LIVING SUBSTANCE 



95 



{Fig. 34, a). They can be observed also in the streaming proto- 

 plasmic strands of the uninjured plant-cell, when the electric 

 current is sent through them. The protoplasm then collects at 

 ■once into globules and small spindle-shaped masses, which, if the 

 current be interrupted, become again extended and united, their 

 substance flowing on (Fig. 35). 

 The same can be seen in the 

 pseudopodial filaments of many 

 marine Bhizopoda upon shaking 

 them strongly or continually 

 (Fig. 36), and likewise in many 

 ■other objects. 



A third phenomenon that 

 points to the liquid consistency 

 ■of protoplasm, and one that can 

 be observed in very different 

 forms of cells, is the assumption 

 ■of the glohule- or drop-shape hy 

 uccurmilations of liquid enclosed 

 within the protoplasm, such as 

 the so-called vacuoles, and the 

 fat- and oil-droplets, which ap- 

 pear here and there, increase in 

 size, and under certain circum- 

 stances disappear (Fig. 34, h). 

 Were the ground-mass of pro- 

 toplasm stiff, it would be incom- 

 prehensible that these droplets 

 of liquid of very different sizes 

 always assume the spherical form 

 and preserve it during their 

 growth, as oil-droplets do. In 

 such cases a spherical form is 

 inechanically possible only when 

 the surrounding medium exer- 

 cises upon all sides equal pres- 

 sures and yields equally, i.e., 

 when it is itself a liquid. 



Innumerable phenomena of this kind may be cited, which are 

 compatible only with the liquid nature of protoplasm. But those 

 mentioned suffice completely to show that vital phenomena can 

 very well be associated with a liquid substratum. Of course the 

 liquid and the solid conditions of a body cannot be separated from 

 one another by a sharp limit, but are united by imperceptible 

 transitions. According to our present physical ideas the difference 

 between the gaseous, liquid and solid conditions of a body depends 

 solely upon the fact that in the first the molecules are in rapid 



Fig. 35. — Tradescantia. Cell of a stamen-hair. 

 A, Containing quietly streaming proto- 

 plasm. B, The same cell stimulated by an 

 induced current. The protoplasm in the 

 strands has become rounded into single 

 globules (c, d). (After Kiihne.) 



