628 THE AMERICAN NATURALIST. [Vol. XXXVIII. 



very striking. The movements are caused as follows : The 

 potassium carbonate is dissolved by the water and acts on the 

 oil, forming soap. Thus after a time the oil drop is permeated 

 throughout by minute globules of soapy water, forming a foam- 

 like emulsion. At times one of these globules of soap bursts 

 on the outside of the drop of oil ; the soap then spreads over 

 the surface of the oil, lowering its surface tension in the region 

 affected. At once a projection is formed here, currents flow 

 from within the drop toward the region of lowered tension, and 

 the entire drop may move in that direction. 



Biitschli held that the movements of Amoeba take place in a 

 similar manner. He considers that protoplasm has an emulsion 

 structure similar in a general way to that of the oil drops, — 

 though of course the constituents are not the same. At times 

 the meshwork enclosing the globules breaks at the outer surface 

 of the Amoeba, allowing some of the enclosed fluid to spread 

 over the surface. This lowers the surface tension, causing 

 Amoeba to move in the same manner as the drop of oil. 



Biitschli is inclined to attach much significance to the fact 

 that the oil drops which move in the way described have a foam- 

 like emulsion structure, and to consider this as a support to his 

 view that the similarly moving protoplasm is similarly consti- 

 tuted. But such movements are by no means specially charac- 

 teristic of fluids having a foam-like or emulsion structure ; many 

 drops having this structure do not show the movements, while 

 other drops which have not this structure show the movements 

 equally well, as we shall see. The movements require only that 

 there shall be some method of producing local changes in sur- 

 face tension; this may be easily brought about without the 



Bernstein (:oo) produced similar movements in drops of 

 mercury. Sufficient mercury to make a drop or disk five to ten 

 millimetres in diameter is placed in a flat-bottomed watch-glass. 

 Over it is poured some 20 f nitric acid, and thereto is added a 

 quantity of a strong solution of potassium bichromate. The 

 mixture acts chemically on the mercury, lowering its surface 

 tension. The intensity of the action varies locally, so that the 

 surface tension is decreased now here, now there. As a result 



