



I. Nutrition. That the amoeba takes food has been seen 

 already. Having neither mouth nor stomach, it ingests and 

 digests its food at the most convenient point. Its proper 

 food consists of the smallest microscopic plants. These, 

 when found within the body of a living amoeba, may, by 

 continued watching, be seen to dissolve away as they are 

 digested. The small amount of mineral food and the 

 larger amount of oxygen necessary for the amoeba are 

 already in solution in the water in which it lives, and 

 need but to be absorbed. These dissolved foods penetrate 

 freely to every part of the protoplasmic mass, and by a 

 process called assimilation they are incorporated into it, 

 and become a part of it. But this process means more 

 than the mere storing of digested food : it means that the 

 food is built up into complex chemical compounds, like 

 those which are the constituents of protoplasm, and that 

 it then becomes a part of the protoplasm, like any other 

 part, in all its properties. The necessary result of this 

 process is that the animal grows. 



But this process also makes possible the animal's activi- 

 ties. The complex chemical compounds formed in this 

 constructive process are highly charged with potential 

 energy and are very unstable, like a single tier of bricks 



