62 



ORGANISMS OF ONE CELL 



ess of digestion begins, as in Amoeba, by the secretion of 

 a mineral acid. The bacteria are killed by this acid and be- 

 gin to swell preparatory to dissolution. After from 10 to 15 

 minutes the vacuoles show an alkaline reaction and the further 

 processes of digestion, requiring several hours, are completed 

 in this alkaline medium. In well-fed Paramecia the cell be- 

 comes loaded with these vacuoles containing bacteria in various 

 stages of digestion. Finally the liquid of the vacuole disappears 

 and the digested food becomes intimately mixed with the pro- 



FIG. 27. Paramecium caudatum in the condition of depression and recovery 

 through the use of salts. 



toplasm and assimilation, presumably as in Amoeba proteus, 

 takes place. 



An instructive picture of the protoplasm of Paramecium can 

 be obtained by systematically over feeding them for a long 

 period, e.g., for some months on a rich hay infusion diet. The 

 protoplasm becomes filled with dark granules, the vacuoles of 

 the protoplasm become indistinct or lost, the contractile vacu- 

 oles lose their rhythmic action and movements are slow and 

 irregular. At such a time the organism is said to be in a state 

 of depression. It is loaded down with reserves of food partly 

 digested and seems to be unable to assimilate (Fig. 27). If a 



