FOOD-TAKING BY AMOEBA 



47 



the protoplasm of the organism streams into pseudopodia 

 around the prey, thus engulfing it (Fig. 19). Some water is 

 engulfed with the food particle and this forms the chief portion 

 of the liquid of the gastric vacuole. This water usually is 

 alkaline in reaction when taken into the body; soon, however, 

 it changes in reaction from alkaline to acid, the change being 

 brought about by the secretion of digestive ferments from the 

 surrounding endoplasm. Through the action of this mineral 



FIG. 19. Amoeba dividing, ingesting food, and encysted. p t Retracted pseudo- 

 podium; dt, diatom taken in as food; other letters as in Fig. 18. (From Sedg- 

 wick and Wilson after Leidy and Howes.) 



acid (supposed to be HC1), the food particle, if living, is first 

 killed and then disintegrated. Later the reaction of the con- 

 tents of the vacuole again changes from acid back to alkaline and 

 in this medium the further processes of digestion are accom- 

 plished. The end result of this series of chemical actions on the 

 food is the formation of proteoses from the proteid sub- 

 stances which, as soluble materials, are then taken into the 

 body protoplasm of the organism; the food particles are said 

 to be digested. 



When the proteid food is thus digested it is only prepared for 



