36 



THE CELL 



Since NaCl plays the most important role in maintaining this pressure, one 

 might suppose that this is the only special physiological significance of common 

 salt. That is not the case however, as appears from the fact that a frog's mus- 

 cle which remains excitable for a long time in a 0.6-per-cent NaCl solution very 

 soon loses its excitability in an isotonic solution of cane sugar (Overtoil). 



2. Naked elementary organisms have the power also of ingesting solid par- 

 ticles. In many cases this takes place in a very simple manner. The ele- 



TC 



YC~, 



E 



V.c 



FIG. 21. A -H, Several successive phases in the life history of an Amoeba, kept under constant 

 observation for three days; /, another individual encysted. 



A, locoinotor phase: the ectoplasm is seen extending to form a pseudopoclium, into which the 

 endoplasm passes; B, a stage in the ingestive phase; fp, a vegetable organism being in- 

 gested; C, a portion of the Amoeba represented in b, after complete ingestion of the food- 

 particle; D, E, successive stages in the assimilative and excretory processes; F, G, H, 

 successive stages in the reproductive process of the same individual. It will be noticed 

 (F) that the nucleus divides first; vc, contractile vacuole; nc, nucleus; ps, pseudopodium; 

 dt, diatom; fp, food particle. 



mentary organism puts out processes, pseudopodia, which apply themselves to 

 the particles of food, then gradually flow around it until it comes to lie 



