46 AN INTRODUCTION TO ZOOLOGY 



Ameba by means of inorganic substances, in an endeavor to dis< 

 cover the physical or chemical nature of its locomotion (40). 

 Even when an apparently reliable imitation is produced, we can- 

 not be certain that the forces at work are actually those which 

 cause the movements of Ameba. Practically all of the imitations 

 thus far reported depend on surface tension. 



One method of producing ameboid movements is as follows 

 (26). A large drop of mercury is placed in a flat-bottomed watch 

 glass and covered with 10 per cent nitric acid. A piece of po- 

 tassium bichromate when placed near the mercury produces a 

 solution which causes local lowering of the surface tension of 

 the drop, and results in the formation of projections and move- 

 ment of the mercury in various directions. 



Metabolism. The various metabolic activities of animals 

 were discussed in Chapter II, pages 13 to 15. In Ameba these 

 processes are seen in their simplest form, and will, therefore, be 

 considered in some detail in spite of the danger of repetition. 

 The entire series of processes connected with the manufacture 

 and destruction of protoplasm are the ingestion of food, diges- 

 tion, egestion, absorption, circulation, assimilation, dissimila- 

 tion, secretion, excretion, and respiration. 



Food. The food of Ameba consists of very small aquatic 

 plants such as Oscillaria, and diatoms, Protozoa, bacteria, and 

 other animal and vegetable matter. A certain amount of choice 

 of food is exercised, or its body would become overloaded with 

 particles of sand and other indigestible material among which it 

 lives. Furthermore, it seems to evince a preference for diatoms 

 which one would think too large for easy consumption. This 

 apparent choice of food may be due to ordinary physical laws of 

 fluids. 



Ingestion. The ingestion, or taking in of food, occurs with- 

 out the aid of a mouth. Food may be engulfed at any point on 

 the surface of the body, but it is usually taken in at what may 

 be called the temporary anterior end, that is, the part of the body 

 toward the direction of locomotion. Jennings describes inges- 



