278 LOCOMOTORY AND PROTOPLASMIC MOVEMENTS 



solution do in fact resemble the amoeboid movements of certain 

 organisms l . 



Locomotion is possible in a definite direction without any pronounced 

 amoeboid changes of shape, as for instance when a drop of olive-oil, or 

 of paraffin-oil, lying in water is in contact with a soap-solution on one 

 side. The local diminution of surface-tension produced on this side causes 

 the drop to bulge towards the soap-solution, while the peripheral layer of oil 

 is drawn by the surface-tension film from the region of low to that of high 

 tension. In this way a definite circulation is maintained in the oil-drop, and 

 also in the neighbouring soap-solution, for as the film is drawn over the 

 drop the adhering soap-solution is diluted and the surface-tension raised 2 . 

 At the same time the drop of oil progresses towards the soap-solution, 

 that is to the side of least surface-tension 3 . In the same way drops of 

 castor-oil floating in dilute alcohol move towards chloroform, or potassium 

 hydrate 4 , and according to Bernstein 5 drops of mercury move towards 

 potassium bicromate. 



Similar effects are shown when a drop of a mixture of olive-oil and 

 potassium carbonate is placed in pure water, the lowering of surface-tension 

 being in this case produced by the soap, which rises to the surface of the 

 drop and spreads over its exterior 6 . The protoplast can, therefore, always 

 create the physical conditions for a change of shape or for streaming by 

 appropriate metabolic activity. In the same way by the activity of the 

 nucleus, of the chloroplastids, or of the surrounding protoplasm, internal 

 changes of surface-tension may be produced capable of causing changes of 

 shape or internal streaming. The cytoplasm of streaming cells does 

 in fact appear to behave like an emulsion in which the surface-tension 

 changes on the individual drops are responsible for the movement, and in 

 which the whole energy of movement is liberated internally 7 . 



Changes of surface-tension inducing movement may also be produced 

 by electrical means. Thus Ermann observed in 1809 that if the positive 

 terminal of an electrical battery was connected with a drop of mercury 

 lying in dilute sulphuric acid, and the negative terminal was placed in 

 the acid, the mercury moved away from the positive pole. The principle 

 is in fact the same as that of Lippmann's capillary electrometer, and 

 a feeble current will produce relatively considerable movement. 



The amoeboid movements of fluid masses of protoplasm can only be 



1 Cf. Berthold, Protoplasmamechanik, 1886, p. 96. 



2 Butschli, 1. c., p. 43. Additional instances are given by Berthold and Rhumbler. 



3 Butschli, 1. c., p. 44. 



* Rhumbler, Physikalische Zeitschrift, 1899, Nr. 3. 



8 Bernstein, Pfliiger's Archiv f. Physiologic, 1900, Bd. LXXX, p. 628. 



Cf. Butschli, 1. c., p. 33. 



1 Cf. Ewart, Protoplasmic Streaming in Plants, 1903, pp. 113, 116. 



