4 THE PHENOMENA OF LIFE 



The remarkable movement of pigment granules observed in the branched 

 pigment cells of the frog's skin by Lister are also probably due to ameboid 

 movement. These granules are seen at one time distributed uniformly through 

 the body and branched processes of the cell, while at another time they collect 

 in the central mass leaving the branches quite colorless. 



This movement within the pigment cells might also be considered an ex- 

 ample of the so-called streaming movement not infrequently seen in certain 

 of the protozoa, in which the mass of protoplasm extends long and fine pro- 

 cesses, themselves very little movable, but upon the surface of which freely 

 moving or streaming granules are seen. A gliding movement has also been 

 noticed in certain animal cells; the motile part of the cell being composed of 

 protoplasm bounding a central and more compact mass. By means of the 

 free movement of this layer, the cell may be observed to move along. 



In vegetable cells the protoplasmic movement can be well seen in the hairs 

 of the stinging-nettle and Tradescantia and in the cells of Vallisneria and 

 Chara; it is marked by the movement of the granules nearly always embedded 

 in it. For example, if part of a hair of Tradescantia, figure 5, be viewed 

 under a high magnifying power, streams of protoplasm containing crowds of 



FIG. 4. Changes of Form of a White Corpuscle, Sketched at Brief Intervals, 

 show also the ingestion of two small granules. (Schafer.) 



The figures 



granules hurrying along, like the foot-passengers in a busy street, are seen flow- 

 ing steadily in definite directions, some coursing round the film which lines 

 the interior of the cell-wall, and others flowing toward or away from the irregu- 

 lar mass in the center of the cell-cavity. Many of these streams of protoplasm 

 run together into larger ones and are lost in the central mass, and thus ceaseless 

 variations of form are produced. The movement of the protoplasmic granule? 

 to or from the periphery is sometimes called vegetable circulation, whereas the 

 movement of the protoplasm round the interior of the cell is called rotation. 



The first account of the movement of protoplasm was given by Rosel in 

 I 755> as occurring in a small Proteus, probably a large fresh-water ameba. 

 His description was followed twenty years later by Corti's demonstration of 

 the rotation of the cell sap in characeae, and in the earlier part of the century 



