1893. 



ARTIFICIAL PROTOPLASM. 



33 



These drops show very remarkable streaming movements. While 

 they are in a weak solution of carbonate of potash they remain at 

 rest. But this solution may be removed by drawing pure water under 

 the coverslip on its wax feet by means of pieces of filter paper. 

 Thereupon the drops, if they are not pressed on by the coverslip, 

 move about actively. During this movement they may change in 

 shape, the change consisting in the extrusion of processes of the 

 foam in the direction of the movement. The internal streaming 

 movements can be seen when the opaque drops are cleared by 

 glycerine. It consists of an axial stream from the centre of the drop 

 to the edge in the direction of the movement through the liquid of 

 the whole foam. At the edge the stream turns back over the surface 

 of the drop, and the backward streams so formed join the axial 

 stream posteriorly. All this corresponds very closely with the 

 streams and motion of a simple amoeba. After a time the streaming 

 from one centre ceases, a new set of currents form from a new centre. 



Fig. 2. — Figures of streaming movements observed in a drop. 



and movement in a different direction occurs. Sometimes several 

 centres of streaming are present together, and the whole drop 

 excessively resembles an amoeba. The streaming goes on from 24 

 hours to at most six days (Fig. 2). 



The theoretical explanation of these movements depends on sur- 

 face tensions. When a liquid is brought towards a drop of a second 

 liquid suspended in a third, if the surface tension is less between 

 the first and second than between the second and third, as the 

 first liquid approaches the second the drop of the second stretches out 

 towards the first, and a set of streaming movements occurs. Thus, 

 in the figure some soap solution (first liquid) is brought up towards 

 a drop of oil (second liquid) suspended in water (third liquid). Then 

 the drop of oil moves gradually into the soap solution, and the 

 currents shown by arrows in the figure appear (Fig. 3). The surface 

 tension between the oil and soap solution is less than the 

 surface tension between the oil and water. The equilibrium is 

 destroyed and the soap solution spreads round on the drop from the 



