1893. ARTITFUIGIAL. PROGOPLAS IM. 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 amceba. After a time the streaming 
from one centre ceases, a new set of currents form from a new centre, 





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uhas 
or 
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7, e) 
Fic. 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 amceba. 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 
D 
