PROTOPLASMIC FUNCTION 49 



vation suggests that the granular ameboid mass (unlike the others) is 

 moving, without apparently being disturbed from the outside. Amebse 

 are continually shifting, in fact, with a sort of slow motion character- 

 istic of themselves. If the animal be in water at a temperature lower 

 than 15 C., the movement may not be perceptible except when one 

 repeatedly draws the outlines of the cell at intervals of several minutes 

 and compares the drawings. When this is done, it is at once obvious that 

 the creature changes in shape if not in position. This spontaneous 

 movement of this minute drop of protoplasm is a wondrous thing, but 

 to its wonder we are accustomed, and call it life. The pseudopod (" false 

 foot"), as it is called, may be on a smaller scale and extend only a little 

 way, almost as a point of protoplasm, soon withdrawing again or else 

 remaining, while others, larger or smaller, push out in various places 

 and directions. Several of these may be extending themselves at one 

 time, some large, some small, some dull, some pointed, all of different 

 shapes, some upward, toward the objective point of the microscope so 

 as to be little noticed, the size or bulk of the cell meanwhile not changing, 

 but only its shape. It is evident that a large pseudopod is made always 

 at the expense of some other part of the creature. When the flowing 

 occurs in one direction continually the animal advances, and in this way, 

 hither and thither, it creeps, especially out of open spaces, very slowly 

 and indirectly, over the bottom of the drop in which it lies. (See Move- 

 ment, page 38.) 



The fluidity of the ameba is its most conspicuous property; without 

 it all these curious "ameboid movements" would be impossible. This 

 is true of almost all protoplasm. The mode of this motion in detail is 

 characteristic. With a high-power microscope it may be readily seen 

 that it consists of a curious combination of rolling, streaming, and push- 

 ing particles, the movement of the different parts of the bioplasm being 

 made clear by the metaplasmic granules which are so conspicuous in 

 ameba. This liquid motion is technically known as protoplasmic stream- 

 ing. When stimulated, as by a jarring, the movement ceases and the 

 animal, contracting its pseudopodia, takes a shape more closely approach- 

 ing a sphere than it had before. This shape, however, if the animal be 

 left unstimulated, soon vanishes in the ceaseless pseudopod-making and 

 unmaking just described. 



Patience in observation would show how the ameba gets its food and 

 how it swallows and digests it. The animal appears not to have sense of 

 smell or taste or sight, by which more complex animals may recognize 

 their food at a distance. It has some sort of sense, however, such that 

 on contact with a bit of quartz and then with a bit of nutriment, it will 

 reject the quartz and ingest the food. When in its aimless pseudopodial 

 creeping the animal has come in contact with a particle which it can 

 digest and use as a source of tissue and of energy, the animal at once, 

 but in its characteristically slow way, sets about ingesting it. This is 

 often a difficult task. One side of the particle is surrounded by ,a 

 pseudopod, and if the food does not slip away, another on the oppo- 

 4 



