'48 



ORGANISMS OF ONE CELL 



factors in the development of the multifold structures in the 

 living world. 



Amoeba proteus captures food and draws it into the body 

 protoplasm through the agency of the pseudopodia, or rather, 

 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, 



FIG. 19. Amoeba dividing (A}, ingesting food, and encysted (D). p, 

 Retracted pseudopodium; dt, diatom taken in as food; other letters as in Fig. 18. 

 (From Sedgwick and Wilson after Leidy and Howes.) 



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

 brought about by the secretion of an acid digestive fluid from 

 the surrounding endoplasm. Through the action of this 

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

 killed and then disintegrated. l 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 protein sub- 



1 No enzyme analogous to pepsin and acting in this acid medium is known to 

 occur in Amoeba proteus. 



