AMEBA 



49 



Ameba, we cannot explain ingestion by means of these physical 

 imitations. 



Digestion. Digestion takes place without the aid of a stomach. 

 After a food vacuole has become embedded in the endoplasm 

 its walls pour into it a secretion of some mineral acid, probably 

 HC1. " It is probable that the minute particles of nucleopro- 

 teids that are constantly arising in the neighborhood of the 

 nucleus contain certain digestive ferments which stimulate the 

 formation of the mineral acid in the vicinity of the gastric 

 vacuole " (32, p. 79). The digestive fluid seems to dissolve only 

 proteid substances, having no effect upon fats and carbohydrates. 

 That the nucleus plays an important role in digestive processes 

 was shown by Hofer (36), who found that if a well-fed Ameba was 

 cut in two, the non-nucleated portion was unable to digest food. 



Egestion. Indigestible particles are egested at any point 

 on the surface of the Ameba, there being no special opening to 

 the exterior for this waste matter. Usually such particles are 

 heavier than the protoplasm, and as the animal moves forward 

 they lag behind, finally passing out at the end away from the direc- 

 tion of movement; that is, Ameba flows away, leaving the indi- 

 gestible solids behind. 



Assimilation. The peptones, derived from the digestion of 

 proteid substances, together with the water and mineral matter 

 taken in when the gastric vacuole was formed, are absorbed by 

 the surrounding protoplasm and pass into the body substance of 

 the animal, no circulatory system being present so far as we know. 

 These particles of organic and inorganic matter are then assimi- 

 lated ; that is, they are rearranged to form new particles of liv- 

 ing protoplasm, which are deposited among the previously existing 

 particles. The ability to thus manufacture protoplasm from 

 unorganized matter, it will be remembered, is one of the funda- 

 mental proper ties of living substance (p. 10). 



Dissimilation. The energy for the work done by Ameba comes 

 from the breaking down of complex molecules by oxidation or 

 tf physiological burning." This is known as dissimilation or 



